In this paper, the effect of acidity of zeolites with FER framework was studied in the methanol dehydration to dimethyl ether reaction, by comparing catalysts with different Si/Al ratios(namely 8, 30 and60). The aim o...In this paper, the effect of acidity of zeolites with FER framework was studied in the methanol dehydration to dimethyl ether reaction, by comparing catalysts with different Si/Al ratios(namely 8, 30 and60). The aim of this work was to investigate how the acid sites concentration, strength, distribution and typology(Br?nsted and Lewis) affect methanol conversion, DME selectivity and coke formation. It was found that the aluminium content affects slightly acid sites strength whilst a relevant effect on acid sites concentration and distribution(Br?nsted/Lewis) was observed as 24% of Lewis sites were found on Alrichest samples, whilst less than 10% of Lewis acid sites were observed on FER at higher Si/Al ratio. All the investigated catalyst samples showed a selectivity toward DME always greater than 0.9 and samples with the lowest Si/Al ratio exhibit the best performances in terms of methanol conversion, approaching the theoretical equilibrium value(around 0.85) at temperatures below 200 °C. Turnover-frequency analysis suggests that this result seems to be related not only to the higher amount of acid sites but also that the presence of Lewis acid sites may play a significant role in converting methanol. On the other hand, the presence of Lewis acid sites, combined with a high acidity, promote the formation of by-products(mainly methane) and coke deposition during the reaction. As final evidence, all the investigated catalysts exhibit very high resistance to deactivation by coke deposition, over 60 h continuous test, and a GC–MS analysis of the coke deposited on the catalyst surface reveals tetra-methyl benzene as main component.展开更多
As is known to all, nitrogen not only plays an important role in the industrial development of human society but also plays an important part in the proteins that constitute the essence of life[1]. In 1910, the Haber-...As is known to all, nitrogen not only plays an important role in the industrial development of human society but also plays an important part in the proteins that constitute the essence of life[1]. In 1910, the Haber-Bosch process was first used to synthesize ammonia.展开更多
A transparent gel-like mesoporous silicoaluminophosphate material (SAP) with a Si/Al molar ratio of 20 was synthesized by hydrothermal method. The physicochemical features of SAP were characterized by XRD, XRF, BET, S...A transparent gel-like mesoporous silicoaluminophosphate material (SAP) with a Si/Al molar ratio of 20 was synthesized by hydrothermal method. The physicochemical features of SAP were characterized by XRD, XRF, BET, SEM and FT-IR spectroscopy of pyridine adsorption techniques. The results indicated that incorporation of phosphorus (P) into aluminasilica system altered the basic textural characteristics of aluminasilica. Especially after hydrothermal treatment, the material with large special surface area (up to 492 m 2 /g) exhibited a good performance on hydrothermal stability. Moreover, the phosphorus modifier can not only increase the amount of Bro¨nsted acidic sites (up to 48.44 μmol/g) and the percentage of weak acidic sites in total acidic sites, but also regulate the acid type, such as the ratio of B/L (Bro¨nsted acid/Lewis acid) increases to 1.15. The performances of samples as matrices for the catalytic cracking of heavy vacuum gas oil (VGO) were investigated. At 520 C, the catalysts showed much higher gasoline and diesel oil yields achieving to 45.59 wt% and 19.20 wt%, respectively, and lower coke selectivity (2.86%) than conventional FCC matrices, such as kaolin and amorphous silica-alumina.展开更多
The use of silver metal for hydrodeoxygenation(HDO) applications is scarce and different studies have indicated of its varying HDO activity. Several computational studies have reported of silver having almost zero tur...The use of silver metal for hydrodeoxygenation(HDO) applications is scarce and different studies have indicated of its varying HDO activity. Several computational studies have reported of silver having almost zero turnover frequency for HDO owing to its high C\\O bond breaking energy barrier and low carbon and oxygen binding energies.Herein this work, titania supported silver catalysts were synthesized and firstly used to examine its phenol HDO activity via experimental reaction runs. BET, XRD, FESEM, TEM, EDX, ICP–OES, Pyridine-FTIR, NH_3-TPD and H_2-TPD analyses were done to investigate its physicochemical properties. Phenomena of hydrogen spillover and metal–acid site synergy were examined in this study. With the aid of TiO_2 reducible support, hydrogen spillover and metal–acid site interactions were observed to a certain extent but were not as superior as other Pt, Pd, Ni-based catalysts used in other HDO studies. The experimental findings showed that Ag/TiO_2 catalyst has mediocre phenol conversion but high benzene selectivity which confirms the explanation from other computational studies.展开更多
Nickel and sulfate co-modified CeO2-ZrO2 catalysts were prepared by sol-gel method. The catalysts were characterized by XRD, FTIR, XPS, NH3 chemisorption and NH3-SCR activity tests. The results showed that the enhance...Nickel and sulfate co-modified CeO2-ZrO2 catalysts were prepared by sol-gel method. The catalysts were characterized by XRD, FTIR, XPS, NH3 chemisorption and NH3-SCR activity tests. The results showed that the enhanced acidity of CeO2-ZrO2 catalysts by nickel and sulfate co-modification was responsible for the broadened temperature window and improved the selectivity to N2 in NH3-SCR deNOx. The introduction of nickel to CeO2-ZrO2 solid solutions resulted in more Ce3+ on surface of catalyst, leading to an increased Lewis acidity of catalyst. Higher Lewis acidity of catalyst facilitated ammonia activation at low temperature (<300 oC) and thereby improved the NH3-SCR activity. The enhanced high-temperature (>300 oC) activity and selectivity of catalysts arose from the introduction of Brnsted acid sites (less oxidative than Lewis acid sites) by sulfate modification.展开更多
A pot experiment was conducted to investigate the effects of various soil treatments on the growth of vetiver grass ( Vetiveria zizanioides (L.) Nash) with the objective of formulating appropriate soil media for use i...A pot experiment was conducted to investigate the effects of various soil treatments on the growth of vetiver grass ( Vetiveria zizanioides (L.) Nash) with the objective of formulating appropriate soil media for use in sulfide-bearing mined areas. An acidic mine site acid sulfate soil (pH 2.8) was treated with different soil conditioner formula including hydrated lime, red mud (bauxite residues), zeolitic rock powder, biosolids and a compound fertilizer. Soils treated with red mud and hydrated lime corrected soil acidity and reduced or eliminated metal toxicity enabling the establishment of vetiver grass.Although over-liming affected growth, some seedlings of vetiver survived the initial strong alkaline conditions. Addition of appropriate amounts of zeolitic rock powder also enhanced growth, but over-application caused detrimental effects. In this experiment, soil medium with the best growth performance of vetiver was 50 g of red mud, 10 g of lime, 30 g of zeolitic rock powder and 30 g of biosolids with 2000 g of mine soils (100% survival rate with the greatest biomass and number of new shoots), but adding a chemical fertilizer to this media adversely impacted plant growth. In addition, a high application rate of biosolids resulted in poorer growth of vetiver, compared to a moderate application rate.展开更多
Oxides with different crystal phases can have important effects on the configuration of surface atoms,which can further affect the distribution of hydrogenation sites and acidic sites as well as the competitions of th...Oxides with different crystal phases can have important effects on the configuration of surface atoms,which can further affect the distribution of hydrogenation sites and acidic sites as well as the competitions of these varied types of catalytic sites.This could be potentially used to tailor the distribution of the products.In this study,zirconium oxides with different crystal phases supported copper catalysts were prepared for the hydrogenation of the biomass-derived furfural,vanillin,etc.The results showed that both calcination temperature and Cu species affected the shift of zirconia from tetragonal phase to the monoclinic phase.Monoclinic zirconia supported copper catalyst can effectively catalyze the hydrogenation of furfural to furfuryl alcohol via hydrogenation route due to its low amount of Brønsted acidic sites,although the surface area and the exposed metallic Cu surface area were much lower than the tetragonal zirconia supported copper catalyst.Zirconia with tetragonal or tetragonal/monoclinic phases supported copper catalysts contain abundant acidic sites and especially the Br?nsted acidic sites,which catalyzed mainly the conversion of furfural via the acid-catalyzed routes such as the acetalization,rather than the hydrogenation.The acidic sites over the Cu/ZrO_(2)catalyst played more predominant roles than the hydrogenation sites in determining the conversion of the organics like furfural and vanillin.展开更多
The toxicity of benzene is well known, and its leukemia effect has established. It is a natural constituent of crude oil and the diseases related to its exposure are recognized as occupational diseases. <strong>...The toxicity of benzene is well known, and its leukemia effect has established. It is a natural constituent of crude oil and the diseases related to its exposure are recognized as occupational diseases. <strong>Objective:</strong> To assess occupational exposure of benzene to workers in an oil and gas production company. <strong>Materials and Methods:</strong> Firstly, it was a descriptive, cross-sectional study which consisted of benzene atmospheric quantification in a sample individual measurement of a homogeneous exposure group of workers. Secondly, urinary assays of S-phenylmercapturic acid have been performed at the end of the shift in the selected workers.<strong> Results:</strong> The study has included 79 (47.88%) workers, 17 atmospheric samples were usable and 79 urinary assays at the end of the shift were performed. The average benzene concentration for all sites was 10 times lower than the regulatory average exposure value (1 ppm = 3.2 mg/m<sup>3</sup>): average: 0.122 pp, median: 0.053 ppm and range: 0.019 - 1.448 ppm. All 79 urinary assays of S-phenylmercapturic acid with a biological exposure index of less than 25 μg/g creatinine: mean: 0.70 μg/g creatinine, median: 0.52 μg/g creatinine and extends: 0.23 to 6.7 μg/g creatinine. <strong>Conclusion:</strong> Exposure was below to the limit value for benzene in both atmospheric metrology and biometrology. Therefore it is an occupational group with low exposure to benzene. Thus, the medical supervision will be adapted according to the potentially exposing tasks.展开更多
Objective To investigate the junction of Sp1 consensus sites to human telomerase reverse tran-scriptase (hTERT) promoter in different cell lines and in TRA-treated Hela cell. Methods Different length ofhTERT promoter ...Objective To investigate the junction of Sp1 consensus sites to human telomerase reverse tran-scriptase (hTERT) promoter in different cell lines and in TRA-treated Hela cell. Methods Different length ofhTERT promoter was cloned and inserted into pGL3/basic reporter plasmid. The last four Sp1 sites were deleted byPCR and pGL3B/TRTP413Δ reporter plasmid was constructed. All reporter plasmids were transiently transfected in-to 293, A549, Hela and HepG2 cell lines. 48 h after transfection, luciferase activity was analyzed. hTERT promoteractivity of Hela cell which was treated with trans-retinoid acid (TRA) was tested too. Total RNA of these cells wereextracted and reverse transcript. hTERT mRNA level was analyzed in all tested cells. c-Myc and Sp1 expression wereexamined in Hela cell before and after TRA treatment. U937 was used as a positive control in TRA treatment.Results hTERT was expressed at different level in all tested cell lines. 207bp promoter upstream of transcriptionstart site maintained complete activity. Deletion of last 4 Sp1l sites greatly decreased activity of hTERT promoter, andalmost eliminated its activity in HepG2. TRA increased the activity of different length hTERT promoters in Hela cell,but the activity of Sp1 site-deleted promoter decreased by 3 times. Unlike U937 cell, hTERT expression of Hela cellincreased after TRA treatment, and c-Myc and Sp1 mRNA level were relatively stable. Conclusion Sp1 site wasrequired for transactivation of hTERT promoter and played an important role during TRA treatment.展开更多
In this research work,three kinds of activated bentonite used as solid acid catalysts had been synthesized and studied on removal of olefins from the reformate oil.Activated bentonite samples were analyzed using the B...In this research work,three kinds of activated bentonite used as solid acid catalysts had been synthesized and studied on removal of olefins from the reformate oil.Activated bentonite samples were analyzed using the BET and pyridine-FTIR measurements to investigate their physical and chemical properties.The results showed that both textural properties and surface acidity of the bentonite could affect the catalytic activity.Among the catalyst samples,one kind of bentonite purchased from Hubei with high surface area,high pore volume and more acid sites revealed high activity in removing olefins from the reformate.展开更多
The active site motif of proteins belonging to "Histidine Acid Phosphatase" (HAP) contains a hepta-peptide region, RHGXRXP. A close comparison among fungal and yeast HAPs revealed the fourth residue of the h...The active site motif of proteins belonging to "Histidine Acid Phosphatase" (HAP) contains a hepta-peptide region, RHGXRXP. A close comparison among fungal and yeast HAPs revealed the fourth residue of the hepta-peptide to be E instead of A, which is the case with A. niger PhyA phytase. However, another phytase, PhyB, from the same microorganism has a higher turnover number and it shows E in this position. We mutated A69 residue to E in the fungal PhyA phytase. The mutant phytase shows a myriad of new kinetic properties. The pH profile shifted 0.5 pH unit in both 5.0 and 2.5 bi-hump peaks. The optimum temperature shifted down from 58℃ to 55℃. However, the greatest difference was observed in the mutant protein's reaction to GuCl at a concentration of 0.1 to 0.2 M. The activity of the mutant phytase jumped 100% while the wild type protein showed no activity enhancement in the same concentration range of GuCl. The kinetics performed at higher concentration of GuCl also contrasted the difference between the wild type and mutant phytase. While Km was least affected, the Vmax increased for the mutant and decreased for the wild type. The sensitivity towards myo-inositol hexasulfate, a potent inhibitor, was decreased by the mutation. All in all, A69E mutation has affected a multitude of enzymatic properties of the protein even though the residue was thought to be non-critical for phytase's catalytic function notwithstanding its location in the conserved hepta-peptide region of the biocatalyst.展开更多
文摘In this paper, the effect of acidity of zeolites with FER framework was studied in the methanol dehydration to dimethyl ether reaction, by comparing catalysts with different Si/Al ratios(namely 8, 30 and60). The aim of this work was to investigate how the acid sites concentration, strength, distribution and typology(Br?nsted and Lewis) affect methanol conversion, DME selectivity and coke formation. It was found that the aluminium content affects slightly acid sites strength whilst a relevant effect on acid sites concentration and distribution(Br?nsted/Lewis) was observed as 24% of Lewis sites were found on Alrichest samples, whilst less than 10% of Lewis acid sites were observed on FER at higher Si/Al ratio. All the investigated catalyst samples showed a selectivity toward DME always greater than 0.9 and samples with the lowest Si/Al ratio exhibit the best performances in terms of methanol conversion, approaching the theoretical equilibrium value(around 0.85) at temperatures below 200 °C. Turnover-frequency analysis suggests that this result seems to be related not only to the higher amount of acid sites but also that the presence of Lewis acid sites may play a significant role in converting methanol. On the other hand, the presence of Lewis acid sites, combined with a high acidity, promote the formation of by-products(mainly methane) and coke deposition during the reaction. As final evidence, all the investigated catalysts exhibit very high resistance to deactivation by coke deposition, over 60 h continuous test, and a GC–MS analysis of the coke deposited on the catalyst surface reveals tetra-methyl benzene as main component.
基金supported by the National Key R&D Program of China(2017YFA0208300 and 2017YFA0700104)the National Natural Science Foundation of China(21671180 and 21406184)+2 种基金the Chengdu International Science and Technology Cooperation Fund(2020GH0200069HZ)the funding support from CAS Fujian Institute of Innovationfinancially supported by the DNL Cooperation Fund(DNL201918)。
文摘As is known to all, nitrogen not only plays an important role in the industrial development of human society but also plays an important part in the proteins that constitute the essence of life[1]. In 1910, the Haber-Bosch process was first used to synthesize ammonia.
基金supported by the National Program on Key Basic Research Project(973Program)(Grant No.2012CB215000)the Fundamental Research Funds for the Central Universities(Grant No.12CX04038A)the Graduate Student Innovation Foundation of China University of Petroleum(Grant No.CX-1211)
文摘A transparent gel-like mesoporous silicoaluminophosphate material (SAP) with a Si/Al molar ratio of 20 was synthesized by hydrothermal method. The physicochemical features of SAP were characterized by XRD, XRF, BET, SEM and FT-IR spectroscopy of pyridine adsorption techniques. The results indicated that incorporation of phosphorus (P) into aluminasilica system altered the basic textural characteristics of aluminasilica. Especially after hydrothermal treatment, the material with large special surface area (up to 492 m 2 /g) exhibited a good performance on hydrothermal stability. Moreover, the phosphorus modifier can not only increase the amount of Bro¨nsted acidic sites (up to 48.44 μmol/g) and the percentage of weak acidic sites in total acidic sites, but also regulate the acid type, such as the ratio of B/L (Bro¨nsted acid/Lewis acid) increases to 1.15. The performances of samples as matrices for the catalytic cracking of heavy vacuum gas oil (VGO) were investigated. At 520 C, the catalysts showed much higher gasoline and diesel oil yields achieving to 45.59 wt% and 19.20 wt%, respectively, and lower coke selectivity (2.86%) than conventional FCC matrices, such as kaolin and amorphous silica-alumina.
基金GSP-MOHE,University of Malaya for fully funding this study through the project number "MO008-2015"Ministry of Higher Education of Malaysia (MOHE) for MyBrain15 (MyPhD) programIPPP for project "PG081-2016A"
文摘The use of silver metal for hydrodeoxygenation(HDO) applications is scarce and different studies have indicated of its varying HDO activity. Several computational studies have reported of silver having almost zero turnover frequency for HDO owing to its high C\\O bond breaking energy barrier and low carbon and oxygen binding energies.Herein this work, titania supported silver catalysts were synthesized and firstly used to examine its phenol HDO activity via experimental reaction runs. BET, XRD, FESEM, TEM, EDX, ICP–OES, Pyridine-FTIR, NH_3-TPD and H_2-TPD analyses were done to investigate its physicochemical properties. Phenomena of hydrogen spillover and metal–acid site synergy were examined in this study. With the aid of TiO_2 reducible support, hydrogen spillover and metal–acid site interactions were observed to a certain extent but were not as superior as other Pt, Pd, Ni-based catalysts used in other HDO studies. The experimental findings showed that Ag/TiO_2 catalyst has mediocre phenol conversion but high benzene selectivity which confirms the explanation from other computational studies.
基金Project supported by the "863 Project" (2009AA06Z304 and 2009AA064801)
文摘Nickel and sulfate co-modified CeO2-ZrO2 catalysts were prepared by sol-gel method. The catalysts were characterized by XRD, FTIR, XPS, NH3 chemisorption and NH3-SCR activity tests. The results showed that the enhanced acidity of CeO2-ZrO2 catalysts by nickel and sulfate co-modification was responsible for the broadened temperature window and improved the selectivity to N2 in NH3-SCR deNOx. The introduction of nickel to CeO2-ZrO2 solid solutions resulted in more Ce3+ on surface of catalyst, leading to an increased Lewis acidity of catalyst. Higher Lewis acidity of catalyst facilitated ammonia activation at low temperature (<300 oC) and thereby improved the NH3-SCR activity. The enhanced high-temperature (>300 oC) activity and selectivity of catalysts arose from the introduction of Brnsted acid sites (less oxidative than Lewis acid sites) by sulfate modification.
基金Project partly supported by a grant from Expressway International Ltd., USA.
文摘A pot experiment was conducted to investigate the effects of various soil treatments on the growth of vetiver grass ( Vetiveria zizanioides (L.) Nash) with the objective of formulating appropriate soil media for use in sulfide-bearing mined areas. An acidic mine site acid sulfate soil (pH 2.8) was treated with different soil conditioner formula including hydrated lime, red mud (bauxite residues), zeolitic rock powder, biosolids and a compound fertilizer. Soils treated with red mud and hydrated lime corrected soil acidity and reduced or eliminated metal toxicity enabling the establishment of vetiver grass.Although over-liming affected growth, some seedlings of vetiver survived the initial strong alkaline conditions. Addition of appropriate amounts of zeolitic rock powder also enhanced growth, but over-application caused detrimental effects. In this experiment, soil medium with the best growth performance of vetiver was 50 g of red mud, 10 g of lime, 30 g of zeolitic rock powder and 30 g of biosolids with 2000 g of mine soils (100% survival rate with the greatest biomass and number of new shoots), but adding a chemical fertilizer to this media adversely impacted plant growth. In addition, a high application rate of biosolids resulted in poorer growth of vetiver, compared to a moderate application rate.
基金supported by the National Natural Science Foundation of China(No.51876080)the Program for Taishan Scholars of Shandong Province Government。
文摘Oxides with different crystal phases can have important effects on the configuration of surface atoms,which can further affect the distribution of hydrogenation sites and acidic sites as well as the competitions of these varied types of catalytic sites.This could be potentially used to tailor the distribution of the products.In this study,zirconium oxides with different crystal phases supported copper catalysts were prepared for the hydrogenation of the biomass-derived furfural,vanillin,etc.The results showed that both calcination temperature and Cu species affected the shift of zirconia from tetragonal phase to the monoclinic phase.Monoclinic zirconia supported copper catalyst can effectively catalyze the hydrogenation of furfural to furfuryl alcohol via hydrogenation route due to its low amount of Brønsted acidic sites,although the surface area and the exposed metallic Cu surface area were much lower than the tetragonal zirconia supported copper catalyst.Zirconia with tetragonal or tetragonal/monoclinic phases supported copper catalysts contain abundant acidic sites and especially the Br?nsted acidic sites,which catalyzed mainly the conversion of furfural via the acid-catalyzed routes such as the acetalization,rather than the hydrogenation.The acidic sites over the Cu/ZrO_(2)catalyst played more predominant roles than the hydrogenation sites in determining the conversion of the organics like furfural and vanillin.
文摘The toxicity of benzene is well known, and its leukemia effect has established. It is a natural constituent of crude oil and the diseases related to its exposure are recognized as occupational diseases. <strong>Objective:</strong> To assess occupational exposure of benzene to workers in an oil and gas production company. <strong>Materials and Methods:</strong> Firstly, it was a descriptive, cross-sectional study which consisted of benzene atmospheric quantification in a sample individual measurement of a homogeneous exposure group of workers. Secondly, urinary assays of S-phenylmercapturic acid have been performed at the end of the shift in the selected workers.<strong> Results:</strong> The study has included 79 (47.88%) workers, 17 atmospheric samples were usable and 79 urinary assays at the end of the shift were performed. The average benzene concentration for all sites was 10 times lower than the regulatory average exposure value (1 ppm = 3.2 mg/m<sup>3</sup>): average: 0.122 pp, median: 0.053 ppm and range: 0.019 - 1.448 ppm. All 79 urinary assays of S-phenylmercapturic acid with a biological exposure index of less than 25 μg/g creatinine: mean: 0.70 μg/g creatinine, median: 0.52 μg/g creatinine and extends: 0.23 to 6.7 μg/g creatinine. <strong>Conclusion:</strong> Exposure was below to the limit value for benzene in both atmospheric metrology and biometrology. Therefore it is an occupational group with low exposure to benzene. Thus, the medical supervision will be adapted according to the potentially exposing tasks.
基金Supported by Shanghai Science and Technology Development Foundation (01JC14025) and the 4th phase financial support of Shanghai EducationCommittee.
文摘Objective To investigate the junction of Sp1 consensus sites to human telomerase reverse tran-scriptase (hTERT) promoter in different cell lines and in TRA-treated Hela cell. Methods Different length ofhTERT promoter was cloned and inserted into pGL3/basic reporter plasmid. The last four Sp1 sites were deleted byPCR and pGL3B/TRTP413Δ reporter plasmid was constructed. All reporter plasmids were transiently transfected in-to 293, A549, Hela and HepG2 cell lines. 48 h after transfection, luciferase activity was analyzed. hTERT promoteractivity of Hela cell which was treated with trans-retinoid acid (TRA) was tested too. Total RNA of these cells wereextracted and reverse transcript. hTERT mRNA level was analyzed in all tested cells. c-Myc and Sp1 expression wereexamined in Hela cell before and after TRA treatment. U937 was used as a positive control in TRA treatment.Results hTERT was expressed at different level in all tested cell lines. 207bp promoter upstream of transcriptionstart site maintained complete activity. Deletion of last 4 Sp1l sites greatly decreased activity of hTERT promoter, andalmost eliminated its activity in HepG2. TRA increased the activity of different length hTERT promoters in Hela cell,but the activity of Sp1 site-deleted promoter decreased by 3 times. Unlike U937 cell, hTERT expression of Hela cellincreased after TRA treatment, and c-Myc and Sp1 mRNA level were relatively stable. Conclusion Sp1 site wasrequired for transactivation of hTERT promoter and played an important role during TRA treatment.
文摘In this research work,three kinds of activated bentonite used as solid acid catalysts had been synthesized and studied on removal of olefins from the reformate oil.Activated bentonite samples were analyzed using the BET and pyridine-FTIR measurements to investigate their physical and chemical properties.The results showed that both textural properties and surface acidity of the bentonite could affect the catalytic activity.Among the catalyst samples,one kind of bentonite purchased from Hubei with high surface area,high pore volume and more acid sites revealed high activity in removing olefins from the reformate.
文摘The active site motif of proteins belonging to "Histidine Acid Phosphatase" (HAP) contains a hepta-peptide region, RHGXRXP. A close comparison among fungal and yeast HAPs revealed the fourth residue of the hepta-peptide to be E instead of A, which is the case with A. niger PhyA phytase. However, another phytase, PhyB, from the same microorganism has a higher turnover number and it shows E in this position. We mutated A69 residue to E in the fungal PhyA phytase. The mutant phytase shows a myriad of new kinetic properties. The pH profile shifted 0.5 pH unit in both 5.0 and 2.5 bi-hump peaks. The optimum temperature shifted down from 58℃ to 55℃. However, the greatest difference was observed in the mutant protein's reaction to GuCl at a concentration of 0.1 to 0.2 M. The activity of the mutant phytase jumped 100% while the wild type protein showed no activity enhancement in the same concentration range of GuCl. The kinetics performed at higher concentration of GuCl also contrasted the difference between the wild type and mutant phytase. While Km was least affected, the Vmax increased for the mutant and decreased for the wild type. The sensitivity towards myo-inositol hexasulfate, a potent inhibitor, was decreased by the mutation. All in all, A69E mutation has affected a multitude of enzymatic properties of the protein even though the residue was thought to be non-critical for phytase's catalytic function notwithstanding its location in the conserved hepta-peptide region of the biocatalyst.
