A model detailing the conditions for the formation of active enzymes from amino acid monomers in the pre-biotic aqueous environment is proposed, making use of only a minimal number of parameters: the intensity of the ...A model detailing the conditions for the formation of active enzymes from amino acid monomers in the pre-biotic aqueous environment is proposed, making use of only a minimal number of parameters: the intensity of the amino acid source and the experimental rate coefficient for polypeptide hydrolysis. In a closed system with fixed total amino acid concentration, the formation of polypeptides of significant length is precluded by hydrolysis. In the presence of an amino acid source, the behavior of the steady state solutions is dependent on the efficiency of the catalytic activity in the environment. In absence of catalysis the formation of long amino acid chains shows a remarkable similarity to the equilibrium problem, i.e. it is equally unlikely that an active protein forms. In the presence of catalysis the concentration of polypeptides of significant length increases dramatically to about the same order of magnitude as the steady state concentration of the monomers. Besides the important notion of the proto-enzyme concentration, the model offers a link between the given environmental conditions (flux of monomers, rates of the peptide bond formation and hydrolysis, size of the amino acid set) and properties of the polypeptide relevant to its catalytic properties, such as its length and conserved number of residues.展开更多
A computational study on the mechanism for the decarboxylation of pyruvic acid to acetaldehyde catalyzed by pyruvate decarboxylase at the B3LYP/6-31G (d, p) level of theory is presented. The model employed is self-con...A computational study on the mechanism for the decarboxylation of pyruvic acid to acetaldehyde catalyzed by pyruvate decarboxylase at the B3LYP/6-31G (d, p) level of theory is presented. The model employed is self-contained and it does not resort to external groups to provide protons to the various structures in the mechanism. The potential energy surface points at the intramolecular proton transfer from the amino group of the pyrimidine ring in the enamine intermediate to the enol exocyclic carbon as the rate-determining step (with a barrier of 20.55 kcal·mol–1). This value is in reasonable agreement with an estimated barrier of 24.76 kcal·mol–1, derived from the experimental rate constant (4.0 10–5 s–1) for the decarboxylation of α-lactylthiamin.展开更多
This study compares the rates for the formation and destruction of amino acids in the liquid cometary core subjected to radiogenic heating by the β+ decay of the cosmogenic nuclide 26Al. The evolution of the temperat...This study compares the rates for the formation and destruction of amino acids in the liquid cometary core subjected to radiogenic heating by the β+ decay of the cosmogenic nuclide 26Al. The evolution of the temperature and mass of the comet were computed along with the dynamics of relatively complex organic species such as amino acids. Given the experimentally determined rate coefficient for the radiolysis of amino acids in water solution, the destruction of amino acids is virtually completed after an absorbed radiation dose of ~1 kGy. The calculations suggest that the liquid water core in comets with an initial radionuclide abundance that is sufficient to crystallize and melt the original amorphous ice is subjected to a dose of 100 - 1500 kGy. Any amino acid concentration formed in water either by radiolysis of simpler compounds or by thermal processes such as the synthesis of Strecker could not survive the irradiation delivered by the decay of 26Al.展开更多
文摘A model detailing the conditions for the formation of active enzymes from amino acid monomers in the pre-biotic aqueous environment is proposed, making use of only a minimal number of parameters: the intensity of the amino acid source and the experimental rate coefficient for polypeptide hydrolysis. In a closed system with fixed total amino acid concentration, the formation of polypeptides of significant length is precluded by hydrolysis. In the presence of an amino acid source, the behavior of the steady state solutions is dependent on the efficiency of the catalytic activity in the environment. In absence of catalysis the formation of long amino acid chains shows a remarkable similarity to the equilibrium problem, i.e. it is equally unlikely that an active protein forms. In the presence of catalysis the concentration of polypeptides of significant length increases dramatically to about the same order of magnitude as the steady state concentration of the monomers. Besides the important notion of the proto-enzyme concentration, the model offers a link between the given environmental conditions (flux of monomers, rates of the peptide bond formation and hydrolysis, size of the amino acid set) and properties of the polypeptide relevant to its catalytic properties, such as its length and conserved number of residues.
文摘A computational study on the mechanism for the decarboxylation of pyruvic acid to acetaldehyde catalyzed by pyruvate decarboxylase at the B3LYP/6-31G (d, p) level of theory is presented. The model employed is self-contained and it does not resort to external groups to provide protons to the various structures in the mechanism. The potential energy surface points at the intramolecular proton transfer from the amino group of the pyrimidine ring in the enamine intermediate to the enol exocyclic carbon as the rate-determining step (with a barrier of 20.55 kcal·mol–1). This value is in reasonable agreement with an estimated barrier of 24.76 kcal·mol–1, derived from the experimental rate constant (4.0 10–5 s–1) for the decarboxylation of α-lactylthiamin.
文摘This study compares the rates for the formation and destruction of amino acids in the liquid cometary core subjected to radiogenic heating by the β+ decay of the cosmogenic nuclide 26Al. The evolution of the temperature and mass of the comet were computed along with the dynamics of relatively complex organic species such as amino acids. Given the experimentally determined rate coefficient for the radiolysis of amino acids in water solution, the destruction of amino acids is virtually completed after an absorbed radiation dose of ~1 kGy. The calculations suggest that the liquid water core in comets with an initial radionuclide abundance that is sufficient to crystallize and melt the original amorphous ice is subjected to a dose of 100 - 1500 kGy. Any amino acid concentration formed in water either by radiolysis of simpler compounds or by thermal processes such as the synthesis of Strecker could not survive the irradiation delivered by the decay of 26Al.
