摘要
糖型叶水稻、小麦、苜蓿叶片中SS的活力≥SPS。中间型叶高粱、菠菜叶片和淀粉型叶烟草、大豆叶片中SS的活力<SPS。糖型叶蚕豆叶片中SS的活力亦小于SPS,但SS活力是可观的. 水稻叶片SS催化的反应是可逆的,蔗糖合成反应的最适pH 8.0～9,5,蔗糖裂解反应的最适 pH6.5。蔗糖合成反应的速率随Mg^(2+)浓度增大而加强,逆反应的速率与Mg^(2+)浓度呈负相关。PPi与ATP对蔗糖合成反应无明显影响,对逆反应起抑制作用;UTP对正—逆反应都有抑制作用。ADP,GDP,CDP可取代UDP作为逆反应的底物之一,但效率较差。
The activities of sucrose synthetase andsucrose phosphate synthetase can be detectedin leaves. The activity of sucrose synthetase ishigher than or approximately equals to that ofsucrose phosphate synthetase in plants withsugar leaves, such as rice, wheat, and alfalfa.But in plants with starch leaves and with inter-mediate type of 1eaves, such as soybean, tobacco,spinach and sorghum, the activity of sucroseSynthetase is lower than that of sucrose phos-phate synthetase (Fig. 1). The reaction catalyzed by sucrose synthe-tase in rice leaves is reversible (Table 1). Thesucrose synthesis (forward) reaction catalyzedby this enzyme has a broad pH optimum bet-wee n 8.0～9.5 and the sucrose cleavage (back-ward) reaction has a sharp optimum at pH 6.5(Fig. 2). The rate of forward reaction increasedwhile the rate of backward rcaction decreasedwith the increase of the concentration of Mg^(2+)(Fig. 3). PP_i and ATP had no effect on the forwardreaction but inhibited the backward reaction(Fig.4) The reaction rate of sucrose cleavagedecreased when the PP_i concentration increased.The reactions in both directions were inhibitedby ADP and UTP. Sucrose synthetase can acceptADP, GDP and CDP instead of UDP as asubstrate for the backward reaction, but the rateof fructose formation is lower than UDP. Thesucrose synthesis and cleavage reactions cataly-zed by rice leaf sucrose synthetase are regulatedby pH, Mg^(2+), PPi and nucleotides.
关键词
水稻
蔗糖合成酶
核苷酸
叶片
leaves
sucrose synthetase
sucrose phosphate synthetase
pH
Mg^(2+)
PPi
nucleotides
