摘要
从成熟香蕉果实中部分纯化了焦磷酸:果糖—6—磷酸磷酸转移酶(PFP)。研究了酶的果糖—2,6—二磷酸的活化动力学特性.果糖—2,6—二磷酸通过降低酶的K_m(F6P)值和增进最大反应速度(V_(max))促进酶的果糖—6—磷酸磷酸化活性。底物(F6P)浓度和温度影响果糖—2,6—二磷酸对酶的活化作用。 本工作中还观察了香蕉成熟过程中PFP和依赖ATP的磷酸果糖激酶(PFK)活性的变化,并对PFP在果实成熟中的生理意义和调节特性进行了讨论。
Pyrophosphate: fructose 6-phosphate phos-photransferase (PFP) has been partially purifiedfrom ripening banana fruit. The kinetic proper-ties of the activation of banana PFP by Fru-2,6-P_2have been studied. Fru-2, 6-P_2 activated enzymeactivity of fructose 6-phosphate phosphorylationby decreasing K_m(F6P) and increasing V_(max)with a K_a of 30 nmol/L. The activatipn of PFPby Fru-2, 6-P_2 was affected by substrate concentra-tion (F6P). The K_a of Fru-2, 6-P_2 was decreasedfrom 34 nmol/L to 18 nmol/L with the increase ofFru-6-P concentration from 0.5 mmol/L to 14mmol/L at 25℃. The influence of temperatureat 10℃ to 40℃ on Fru-2, 6-P_2 activation ofPFP showed that the kinetic properties of thesaturation curve of Fru-2, 6-P_2 changed. En-zyme cooperativity became positive with the in-creased temperature (Hill number changed from0.8 to 1.3 at 10℃ to 40℃ ) and the K_a fro Fru-2,6-P_2 was decreased from 46 nmol/L to 22 nmol/L.The dependence of enzyme Fru-2, 6-P_2activation on Fru-6-P concentrations and tempera-ture indicated that the binding of enzyme withactivator Fru-2, 6-P_2 could be well modulated andwas significant for regulating PFP enzyme activityduring banana fruit ripening. Changes in the activities of PFP and ATP-dependent phosphofructokinase (PFK) wereobserved during banana fruit ripening. PFPactivity increased rapidly after 3～5 days of retar-dation and the activity of PFP was about 10--foldhigher than the activity of PFK at the 6th day(dimacteric peak). Treatment of banana fruitwith ethylene reduced the length of the preclimac-teric period of respiration which was associatedwith the activity of PFP and the progress of fruitripening. The function and regulation of PFP in fruitripening are discussed.
关键词
果糖二磷酸
香蕉
磷酸转移酶
fructose 2,6-P_2
pyrophosphate
fructose 6-phosphate phosphotransferase
fruit ripening
ethylene, phosphofructokinase
