花生幼苗内精氨酸脱羧酶的初步研究

CHARACTERIZATION OF ARGININE DECARBOXYLASE FROM PEANUT SEEDLING

花生体内控制多胺生物合成的主要酶是ＡＤＣ主要定位于代谢活跃的分生组织内。部分纯化（１３倍）的酶最适底物是Ｌ－Ａｒｇ，Ｋｍ值和Ｖｍａｘ依次为０．５６ｍｍｏｌ／Ｌ、０．６６μｌＣＯ２／ｍｇｐｒｏｔｅｉｎ．ｍｉｎ。反应最适ｐＨ和温度为８～８．５和４０～４５℃。该酶对热、乙醇、脲稳定性差。０．８ｍｍｏｌ／ＬＰＬＰ（磷酸吡哆醛）可提高酶活性２１％，ＤＴＴ（二硫苏糖醇）、ＭＥ（巯基乙醇）提高酶的稳定性，对氯苯汞甲酸酯抑制酶活７０％。说明ＡＤＣ可能以ＰＬＰ为辅酶，活性中心含有巯基。６－ＢＡ、ＧＡ３可明显提高酶活性。二价金属离子对酶活性影响很小。Ｓｐｄ（亚精胺）、Ｓｐｍ（精胺）和Ｐｕｔ（腐胺）均不同程度地降低酶活性，多胺的生物合成途经中可能存在反馈调节机制。

Arginine decarboxylase(EC4.1.1.19),a enzyme in polyamine biosynthesis,was found to be localized in apical meristem in peanut seedling.The partially purified enzyme(about 13 fold)readily decarboxylated L arginine,its Km and Vmax value was 0.56mmol/L and 0.66μlCO 2/mg protein·min respectively.Stability of enzyme to temperature,ethyl and urea was lower.Addition of 0.8mmol/L PLP to the reaction mixture caused an increase in the activity of the enzyme by about 21%.DTT and ME caused an increase in stability of the enzyme,p chloromercuribenzoate strongly inhibited the specific activity of the enzyme(70% inhibition).It is suggested that PLP acted as a cofactor of the enzyme and the SH group is involved in enzyme activity.The enzyme activity is stimulated by 6 BA and GA 3.The requirement of divalent metal ions is not evident for the enzyme activity.Inhibition by spermidine,spermine and putrescine suggests possible feed back mechanism in the pathway of polyamine biosynthesis.