小麦旗叶老化期间的内肽酶

Endopeptidases in Wheat Flag Leaves During Aging

小麦叶片中存在着内肽酶，其最适pH为4．8，最适反应温度为45℃。小麦旗叶全展以后，净光合速率和总可溶性蛋白质含量下降，而内肽酶比活上升。用蛋白质合成抑制剂处理的结果表明，有内肽酶的从头合成；用激活制和抑制剂处理的结果表明，小麦叶片中至少有3种类型的内肽酶（即巯基蛋白酶、丝氨酸蛋白酶和金属蛋白酶），而在蛋白质降解中起主要作用的是巯基蛋白酶。另外，氨基酸对内肽酶有保护作用，激素对内肽酶具有调节作用，活性氧对内肽酶的活力上升也有促进作用。

Studies with an activator(DTT) and inhibitors (PMSF, IA andEDTA)have shown that there are at leastthree kinds of endopeptidries in wheatflag leaves, i. e , thiol-proteinases, serineproteinases and metallo-proteinases(Table 1 ). The changes in endopeptidases activity during leaf aging could be divided into two phases. During the firstphase, the activity of endopeptidaseschanged at a low level, but it increasedrapidly in the second phase. This trendcorresponded to the decline in rate of netphotosynthesis and the total soluble protein content (Fig. 1 ). The pH optimumand temperature optimum of Wheat leafendopeptidases and 4. 8 and 45℃, respeptively (Figs. 6, 7 ). Exogenous BAand actidione could prevent the rise ofactivity of endopeptidases, while cysteine, serine and ABA could enhance it(Figs. 3, 4 ). In addition, exogenousH2O2 played a role in enhancing the riseof endopeptidases activity(Fig. 5).