苹果果实转化酶的种类和特性研究

Study of Invertase in Apple Fruit

研究表明 ,新红星苹果果实中存在 3种形式的转化酶 ,即可溶性酸性转化酶、可溶性中性转化酶和细胞壁结合酸性转化酶。 1)酸性转化酶的最适反应温度为 4 0℃ ,而中性转化酶为 5 0℃。 DTT(二硫苏糖醇 )显著提高可溶性转化酶的活性 ,3种转化酶活性均受到 Ag+ 和 Hg2 + 的显著抑制 ,表明转化酶的活性部位含巯基基团。转化酶活性还受到二价阳离子 Mn2 + 和 Ca2 + 的显著激活。 2 ) Cu2 + ,Mg2 + 和 Zn2 + 也能提高可溶性酸性转化酶和细胞壁酸性转化酶活性 ,但可溶性中性转化酶受到这些金属离子的部分抑制。 3)可溶性转化酶对蔗糖的K m值小于细胞壁转化酶对蔗糖的 Km值 ,而其 Vmax值大于细胞壁转化酶的 Vmax值 ,说明可溶性转化酶比细胞壁酸性转化酶对蔗糖有较大的亲和力和较强的催化速率。本文对转化酶特性与苹果果实发育的关系进行了讨论。

The experiment conducted with 'Starkrimson' apple fruit, showed that there existed all three isoforms of invertase, namely soluble acid invertase, soluble neutral invertase and cell wall bound invertase in developing apple fruit. The optimum temperature for acid invertase activity was 40℃, but that for neutral invertase activity was 50℃. The results also showed that DTT treatment significantly increased the activities of soluble invertases, however, it had no effect on cell wall bound invertase. The activities of soluble acid invertase, soluble neutral invertase and cell wall bound invertase were significantly inhibited by Hg 2+ and Ag +, but enhanced by Mn 2+ and Ca 2+ . Moreover, Cu 2+ , Mg 2+ and Zn 2+ also increased the activities of acid invertases, including soluble acid invertase and cell wall bound acid invertase, while the activity of soluble neutral invertase was partially inhibited by these metal ions. Soluble invertases had lower Km and higher V max compared with cell wall bound acid invertase according to the kinetic study of invertase with sucrose as reaction substrate. The function of the invertases in sugar metabolism was discussed in relation to the fruit development.