光对黄化玉米叶片PEP羧化酶活性和特性的调节

Regulation of Light on the Activity and Properties of PEP Carboxylase in Etiolated Maize Leaves

以玉米为材料，研究了光对其ＰＥＰ羧化酶活性和特定的调节．发现绿苗远比黄化苗中ＰＥＰ羧化酶活性高，光处理后黄化苗中ＰＥＰ羧化酶活性明显增高，这种增高能被环已酰亚胺所抑制，表明是酶蛋白合成致使酶活性增高的过程。绿苗和黄化苗ＰＥＰ羧化酶在Ｋｍ（ＰＥＰ）、Ｋｍ（Ｇ－６－Ｐ）、Ｖｍａｘ和Ｈｉｌｌ系数等动力学常数上存在差异；前者Ｋｍ（ＰＥＰ）、Ｋｍ（Ｇ－６－Ｐ）和Ｖｍａｘ比后者对应的三个动力学常数大，但Ｈｉｌｌ系数比后者小，说明绿苗和黄化营中的ＰＥＰ羧化酶不完全为同一种酶，而是互为同工酶．黄化苗经照光处理后，其ＰＥＰ羧化酶的动力学常数与绿苗．ＰＥＰ羧化酶的动力学常数趋于相同．这进一步证实光诱导黄化苗中合成了ＰＥＰ羧化酶。

The activity of PEPCase in etiolated leaves was much lower than that in green leaves,but could be increased significantly upon light illumination (Tab.1). Inhibition experiment with cycloheximide(Fig. 2) showed that the increases in PEPCase activity and protein content in etiolated leaves was not the result of PEPCase activation,but the result of synthesis of PEPCase induced by light. It was found that Km (PEP),Km (G6P), Vmax and Hill coefficient of PEPCase in green leaves was different from those of etiolated leaves (Tab. 2). The Km (PEP),Km (G6P)and Vmax were higher in green leaves,but the Hill coefficient was lower. When etiolated leaves was illuminated with light (3000 1x) for 3 hours, the Km (PEP), Km(G6P)and Hill coefficient of enzyme became similar to those fin green leaves (Tab. 2).PEPCase in green leaves was more sensitive to G6P(Fig. 1). When etiolated leaves was illuminated with light (3000 1x) for 3 hours, the sensitivity of PEPCase to G6Ptended to be similar to that in green leaves (Fig. 1).The above data from the kinetic constants and the sensitivity to G6P suggested that the formation of a new form of PEPCase was induceed by light.