Molecular adaptation to photo-oxidative stresses in plants.

抗坏血酸过氧化物酶在茶叶中发现了两种抗坏血酸过氧化物酶同工酶。其中一种被纯化为均质。通过与抗坏血酸过氧化物酶同工酶和愈创木酚过氧化物酶的比较，对该同工酶的酶学和分子特性进行了表征。抗坏血酸过氧化物酶与愈创木酚过氧化物酶在电子供体特异性方面存在差异；对抗坏血酸去除的敏感性；对硫醇类试剂的敏感性；氨基酸末端区域的氨基酸组成和氨基酸序列。抗坏血酸过氧化物酶和过氧化氢与对氨基酚、对甲酚、羟基脲或羟胺孵育可使酶失活。抗坏血酸过氧化物酶产生对氨基酚和羟基脲自由基。这些信号在加入抗坏血酸后消失，发现单脱氢抗坏血酸的信号特征。因此，抗坏血酸过氧化物酶被过氧化物酶反应产生的对氨基酚、对甲酚、羟基脲和羟胺自由基灭活，并通过清除自由基保护抗坏血酸过氧化物酶不被灭活。因此，这些化合物是抗坏血酸过氧化物酶的自杀抑制剂。水稻叶片和种子胚中含有4种cuzn -超氧化物歧化酶（SOD）同工酶和2种Mn-SOD同工酶。CuZn-SOD I是叶片中的主要酶，而不是胚胎和黄化幼苗中的主要酶。CuZn-SODs II、III和IV主要存在于胚中，但在叶片中也存在少量同工酶。从水稻叶片中纯化CuZn-SOD I、II和IV达到均匀性。CuZn-SOD IV为单体酶，其余均为二聚体酶。主要在叶片中表达的CuZn-SOD I与其他主要在非光合组织中表达的CuZn-SOD具有免疫学上的区别。

1). Ascorbate peroxidase Two isozymes of ascorbate peroxidase were found in tea leaves. One of them was purified to homogeneity. The enzymatic and molecular properties of this isozyme were characterized in comparison with the other isozyme of ascorbate peroxidase and with guaiacol peroxidases. Ascorbate peroxidases showed differences from guaiacol peroxidase with respect to the specificity of the electron donor; sensitivity to ascorbate removal; sensitivity to thiol reagents; and amino acid composition and amino acid sequence of the amino terminal region. Incubation of ascorbate peroxidase and hydrogen peroxide with p-aminophenol, p-cresol, hydroxyurea, or hydroxyamine results in the inactivation of the enzyme. The radicals of p-aminophenol and hydroxyurea were produced by ascorbate peroxidase as detected by their ESR signals. These signals disappeared upon addition of ascorbate, and the signal characteristic of monodehydroascorbate was found. Thus, ascorbate peroxidase was inactivated by the radicals of p-aminophenol, p-cresol, hydroxyurea and hydroxyamine which are produced by the perocidase reaction, and it is protected from inactivation by ascorbate via the scavenging of the radicals. Thus, these compounds are suicide inhibitors for ascorbatre peroxidase.2). Superoxide dismutase Rice leaves and seed embryo contain four isozymes of CuZn-superoxide dismutase (SOD) and two isozymes of Mn-SOD. CuZn-SOD I is a major enzyme in leaves, but not in embryos or etiolated seedlings. CuZn-SODs II, III and IV were found in the embryos but were also found as minor isozymes in leaves. CuZn-SOD I, II and IV were purified to homogeneity from rice leaves. CuZn-SOD IV was found to be a monomer and the others were dimeric enzymes. CuZn-SOD I which is expressed mainly in leaves is immunologically distinct from the other CuZn-SODs which are mainly expressed in non-photosynthetic tissues.