我们已经研究了具有高度序列同源性的新描述的脱氢酶家族的两种酶，大肠杆菌的1,2-丙二醇氧化还原酶和运动发酵单胞菌的醇脱氢酶II。这些酶在厌氧条件下发挥其代谢作用；在氧气的存在下，它们通过金属催化的氧化系统显示出非常相似的失活模式。用焦碳酸二乙酯滴定组氨酸残基显示在氧化的酶中减少了一个组氨酸残基。活性和灭活酶的枯草杆菌蛋白酶肽图谱的比较显示，一种含组氨酸的肽存在差异，其序列是用于丙二醇氧化还原酶的YNTPH277GVAN和用于醇脱氢酶II的YNLPH277GV。这个组氨酸残基位于10个残基远离一个拟议的金属结合位点，H263XXXH267，需要解释一个位点特异性的自由基机制。这里描述的三个组氨酸残基在该家族的所有酶中都是严格保守的。在本报告中，我们提出组氨酸277是金属催化的氧化系统氧化的目标，并且这种修饰导致两种酶的不可逆失活。
We have studied two enzymes of a newly described family of dehydrogenases with high sequence homology, 1,2-propanediol oxidoreductase of Escherichia coli and alcohol dehydrogenase II of Zymomonas mobilis. These enzymes perform their metabolic role under anaerobic conditions; in the presence of oxygen, they show a very similar inactivation pattern by a metal-catalyzed oxidation system. Titration of histidine residues with diethyl pyrocarbonate showed one histidine residue less in the oxidized enzymes. Comparison of subtilisin peptide maps of active and inactivated enzymes showed a difference in one histidine-containing peptide, the sequence of which is YNTPH277GVAN for propanediol oxidoreductase and YNLPH277GV for alcohol dehydrogenase II. This histidine residue lies 10 residues away from a proposed metal-binding site, H263XXXH267, necessary to explain a site-specific free radical mechanism. The three histidine residues here described are strictly conserved in all enzymes of this family. In this report we propose that histidine 277 is a target for oxidation by a metal-catalyzed oxidation system and that this modification leads to the irreversible inactivation of both enzymes.
