Smith R E, MacQuarrie R
Biochim Biophys Acta. 1979 Apr 12;567(2):269-77. doi: 10.1016/0005-2744(79)90112-8.
Glycerol-3-phosphate dehydrogenase (sn-glycerol-3-phosphate:NAD+ 2-oxido-reductase, EC 1.1.1.8) has been shown to be sensitive to inhibition by iodoacetate. The reaction of the enzyme with iodoacetate, which appears to be a simple bimolecular process, is accompanied by a corresponding loss of enzyme activity. In addition to changes in activity, the alkylation reaction was monitored by the incorporation of radioactivity from iodo[2-14C]acetate, by changes in amino acid composition, and by changes in the content of free sulfhydryl groups. It is concluded that there are two cysteine residues in the native dimeric enzyme which are essential for enzymic activity. The rate of inactivation was relatively insensitive to the presence of various compounds with the exception of NADH which markedly inhibited the reaction. Kinetic and binding studies showed that the binding of NADH prevents alkylation and, conversely, alkylation prevents NADH binding. From the pH dependence of the alkylation reaction, the pKa of the essential sulfhydryl groups was calculated to be 8.5 and it is suggested that the binding of coenzyme is independent of the state of ionization of these groups.
甘油 - 3 - 磷酸脱氢酶（sn - 甘油 - 3 - 磷酸：NAD⁺ 2 - 氧化还原酶，EC 1.1.1.8）已被证明对碘乙酸的抑制敏感。该酶与碘乙酸的反应似乎是一个简单的双分子过程，同时伴随着相应的酶活性丧失。除了活性变化外，通过碘[2 -¹⁴C]乙酸的放射性掺入、氨基酸组成的变化以及游离巯基含量的变化来监测烷基化反应。得出的结论是，天然二聚体酶中有两个半胱氨酸残基对酶活性至关重要。除了NADH显著抑制该反应外，失活速率对各种化合物的存在相对不敏感。动力学和结合研究表明，NADH的结合会阻止烷基化，反之，烷基化会阻止NADH结合。根据烷基化反应的pH依赖性，计算出必需巯基的pKa为8.5，并且表明辅酶的结合与这些基团的电离状态无关。
