Drury E J, MacKenzie R E
Can J Biochem. 1977 Sep;55(9):919-23. doi: 10.1139/o77-137.
Reaction of the bifunctional enzyme formiminoglutamate:tetrahydrofolate formiminotransferase (EC 2.1.2.5) - formiminotetrahydrofolate cyclodeaminase (EC 4.3.1.4) with the sulfhydryl reagent 5,5'-dithiobis (2-nitrobenzoic acid) selectively inactivates the cyclodeaminase. Loss of activity correlates with the modification of two sulfhydryl groups per subunit. The inhibitor folic acid reduces the rates of inactivation and sulfhydryl modification, and protection experiments demonstrate that only one of the two sulfhydryls modified is important for enzyme activity. The results indicate the presence of a cyclodeaminase site on each polypeptide, assuming one sulfhydryl per site, in agreement with a quaternary structure containing identical polypeptides. Modification does not cause dissociation of the enzyme and is reversible with dithiothreitol.
四氢叶酸亚胺甲基转移酶（EC 2.1.2.5）-亚胺甲基四氢叶酸环化脱氨酶（EC 4.3.1.4）与巯基试剂5,5'-二硫代双（2-硝基苯甲酸）反应会选择性地使环化脱氨酶失活。活性丧失与每个亚基两个巯基的修饰相关。抑制剂叶酸降低了失活速率和巯基修饰速率，保护实验表明，两个被修饰的巯基中只有一个对酶活性很重要。结果表明，假设每个位点有一个巯基，则每个多肽上存在一个环化脱氨酶位点，这与含有相同多肽的四级结构一致。修饰不会导致酶的解离，并且用二硫苏糖醇可使其逆转。
