Anderson P M, Little R M
Biochemistry. 1986 Apr 8;25(7):1621-6. doi: 10.1021/bi00355a026.
Cyanase is an inducible enzyme in Escherichia coli that catalyzes the hydrolysis of cyanate. Bicarbonate is required for activity, perhaps as a substrate, and the initial product of the reaction is carbamate, which spontaneously breaks down to ammonia and bicarbonate [Anderson, P. M. (1980) Biochemistry 19, 2882]. The purpose of this study was to characterize the kinetic properties of cyanase. Initial velocity studies showed that both cyanate and bicarbonate act as competitive substrate inhibitors. A number of monovalent anions act as inhibitors. Azide and acetate appear to act as competitive inhibitors with respect to cyanate and bicarbonate, respectively. Chloride, bromide, nitrate, nitrite, and formate also inhibit, apparently as the result of binding at either substrate site. Malonate and several other dicarboxylic dianions at very low concentrations display "slow-binding", reversible inhibition which can be prevented by saturating concentrations of either substrate. The results are consistent with a rapid equilibrium random mechanism in which bicarbonate acts as a substrate, bicarbonate and cyanate bind at adjacent anion-binding sites, and both substrates can bind at the other substrate anion binding site to give a dead-end complex.
氰酸酶是大肠杆菌中的一种诱导酶，可催化氰酸盐的水解。该酶的活性需要碳酸氢盐，可能作为底物，反应的初始产物是氨基甲酸酯，其会自发分解为氨和碳酸氢盐[安德森，P.M.（1980年）《生物化学》19卷，第2882页]。本研究的目的是表征氰酸酶的动力学特性。初始速度研究表明，氰酸盐和碳酸氢盐均作为竞争性底物抑制剂起作用。一些单价阴离子可作为抑制剂。叠氮化物和乙酸盐似乎分别作为氰酸盐和碳酸氢盐的竞争性抑制剂。氯离子、溴离子、硝酸根离子、亚硝酸根离子和甲酸根离子也有抑制作用，显然是由于它们在任一底物位点结合的结果。丙二酸和其他几种二羧酸二价阴离子在极低浓度下表现出“缓慢结合”的可逆抑制作用，这种抑制作用可通过任一底物的饱和浓度来防止。这些结果与一种快速平衡随机机制一致，在该机制中，碳酸氢盐作为底物，碳酸氢盐和氰酸盐在相邻的阴离子结合位点结合，并且两种底物都可以在另一个底物阴离子结合位点结合形成一个终止复合物。
