Aird B A, Heinrikson R L, Westley J
Department of Biochemistry, University of Chicago, Illinois 60637.
J Biol Chem. 1987 Dec 25;262(36):17327-35.
A sulfurtransferase has been purified to apparent homogeneity from the prokaryote Acinetobacter calcoaceticus lwoffi by conventional protein fractionation techniques. Steady-state kinetic studies of the enzyme revealed that its formal mechanism varies with the acceptor substrate employed. With inorganic thiosulfate as the sulfane sulfur-donor substrate and cyanide anion as the acceptor, the enzyme was shown to catalyze the reaction by a double displacement mechanism like that of mammalian rhodanese (thiosulfate:cyanide sulfurtransferase, EC 2.8.1.1). In contrast, with a thiol as the acceptor substrate at relatively high concentrations, the reaction proceeds by a single displacement mechanism, reminiscent of catalysis by another sulfur-transferase, thiosulfate reductase, glutathione-dependent (EC 2.8.1.3). When dithiothreitol is the acceptor substrate, the enzyme cycles through both the single and double displacement pathways, with the flux through each depending differentially on the concentration of dithiothreitol employed. In view of both the relaxed acceptor substrate specificity and the corresponding variability of formal mechanism, the more general name of sulfane sulfurtransferase is proposed for this bacterial enzyme.
通过传统的蛋白质分级分离技术，已从原核生物醋酸钙不动杆菌鲁氏亚种中纯化出一种硫转移酶，达到了表观均一性。对该酶的稳态动力学研究表明，其形式机制会因所使用的受体底物而异。以无机硫代硫酸盐作为硫烷硫供体底物，氰根阴离子作为受体时，该酶通过类似于哺乳动物硫氰酸酶（硫代硫酸盐：氰化物硫转移酶，EC 2.8.1.1）的双取代机制催化反应。相比之下，当以相对高浓度的硫醇作为受体底物时，反应通过单取代机制进行，这让人联想到另一种硫转移酶——谷胱甘肽依赖性硫代硫酸盐还原酶（EC 2.8.1.3）的催化作用。当二硫苏糖醇作为受体底物时，该酶会通过单取代和双取代途径循环，通过每条途径的通量分别取决于所使用的二硫苏糖醇的浓度。鉴于受体底物特异性的宽泛性以及相应形式机制的变异性，建议将这种细菌酶命名为硫烷硫转移酶这一更为通用的名称。
