Ahmed S I, Bollon A P, Rogers S J, Magee P T
Biochimie. 1976;58(1-2):225-32. doi: 10.1016/s0300-9084(76)80374-4.
Threonine deaminase (L-theonine hydro-lyase (deaminating), E.C. 4.2.1.16) has been purified to homogeneity from extracts of Saccharomyces cerevisiae. When purified 1200-fold, the enzyme is homogeneous by the criterion of sodium dodecyl sulfate-polyacrylamide electrophoresis. The reduced and alkylated protein has a molecular weight of approximately 50,000 daltons, one-fourth the value determined previously for the intact enzyme. The purified enzyme exhibits homotropic effects with the substrate; these effects are descresed in the presence of DL-allothreonine, a competitive inhibitor. Half-maximal velocity is achieved at 34 mM L-threonine in the absence of other effectors. L-isoleucine both stimulates at low (0.01-0.05 mM) concentrations and inhibits at high (0.1-1.0 mM) concentrations. Valine activates the enzyme in the absence of isoleucine ; in the presence of isoleucine it reverses inhibition.
苏氨酸脱氨酶（L-苏氨酸水解酶（脱氨基），E.C. 4.2.1.16）已从酿酒酵母提取物中纯化至同质。纯化1200倍后，根据十二烷基硫酸钠-聚丙烯酰胺电泳标准，该酶是同质的。还原并烷基化的蛋白质分子量约为50,000道尔顿，是先前测定的完整酶分子量的四分之一。纯化的酶对底物表现出同促效应；在竞争性抑制剂DL-别苏氨酸存在下，这些效应会降低。在没有其他效应物的情况下，34 mM L-苏氨酸时达到最大速度的一半。L-异亮氨酸在低浓度（0.01 - 0.05 mM）时刺激，在高浓度（0.1 - 1.0 mM）时抑制。缬氨酸在没有异亮氨酸时激活该酶；在有异亮氨酸存在时，它可逆转抑制作用。
