Schildkraut I, Greer S
J Bacteriol. 1973 Sep;115(3):777-85. doi: 10.1128/jb.115.3.777-785.1973.
An enzyme activity of Bacillus subtilis has been found that catalyzes the dephosphorylation and deamination of phosphohomoserine to alpha-ketobutyrate, resulting in a bypass of threonine in isoleucine biosynthesis. In crude extracts of a strain deficient in the biosynthetic isoleucine-inhibitable threonine dehydratase, phosphohomoserine was converted to alpha-ketobutyrate. Phosphohomoserine conversion to alpha-ketobutyrate was shown not to involve a threonine intermediate. Single mutational events affecting threonine synthetase also affected the phosphohomoserine-deaminating activity, suggesting that the deamination of phosphohomoserine was catalyzed by the threonine synthetase enzyme. It was demonstrated in vivo, in a strain deficient in the biosynthetic threonine dehydratase, that isoleucine was synthesized from homoserine without intermediate formation of threonine.
已发现枯草芽孢杆菌的一种酶活性可催化磷酸高丝氨酸去磷酸化和脱氨基生成α-酮丁酸，从而在异亮氨酸生物合成中绕过苏氨酸。在生物合成异亮氨酸抑制性苏氨酸脱水酶缺陷菌株的粗提取物中，磷酸高丝氨酸被转化为α-酮丁酸。磷酸高丝氨酸向α-酮丁酸的转化不涉及苏氨酸中间体。影响苏氨酸合成酶的单突变事件也影响磷酸高丝氨酸脱氨基活性，这表明磷酸高丝氨酸的脱氨基由苏氨酸合成酶催化。在生物合成苏氨酸脱水酶缺陷的菌株中进行的体内实验表明，异亮氨酸可由高丝氨酸合成，且无苏氨酸中间体的形成。
