Arraj J A, Campbell J H
J Bacteriol. 1975 Nov;124(2):849-56. doi: 10.1128/jb.124.2.849-856.1975.
The ebg beta-galactosidase of Escherichia coli K-12 strain LC110 has been purified and characterized. Strain LC110 is a Lac+ revertant of a mutant with a deletion of the lacZ beta-galactosidase gene. Its new ebg beta-galactosidase activity was shown to be due to a discrete protein, immunologically unrelated to lacZ beta-galactosidase. Its kinetics of action conformed to those of a simple conventional enzyme. With o-nitrophenyl-beta-D-galactoside as substrate, the Vmax was 11,200 nmol/min per mg of enzyme, the Km was 5 mM, and the activation energy was 12,400 cal/mol. Corresponding values for lacZ beta-galactosidase of wild-type E. coli K-12 were 350,000 nmol/min per mg of enzyme, 1.3 mM, and 8,000 cal/mol. A series of sugars has been examined as competitive inhibitors of ebg beta-galactosidase. Kinetic analyses suggest that ebg beta-galactosidase has a particularly high affinity for galactosamine and gamma-galactonolactone, binds galatose more tightly than lactose, and shows a general preference for monosaccharides rather than beta-galactosides. We conclude that the ebg beta-galactosidase may have arisen by modification of a gene involved with the metabolism of a monosaccharide, possibly a 2-amino sugar.
大肠杆菌K-12菌株LC110的ebgβ-半乳糖苷酶已被纯化并进行了特性分析。菌株LC110是lacZβ-半乳糖苷酶基因缺失突变体的Lac+回复突变体。其新的ebgβ-半乳糖苷酶活性被证明是由一种离散蛋白引起的，该蛋白与lacZβ-半乳糖苷酶在免疫学上无关。其作用动力学符合简单常规酶的动力学。以邻硝基苯基-β-D-半乳糖苷为底物时，Vmax为每毫克酶11200 nmol/分钟，Km为5 mM，活化能为12400 cal/mol。野生型大肠杆菌K-12的lacZβ-半乳糖苷酶的相应值分别为每毫克酶350000 nmol/分钟、1.3 mM和8000 cal/mol。已检测了一系列糖类作为ebgβ-半乳糖苷酶的竞争性抑制剂。动力学分析表明，ebgβ-半乳糖苷酶对氨基半乳糖和γ-半乳糖内酯具有特别高的亲和力，与半乳糖的结合比乳糖更紧密，并且总体上更倾向于单糖而非β-半乳糖苷。我们得出结论，ebgβ-半乳糖苷酶可能是由参与单糖（可能是2-氨基糖）代谢的基因修饰产生的。
