Théze J, Kleidman L, St Girons I
J Bacteriol. 1974 May;118(2):577-81. doi: 10.1128/jb.118.2.577-581.1974.
We have partially purified homoserine kinase from a genetically derepressed strain of Escherichia coli K-12. The optimum pH of the enzyme-substrate reaction was 7.8 and the K(m) values for l-homoserine and adenosine 5'-triphosphate were both 3 x 10(-4) M. K(+) (or NH(4) (+)) as well as Mg(2+) were required for its activity. The sedimentation coefficient determined by ultracentrifugation in a sucrose density gradient was 5.0 +/- 0.25S. l-Homoserine was an excellent protector against heat inactivation of homoserine kinase. l-Threonine was a competitive inhibitor of homoserine kinase, suggesting that end-product inhibition of this enzyme plays a role in vivo in the overall regulation of threonine biosynthesis. The specific activity of aspartokinase I-homoserine dehydrogenase I and of homoserine kinase showed a strong positive correlation in extracts from strains under widely varying conditions of genetic or physiological derepression; it was concluded that these two enzymes are coordinately regulated in E. coli K-12.
我们从基因去阻遏的大肠杆菌K-12菌株中部分纯化了高丝氨酸激酶。酶-底物反应的最适pH值为7.8，L-高丝氨酸和腺苷5'-三磷酸的米氏常数（K(m)）均为3×10⁻⁴M。其活性需要钾离子（或铵离子）以及镁离子。通过在蔗糖密度梯度中进行超速离心测定的沉降系数为5.0±0.25S。L-高丝氨酸是高丝氨酸激酶热失活的优良保护剂。L-苏氨酸是高丝氨酸激酶的竞争性抑制剂，这表明该酶的终产物抑制在体内苏氨酸生物合成的整体调控中发挥作用。在基因或生理去阻遏条件差异很大的菌株提取物中，天冬氨酸激酶I-高丝氨酸脱氢酶I和高丝氨酸激酶的比活性呈现出很强的正相关性；由此得出结论，在大肠杆菌K-12中这两种酶是协同调控的。
