Homoserine Kinase from Escherichia coli K12

Abstract

Homoserine kinase was purified to apparent homogeneity from a derepressed strain of Escherichia coli K12, using standard fractionation techniques. It is a dimer (M_r= 60000) composed of apparently identical polypeptide chains (M_r= 29 000). Its amino acid composition and N-terminal sequence have been determined. l-Threonine is a competitive inhibitor of the substrate l-homoserine; this inhibition is straightforward and shows no sign of co-operativity. Evidence is presented that homoserine and threotine bind to the same site of this non-allosteric enzyme. The binding of homoserine and threonine can also be studied by difference spectroscopy; the latter studies reveal an unexpected effect of magnesium ions, which might be the basis for the unusual high Mg²⁺ requirement for optimal enzyme reaction