title: 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 (Mr = 60000) composed of apparently identical polypeptide chains (Mr = 29000). 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 straighforward and shows no sign of co-operativity. Evidence is presented that homoserine and threonine 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.
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D001665:Binding Sites; D004789:Enzyme Activation / Q000187:drug effects; D004926:Escherichia coli / Q000201:enzymology*; D006714:Homoserine; D007700:Kinetics; D046911:Macromolecular Substances; D008274:Magnesium / Q000494:pharmacology; D008970:Molecular Weight; D010446:Peptide Fragments / Q000032:analysis; D010770:Phosphotransferases / Q000302:isolation & purification / Q000378:metabolism; D011485:Protein Binding; D013056:Spectrophotometry, Ultraviolet; D013912:Threonine / Q000494:pharmacology
chemical_list: D000596:Amino Acids; D046911:Macromolecular Substances; D010446:Peptide Fragments; D013912:Threonine; D006714:Homoserine; D010770:Phosphotransferases; D008274:Magnesium