Homoserine kinase from the phototrophic bacteriumRhodospirillum rubrumis not sensitive to feedback inhibition by l-threonine

Abstract

Abstract Homoserine kinase (EC 2.7.1.39), one of the enzymes of L -threonine synthesis, was purified 200-fold from the phototrophic bacterium Rhodospirillum rubrum strain S1 by salt precipitation, hydrophobic interaction chromatography and gel filtration. The enzyme had a Mr of about 145000 and was active with L -homoserine (Km = 3 mM) and ATP (Km = 0.44 mM). In contrast to the kinase from the enteric bacterium, Escherichia coli, the R. rubrum enzyme was neither stabilized nor inhibited by L -threonine. Of 18 amino acids and metabolites tested (including L -allo-threonine, D -allo-threonine, DL -homocysteine, o-phosphoserine and L -norleucine), none was found to be inhibitory.