Threonine synthetase-catalyzed conversion of phosphohomoserine to alpha-ketobutyrate in Bacillus subtilis.
An enzyme activity of Bacillus subtilis has been found that catalyzes the dephosphorylation and deamination of phosphohomoserine to alpha-ketobutyrate, resulting in a bypass of threonine in isoleucine biosynthesis. In crude extracts of a strain deficient in the biosynthetic isoleucine-inhibitable threonine dehydratase, phosphohomoserine was converted to alpha-ketobutyrate. Phosphohomoserine conversion to alpha-ketobutyrate was shown not to involve a threonine intermediate. Single mutational events affecting threonine synthetase also affected the phosphohomoserine-deaminating activity, suggesting that the deamination of phosphohomoserine was catalyzed by the threonine synthetase enzyme. It was demonstrated in vivo, in a strain deficient in the biosynthetic threonine dehydratase, that isoleucine was synthesized from homoserine without intermediate formation of threonine.
D000619:Aminohydrolases / Q000378:metabolism; D001412:Bacillus subtilis / Q000201:enzymology / Q000378:metabolism*; D002087:Butyrates / Q000096:biosynthesis*; D002247:Carbon Isotopes; D002474:Cell-Free System; D003641:Deamination; D006714:Homoserine / Q000378:metabolism*; D006836:Hydro-Lyases / Q000378:metabolism; D007532:Isoleucine / Q000096:biosynthesis; D007659:Ketones / Q000096:biosynthesis; D009154:Mutation; D010710:Phosphates / Q000378:metabolism; D013912:Threonine / Q000378:metabolism; D014166:Transferases / Q000378:metabolism*; D014316:Tritium
D002087:Butyrates; D002247:Carbon Isotopes; D007659:Ketones; D010710:Phosphates; D007532:Isoleucine; D014316:Tritium; D013912:Threonine; D006714:Homoserine; D014166:Transferases; D000619:Aminohydrolases; D006836:Hydro-Lyases