Purification and properties of two aromatic aminotransferases in Bacillus subtilis.

摘要: Two enzymes which transaminate tyrosine and phenylalanine in Bacillus subtilis were each purified over 200-fold partially characterized. One of the enzymes, termed histidinol phosphate aminotransferase, is also active with imidazole acetyl as amino group recipient. Previous studies have shown that mutants lacking this enzyme require histidine for growth. Mutants other aromatic aminotransferase are prototrophs. Neither on any substrate involved acid synthesis. The two can be distinguished by a number criteria. Gel filtration analysis indicate aminotransferases molecular weights 63,500 33,000, respectively. Histidinol heat-sensitive, whereas relatively heat-stable, particularly presence alpha-ketoglutarate. Both display typical Michaelis-Menten kinetics their rates reaction. similar pH optima employ ping-pong mechanism action. Km values various substrates suggest predominant responsible transamaination reactions synthesis phenylalanine. This has 4-fold higher affinity than does aminotransferase. Competitive inhibition was observed between tyrosine, phenylalanine, significance fact an plays important role discussed.