Die Enzyme der Biosynthese aromatischer Aminosäuren bei Hansenula henricii : Die Aminotransferasen

Abstract

In the yeast Hansenula henricii CCY 38-10-2 the tryptophan aminotransferase (EC 2.6.1.27), the tyrosine aminotransferase (EC 2.6.1.5.), the phenylalanine aminotransferase, and the prephenate aminotransferase, an enzyme of the pretyrosine pathway were studied. Pyridoxal-5-phosphate was used as coenzyme by the four aminotransferases. 2-oxo-glutarate was the amino group acceptor for the first three enzymes, while L-glutamate was found to be the best amino group donator for prephenate aminotransferase. The results of the regulation on enzyme level and of the regulation of enzyme synthesis are discussed. It is concluded, that the tyrosine and phenylalanine aminotransferase reaction is catalyzed by the same enzyme, while tryptophan aminotransferase and prephenate aminotransferase are specific enzymes.