Aminotransferases for aromatic amino acids and aspartate in Bacillus subtilis

Abstract

Two proteins (form A and form B2) with aromatic-amino-acid aminotransferase activity were detected in extracts of Bacillus subtilis. A histidinol phosphate aminotransferase (protein B1) with aminotransferase activity for the aromatic amino acids was also present. The aspartate aminotransferase (L-aspartate:2-oxoglutarate aminotransferase, EC 2.6.1.1) (protein C) also displayed similar activity. Each of the four proteins was isolated free from the others by the successive application of DEAE-cellulose column chromatography and flat-bed isoelectric focusing at pH range 4-6. Form B2 is the major form of the aromatic-amino-acid aminotransferase (aromatic-amino-acid:2-oxoglutarate amino-transferase, EC 2.6.1.57) and the Km values of tyrosine and phenylalanine with this form are somewhat lower than with the minor form A. The Km of tyrosine with histidinol phosphate aminotransferase (protein B1) is in the same range, but the Km of phenylalanine with this enzyme is 12-20 times higher than the corresponding values with the two forms of the aromatic-amino-acid amino-transferase. Apparent molecular weights were estimated with Sephadex gel filtration to be approx. 73 000, 64 000, 54 000 and 66 000 for form A, form B2, histidinol phosphate aminotransferase and aspartate aminotransferase, respectively. Form B2 is being reported for the first time in this communication.