Cell extracts of grown in nikkomycin production media contained an enzyme (HisAT) that transaminated L-histidine as the sole amino substrate with pyruvate as the amino group acceptor. HisAT was purified about 190-fold from the crude extract of The enzyme was determined by gel filtration and SDS-PAGE to be a homodimer with a subunit molecular mass of approximately 45 kDa. The aminotransferase had maximum activity at pH 7.0 and 37 °dGC. The enzyme was highly specific for L-histidine; pyruvate, 2-oxobutyrate, 2-oxovalerate and 2-oxocaproate were used as keto acceptors to about the same extent. The reaction mechanism was ping-pong. The values for L-histidine and pyruvate, determined from Lineweaver-Burk plots, were 25 mM and 10 mM, respectively. Neither cell extracts of non-producing mutants nor extracts of , a species that does not synthesize nikkomycins, showed transaminating activity with a narrow substrate specificity for L-histidine as the amino donor. This strongly suggests that the formation of HisAT is essential for nikkomycin production.


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