U. Roos et C. Bormann, PURIFICATION AND CHARACTERIZATION OF L-HISTIDINE AMINOTRANSFERASE FROM NIKKOMYCIN-PRODUCING STREPTOMYCES-TENDAE TU901, Journal of General Microbiology, 139, 1993, pp. 2773-2778
Cell extracts of Streptomyces tendae grown in nikkomycin production me
dia 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 S. tendae. The e
nzyme was determined by gel filtration and SDS-PAGE to be a homodimer
with a subunit molecular mass of approximately 45 kDa. The aminotransf
erase had maximum activity at pH 7.0 and 37-degrees-C. The enzyme was
highly specific for L-histidine; pyruvate, 2-oxobutyrate, 2-oxovalerat
e and 2-oxocaproate were used as keto acceptors to about the same exte
nt. The reaction mechanism was ping-pong. The K(m) values for L-histid
ine and pyruvate, determined from Lineweaver-Burk plots, were 25 mm an
d 10 mm, respectively. Neither cell extracts of non-producing S. tenda
e mutants nor extracts of Streptomyces lividans, a species that does n
ot synthesize nikkomycins, showed transaminating activity with a narro
w substrate specificity for L-histidine as the amino donor. This stron
gly suggests that the formation of HisAT is essential for nikkomycin p
roduction.