Distinct kynureninase and hydroxykynureninase enzymes in an actinomycin-producing strain of Streptomyces parvulus

Abstract

Extracts of Streptomyces parvulus ATCC 12434 contain enzyme activity which converts kynurenine and hydroxykynurenine to anthranilate and hydroxyanthranilate, respectively. The ratio of activity towards each substrate is variable depending on the age of the culture; kynurenine is preferentially hydrolysed by extracts from younger (zero h) mycelium whereas hydroxykynurenine is more readily hydrolysed by extracts from older (48 h) mycelium. Sephadex G-200 chromatography of a mixture of partially purified extracts from mycelium of both ages revealed a peak of activity toward kynurenine with a molecular weight of 82 000 and a peak of activity toward hydroxykynureninase possessing a molecular weight of 56 000. Thus, it is concluded that distinct kynureninase ( l-kynurenine hydrolase, EC 3.7.1.3) and hydroxykynurenine enzymes are produced by this organism. Both enzymes are induced by the presence of tryptophan in the growth medium. However, just prior to the onset of actinomycin synthesis (in the absence of added tryptophan) only hydroxykynureninase activity increases significantly (50–60-fold) and high levels are subsequently maintained throughout the antibiotic production period. Growth in the presence of glucose or glycerol represses both antibiotic synthesis and the increase in hydroxykynureninase activity. A mutant unable to synthesize actinomycin D displays only a small and transient increase in this activity. It is concluded that hydroxykynureninase is a functional component of the actinomycin biosynthetic system.