Brown D, Hitchcock M J, Katz E
Can J Microbiol. 1986 Jun;32(6):465-72. doi: 10.1139/m86-086.
Two forms of kynurenine formamidase (EC 3.5.1.9; aryl-formylamine amidohydrolase) are present in extracts of Streptomyces parvulus. The higher molecular weight enzyme (Mr = 42 000), kynurenine formamidase I, appears to be constitutive and is present at relatively constant but low levels in antibiotic producing and nonproducing cultures, whereas the synthesis of the lower molecular weight form (Mr = 25 000), kynurenine formamidase II, is initiated just prior to the onset of actinomycin formation. It is postulated (i) that kynurenine formamidase II catalyzes the second step in the pathway from tryptophan----actinocin, and (ii) that it is regulated specifically for the specialized function of actinomycin biosynthesis. The role of kynurenine formamidase I is unknown. Formamidase I and II activities were purified from extracts of S. parvulus and kinetic parameters of the two enzymes were determined. Although some of the properties of the two enzymes are quite similar (substrate specificities, Km values), some striking differences were noted (pH and temperature optima, molecular size, chromatographic properties, sensitivity to certain ions and chemicals). Mutant studies suggest that expression of the gene(s) coding for formamidase II activity play an essential role in regulating the formation of actinocin and, hence, antibiotic synthesis. Kynurenine formamidase activity was also found in a representative number of Streptomyces species and related organisms suggesting that the enzyme may function in the degradative metabolism of tryptophan by certain actinomycetes in nature.
短小链霉菌提取物中存在两种犬尿氨酸甲酰胺酶（EC 3.5.1.9；芳基甲酰胺酰胺水解酶）。分子量较高的酶（Mr = 42 000），即犬尿氨酸甲酰胺酶I，似乎是组成型的，在产生抗生素和不产生抗生素的培养物中均以相对恒定但较低的水平存在，而分子量较低的形式（Mr = 25 000），即犬尿氨酸甲酰胺酶II的合成在放线菌素形成开始之前就已启动。据推测，（i）犬尿氨酸甲酰胺酶II催化从色氨酸到放线菌素途径中的第二步，（ii）它针对放线菌素生物合成的特殊功能进行特异性调节。犬尿氨酸甲酰胺酶I的作用尚不清楚。从短小链霉菌提取物中纯化了甲酰胺酶I和II的活性，并测定了这两种酶的动力学参数。尽管这两种酶的一些性质非常相似（底物特异性, Km值），但也注意到了一些显著差异（最适pH和温度、分子大小、色谱性质、对某些离子和化学物质的敏感性）。突变体研究表明，编码甲酰胺酶II活性的基因表达在调节放线菌素的形成以及抗生素合成中起着至关重要的作用。在许多代表性的链霉菌属物种和相关生物中也发现了犬尿氨酸甲酰胺酶活性，这表明该酶可能在自然界中某些放线菌对色氨酸的降解代谢中发挥作用。
