Friedrich B, Magasanik B
J Bacteriol. 1977 Aug;131(2):446-52. doi: 10.1128/jb.131.2.446-452.1977.
Urease was purified 24-fold from extracts of Klebsiella aerogenes. The enzyme has a molecular weight of 230,000 as determined by gel filtration, is highly substrate specific, and has a Km for urea of 0.7 mM. A mutant strain lacking urease was isolated; it failed to grow with urea as the sole source of nitrogen but did grow on media containing other nitrogen sources such as ammonia, histidine, or arginine. Urease was present at a high level when the cells were starved for nitrogen; its synthesis was repressed when the external ammonia concentration was high. Formation of urease did not require induction by urea and was not subject to catabolite repression. Its synthesis was controlled by glutamine synthetase. Mutants lacking glutamine synthetase failed to produce urease, and mutants forming glutamine synthetase at a high constitutive level also formed urease constitutively. Thus, the formation of urease is regulated like that of other enzymes of K. aerogenes capable of supplying the cell with ammonia or glutamate.
脲酶从产气克雷伯氏菌提取物中纯化了24倍。通过凝胶过滤测定，该酶的分子量为230,000，具有高度的底物特异性，对尿素的米氏常数为0.7 mM。分离出了一株缺乏脲酶的突变菌株；它不能以尿素作为唯一氮源生长，但能在含有其他氮源如氨、组氨酸或精氨酸的培养基上生长。当细胞缺氮时，脲酶水平较高；当外部氨浓度较高时，其合成受到抑制。脲酶的形成不需要尿素诱导，也不受分解代谢物阻遏。其合成由谷氨酰胺合成酶控制。缺乏谷氨酰胺合成酶的突变体不能产生脲酶，而以高组成水平形成谷氨酰胺合成酶的突变体也组成性地形成脲酶。因此，脲酶的形成与产气克雷伯氏菌其他能够为细胞提供氨或谷氨酸的酶的形成受到相同的调节。
