Anderson P M, Sung Y C, Fuchs J A
Department of Biochemistry, University of Minnesota-Duluth 55812.
FEMS Microbiol Rev. 1990 Dec;7(3-4):247-52. doi: 10.1111/j.1574-6968.1990.tb04920.x.
Cyanase is an inducible enzyme in E. coli that catalyzes bicarbonate-dependent decomposition of cyanate. It is encoded as part of an operon we have named the cyn operon, which includes three genes in the following order: cynT (cyanate permease), cynS (cyanase), and cynX (protein of unknown function). The direction of transcription is opposite to that of the lac operon, and the 3'-end of the cyn operon overlaps the 3'-end of the lac operon by 98 nucleotides. The gene cynR (regulatory protein) is located upstream from the cyn operon, and its transcription is opposite that of the cyn operon. The genes of the cyn operon and the cynR gene have been cloned, sequenced and over-expressed. Cyanate at concentrations of about 1 mM is toxic to strains of E. coli lacking the cyanase gene, but strains in which the inducible gene for cyanase is present can grow on cyanate as the sole source of nitrogen at concentrations as high as 20 mM. The presence of cyanase itself is not sufficient to overcome cyanate toxicity--the permease must also be present. Strains lacking the cyanase gene, but having a functional permease gene, are extremely sensitive to cyanate. Uptake of cyanate involves the product of the permease gene in an energy-dependent process. It appears that the cyn operon has evolved to function in detoxification/decomposition of cyanate arising from both intra- and extracellular sources.
氰酸酶是大肠杆菌中的一种诱导型酶，可催化依赖于碳酸氢盐的氰酸盐分解。它作为我们命名为cyn操纵子的操纵子的一部分进行编码，该操纵子按以下顺序包含三个基因：cynT（氰酸盐通透酶）、cynS（氰酸酶）和cynX（功能未知的蛋白质）。转录方向与lac操纵子相反，并且cyn操纵子的3'端与lac操纵子的3'端重叠98个核苷酸。基因cynR（调节蛋白）位于cyn操纵子的上游，其转录方向与cyn操纵子相反。cyn操纵子的基因和cynR基因已被克隆、测序并过量表达。浓度约为1 mM的氰酸盐对缺乏氰酸酶基因的大肠杆菌菌株有毒，但其中存在氰酸酶诱导基因的菌株可以在高达20 mM浓度的氰酸盐作为唯一氮源的情况下生长。氰酸酶本身的存在不足以克服氰酸盐毒性——通透酶也必须存在。缺乏氰酸酶基因但具有功能性通透酶基因的菌株对氰酸盐极其敏感。氰酸盐的摄取涉及通透酶基因的产物，是一个能量依赖过程。看来cyn操纵子已经进化为在解毒/分解来自细胞内和细胞外来源的氰酸盐方面发挥作用。
