A PHYSIOLOGICAL-ROLE FOR CYANATE-INDUCED CARBONIC-ANHYDRASE IN ESCHERICHIA-COLI
A PHYSIOLOGICAL-ROLE FOR CYANATE-INDUCED CARBONIC-ANHYDRASE IN ESCHERICHIA-COLI
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DOI：
10.1128/jb.175.5.1443-1451.1993
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发表时间：
1993-03-01
影响因子：
3.2
通讯作者：
FUCHS, JA
中科院分区：
文献类型：
--
作者：
GUILLOTON, MB;LAMBLIN, AF;FUCHS, JA
氰酸盐诱导大肠杆菌中cyn操纵子的表达。cyn操纵子包括cyn基因，编码氰化酶，该酶催化氰酸盐与碳酸氢盐的反应产生氨和二氧化碳。最近发现一种碳酸酐酶活性由cyn操纵子的第一个基因cynT基因编码；有人提出，碳酸酐酶在氰酸盐分解过程中防止碳酸氢盐的消耗，因为细胞外扩散损失了二氧化碳（M. B. Guilloton， J. J. Korte， A. F. Lamblin， J. A. Fuchs，和P. M. Anderson， J. Biol）。化学。267:3731-3734,1992)。该操纵子的第三个基因产物cynX的功能尚不清楚。在这里报道的研究中，通过构建染色体突变体来研究cynT和cynX的生理作用，其中这三个基因中的每一个都变得不活跃。DELTAcynT染色体突变体表达活性氰化酶，但不表达活性碳酸酐酶。与野生型菌株相比，DELTAcynT菌株的生长受到氰酸盐的抑制，突变菌株在0.03%（空气）的CO2分压（pCO2）下生长时不能降解氰酸盐，因此不能以氰酸盐作为唯一的氮源。然而，在高co2浓度（3%）下，DELTAcynT菌株的表现与野生型菌株相似；它对氰酸盐的毒性作用不敏感，可以降解氰酸盐，并以氰酸盐作为唯一的氮源进行生长。这些结果与碳酸酐酶的功能一致。携带cynS::kan的染色体突变体表达诱导的碳酸酐酶活性，但不表达活性的氰化酶。在低PCO2条件下，cynS:: kan突变体对氰酸盐的敏感性远低于DELTAcyn T突变体，这表明由氰化酶催化的碳酸氢盐与氰酸盐反应引起的碳酸氢盐消耗比氰酸盐直接抑制对生长的危害更大。携带无功能cynX基因的突变体（cynX:: kan和DELTAcynT cynX:: kan）与亲本菌株在氰酸盐敏感性、碳酸酐酶和氰化酶的存在或整个细胞对氰酸盐的降解方面没有区别；cynX产物的生理作用尚不清楚。
Cyanate induces expression of the cyn operon in Escherichia coli. The cyn operon includes the gene cynS, encoding cyanase, which catalyzes the reaction of cyanate with bicarbonate to give ammonia and carbon dioxide. A carbonic anhydrase activity was recently found to be encoded by the cynT gene, the first gene of the cyn operon; it was proposed that carbonic anhydrase prevents depletion of bicarbonate during cyanate decomposition due to loss of CO2 by diffusion out of the cell (M. B. Guilloton, J. J. Korte, A. F. Lamblin, J. A. Fuchs, and P. M. Anderson, J. Biol. Chem. 267:3731-3734, 1992). The function of the product of the third gene of this operon, cynX, is unknown. In the study reported here, the physiological roles of cynT and cynX were investigated by construction of chromosomal mutants in which each of the three genes was rendered inactive. The DELTAcynT chromosomal mutant expressed an active cyanase but no active carbonic anhydrase. In contrast to the wild-type strain, the growth of the DELTAcynT strain was inhibited by cyanate, and the mutant strain was unable to degrade cyanate and therefore could not use cyanate as the sole nitrogen source when grown at a partial CO2 pressures (pCO2) of 0.03% (air). At a high pCO2 (3%), however, the DELTAcynT strain behaved like the wild-type strain; it was significantly less sensitive to the toxic effects of cyanate and could degrade cyanate and use cyanate as the sole nitrogen source for growth. These results are consistent with the proposed function for carbonic anhydrase. The chromosomal mutant carrying cynS::kan expressed induced carbonic anhydrase activity but no active cyanase. The cynS:: kan mutant was found to be much less sensitive to cyanate than the DELTAcyn T mutant at a low PCO2, indicating that bicarbonate depletion due to the reaction of bicarbonate with cyanate catalyzed by cyanase is more deleterious to growth than direct inhibition by cyanate. Mutants carrying a nonfunctional cynX gene (cynX:: kan and DELTAcynT cynX:: kan) did not differ from the parental strains with respect to cyanate sensitivity, presence of carbonic anhydrase and cyanase, or degradation of cyanate by whole cells; the physiological role of the cynX product remains unknown.