EVIDENCE FOR B12-DEPENDENT ENZYME ETHANOLAMINE DEAMINASE IN SALMONELLA
EVIDENCE FOR B12-DEPENDENT ENZYME ETHANOLAMINE DEAMINASE IN SALMONELLA
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DOI：
10.1038/254150a0
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发表时间：
1975-01-01
期刊：
影响因子：
64.8
通讯作者：
CHANG, JT
中科院分区：
文献类型：
--
作者：
CHANG, GW;CHANG, JT
肠道细菌大肠杆菌和鼠伤寒沙门氏菌和人类一样，不能合成大量的钴胺素（B12）化合物，因此它们依赖于外源性维生素B12的酶。快乐。coliandS。鼠伤寒杆菌是唯一报道的b12依赖酶，它催化蛋氨酸生物合成的最后一步——同型半胱氨酸甲基化生成蛋氨酸。然而，这些细菌不依赖于外源的b12来生长，因为它们有一种替代的不依赖于b12的同型半胱氨酸转甲基化酶（非b12酶）可以催化相同的反应。非B12转甲基化酶的效率远低于相应的B12依赖酶：在缺乏维生素B12的细菌中生长，非B12依赖酶占可溶性蛋白总量的3 - 5% 2。如果这种酶被突变阻断，突变细菌要么需要蛋氨酸本身，要么需要外源性B12，这使得它们能够利用依赖B12的酶进行蛋氨酸生物合成3。我们已经寻找了其他依赖b12的酶inS。鼠伤寒发现了乙醇胺脱氨酶存在的证据。我们没有发现其他平行的非b12依赖性和b12依赖性酶inS的例子。typhimurium.E。大肠杆菌似乎也有乙醇胺脱氨酶。
THE enteric bacteriaEscherichia coliandSalmonella typhimurium, like man, do not synthesise significant amounts of cobalamin (B12) compounds and thus depend on exogenous vitamin B12for their B12-dependent enzymes1. InE. coliandS. typhimuriumthe only reported B12-dependent enzyme catalyses the final step in methionine biosynthesis—the methylation of homocysteine to give methionine. These bacteria do not depend on exogenous B12for growth, however, for they have an alternative B12-independent homocysteine transmethylase (non-B12enzyme) which can catalyse the same reaction. The non-B12transmethylase is much less efficient than the corresponding B12-dependent enzyme: in bacteria grown in the absence of vitamin B12, the non-B12-dependent enzyme comprises 3–5 % of the total soluble protein2. If this enzyme is blocked by mutation, the mutant bacteria require either methionine itself or exogenous B12, which allows them to utilise the B12-dependent enzyme for methionine biosynthesis3. We have sought other B12-dependent enzymes inS. typhimuriumand found evidence for an ethanolamine deaminase. We did not find other examples of parallel non-B12-dependent and B12-dependent enzymes inS. typhimurium.E. colialso seems to have an ethanolamine deaminase.