Stauffer G V, Baker C A, Brenchley J E
J Bacteriol. 1974 Dec;120(3):1017-25. doi: 10.1128/jb.120.3.1017-1025.1974.
The regulation of serine transhydroxymethylase (EC 2.1.2.1.; l-serine:tetrahydrofolic-5,10-hydroxymethyltransferase) has been investigated in Salmonella typhimurium LT2. Our results indicate that limitation of a methionine auxotroph for methionine does not cause derepression of this enzyme as reported for Escherichia coli. However, a sixfold decrease in specific activity was observed when S. typhimurium cells were grown in glucose minimal medium supplemented with serine, glycine, methionine, adenine, guanine, and thymine. None of these compounds added to the growth medium individually produced more than a 42% reduction of wild-type enzyme activity. This enhanced repression by the combination of compounds suggests a form of cumulative repression of this enzyme. Growth of serine and thymine auxotrophs, with the respective requirement of each limiting, did not result in increased enzyme activity. However, growth of a purine auxotroph with a limiting amount of either guanine or inosine resulted in a five- to sevenfold increase in enzyme activity. A second condition causing significant derepression (fourfold increase) above the levels observed with cells grown in minimal medium was the addition of 0.5 mug of trimethoprim per ml, an inhibitor of the dihydrofolate reductase activity. (A partial report on this work was presented at 1974 meeting of the American Society for Microbiology.)
已对鼠伤寒沙门氏菌LT2中的丝氨酸转羟甲基酶（EC 2.1.2.1；L-丝氨酸：四氢叶酸-5,10-羟甲基转移酶）的调控进行了研究。我们的结果表明，甲硫氨酸营养缺陷型对甲硫氨酸的限制并不会像对大肠杆菌所报道的那样导致该酶的去阻遏。然而，当鼠伤寒沙门氏菌细胞在补充了丝氨酸、甘氨酸、甲硫氨酸、腺嘌呤、鸟嘌呤和胸腺嘧啶的葡萄糖基本培养基中生长时，观察到比活性下降了六倍。单独添加到生长培养基中的这些化合物均未使野生型酶活性降低超过42%。这些化合物组合导致的这种增强的阻遏表明了该酶的一种累积阻遏形式。丝氨酸和胸腺嘧啶营养缺陷型在各自所需物质受限的情况下生长，并未导致酶活性增加。然而，嘌呤营养缺陷型在鸟嘌呤或肌苷含量受限的情况下生长，导致酶活性增加了五至七倍。另一个导致比在基本培养基中生长的细胞所观察到的水平显著去阻遏（增加四倍）的条件是每毫升添加0.5微克甲氧苄啶，这是二氢叶酸还原酶活性的抑制剂。（关于这项工作的部分报告在1974年美国微生物学会会议上发表。）
