Nijkamp H J
J Bacteriol. 1969 Nov;100(2):585-93. doi: 10.1128/jb.100.2.585-593.1969.
Derepression of the synthesis of inosine 5'-monophosphate (IMP) dehydrogenase and of xanthosine 5'-monophosphate (XMP) aminase in pur mutants of Escherichia coli which are blocked in the biosynthesis of adenine nucleotides and guanine nucleotides differs in two ways from derepression in pur mutants blocked exclusively in the biosynthesis of guanine nucleotides. (i) The maximal derepression is lower, and (ii) a sharp decrease in the specific activities of AMP dehydrogenase and XMP aminase occurs, following maximal derepression. From the in vivo and in vitro experiments described, it is shown that the lack of adenine nucleotides in derepressed pur mutants blocked in the biosynthesis of adenine and guanine nucleotides is responsible for these two phenomena. The adenine nucleotides are shown to play an important regulatory role in the biosynthesis of guanosine 5'-monophosphate (GMP). (i) They induce the syntheses of IMP dehydrogenase and XMP aminase. (The mechanism of induction may involve the expression of the gua operon.) (ii) They appear to have an activating function in IMP dehydrogenase and XMP aminase activity. The physiological importance of these regulatory characteristics of adenine nucleotides in the biosynthesis of GMP is discussed.
在腺嘌呤核苷酸和鸟嘌呤核苷酸生物合成中受阻的大肠杆菌嘌呤突变体中，肌苷5'-单磷酸（IMP）脱氢酶和黄苷5'-单磷酸（XMP）氨基酶合成的去阻遏，在两个方面不同于仅在鸟嘌呤核苷酸生物合成中受阻的嘌呤突变体中的去阻遏。（i）最大去阻遏较低，并且（ii）在最大去阻遏之后，AMP脱氢酶和XMP氨基酶的比活性急剧下降。从所描述的体内和体外实验表明，在腺嘌呤和鸟嘌呤核苷酸生物合成中受阻的去阻遏嘌呤突变体中腺嘌呤核苷酸的缺乏是这两种现象的原因。腺嘌呤核苷酸在鸟苷5'-单磷酸（GMP）生物合成中起着重要的调节作用。（i）它们诱导IMP脱氢酶和XMP氨基酶的合成。（诱导机制可能涉及gua操纵子的表达。）（ii）它们似乎在IMP脱氢酶和XMP氨基酶活性中具有激活功能。讨论了腺嘌呤核苷酸的这些调节特性在GMP生物合成中的生理重要性。
