Kelln R A, Kinahan J J, Foltermann K F, O'Donovan G A
J Bacteriol. 1975 Nov;124(2):764-74. doi: 10.1128/jb.124.2.764-774.1975.
The repressive effects of exogenous cytidine on growing cells was examined in a specially constructed strain in which the pool sizes of endogenous uridine 5'-diphosphate and uridine 5'-triphosphate cannot be varied by the addition of uracil and/or uridine to the medium. Five enzymes of the pyrimidine biosynthetic pathway and one enzyme of the arginine biosynthetic pathway were assayed from cells grown under a variety of conditions. Cytidine repressed the synthesis of dihydroorotase (encoded by pyrC), dihydroorotate dehydrogenase (encoded by pyrD), and ornithine transcarbamylase (encoded by argI). Moreover, aspartate transcarbamylase (encoded by pyrB) became further derepressed upon cytidine addition, whereas no change occurred in the levels of the last two enzymes (encoded by pyrE and pyrF) of the pyrimidine pathway. Quantitative nucleotide pool determinations have provided evidence that any individual ribo- or deoxyribonucleoside mono-, di-, or triphosphate of cytosine or uracil is not a repressing metabolite for the pyrimidine biosynthetic enzymes. Other nucleotide derivatives or ratios must be considered.
在一个特别构建的菌株中检测了外源性胞苷对生长细胞的抑制作用，在该菌株中，通过向培养基中添加尿嘧啶和/或尿苷无法改变内源性尿苷5'-二磷酸和尿苷5'-三磷酸的库大小。从在各种条件下生长的细胞中检测了嘧啶生物合成途径的五种酶和精氨酸生物合成途径的一种酶。胞苷抑制二氢乳清酸酶（由pyrC编码）、二氢乳清酸脱氢酶（由pyrD编码）和鸟氨酸转氨甲酰酶（由argI编码）的合成。此外，添加胞苷后天冬氨酸转氨甲酰酶（由pyrB编码）进一步去阻遏，而嘧啶途径的最后两种酶（由pyrE和pyrF编码）的水平没有变化。定量核苷酸库测定提供了证据，表明胞嘧啶或尿嘧啶的任何单个核糖或脱氧核糖核苷单磷酸、二磷酸或三磷酸都不是嘧啶生物合成酶的抑制性代谢物。必须考虑其他核苷酸衍生物或比率。
