Becker M A
Biochim Biophys Acta. 1976 Jun 18;435(2):132-44. doi: 10.1016/0005-2787(76)90244-6.
Incubation of normal and hypoxanthine-guanine phosphoribosyltransferase-deficient (mutant) human fibroblasts with inosine results in increased intracellular concentration of 5-phosphoribosyl 1-pyrophosphate (PP-ribose-P). The magnitude of this increase is dependent on the concentration of the nucleoside and results from donation of the ribose moiety of inosine to the ribosyl phosphate moiety of PP-ribose-P through ribose phosphate intermediates. During incubation, rates of purine nucleotide synthesis de novo, estimated by incorporation of (14C) formate into formylglycinamide ribotide, are diminished in both normal and mutant cells: 5 mM inosine inhibits purine synthesis by 60-80% in normal cells and 2-20% in hypoxanthine-guanine phosphoribosyltransferase-deficient cells. The rates of purine synthesis in both normal and mutant cells are increased, however, during incubation with methylene blue at concentrations (50-100 muM) which result in more modest increases in ribose 5-phosphate and PP-ribose-P concentrations than are observed with inosine. Saturation of the PP-ribose-P amidotransferase reaction by PP-ribose-P does not appear, therefore, to explain the failure of increased PP-ribose-P concentration to stimulate the rate of purine synthesis in either type of fibroblast during incubation with inosine. Although the dissociation between PP-ribose-P concentration and the rate of purine nucleotide synthesis in normal fibroblasts incubated with inosine may be explained at least in part by an accompanying increase in intracellular concentrations of purine nucleotide feedback inhibitors, purine nucleotide concentrations are unchanged in mutant cells during incubation with inosine; these cells, in addition, show minimal (less than 3% of normal) incorporation of labeled hypoxanthine or the hypoxanthine moiety of inosine into purine nucleotides. The effect of inosine on purine synthesis de novo in hypoxanthine-guanine phosphoribosyltransferase-deficient fibroblasts is not explained in full by consideration of the concentrations of purine nucleotides and of PP-ribose-P, the factors frequently invoked as antagonistic regulators controlling the rate of this process.
将正常的和次黄嘌呤 - 鸟嘌呤磷酸核糖转移酶缺陷型（突变型）人成纤维细胞与肌苷一起温育，会导致细胞内5 - 磷酸核糖1 - 焦磷酸（PP - 核糖 - P）的浓度升高。这种升高的幅度取决于核苷的浓度，是通过磷酸核糖中间体将肌苷的核糖部分捐赠给PP - 核糖 - P的核糖磷酸部分而产生的。在温育过程中，通过将（14C）甲酸掺入甲酰甘氨酰胺核糖核苷酸来估计的嘌呤核苷酸从头合成速率，在正常细胞和突变细胞中均降低：5 mM肌苷在正常细胞中抑制嘌呤合成60 - 80%，在次黄嘌呤 - 鸟嘌呤磷酸核糖转移酶缺陷型细胞中抑制2 - 20%。然而，在与亚甲蓝一起温育期间，正常细胞和突变细胞中的嘌呤合成速率均增加，亚甲蓝的浓度（50 - 100 μM）导致核糖5 - 磷酸和PP - 核糖 - P浓度的增加幅度比肌苷引起的增加幅度小。因此，PP - 核糖 - P对PP - 核糖 - P酰胺转移酶反应的饱和似乎并不能解释在与肌苷一起温育期间，PP - 核糖 - P浓度升高未能刺激任何一种类型的成纤维细胞中嘌呤合成速率的原因。尽管在与肌苷一起温育的正常成纤维细胞中，PP - 核糖 - P浓度与嘌呤核苷酸合成速率之间的解离至少可以部分地由细胞内嘌呤核苷酸反馈抑制剂浓度的伴随增加来解释，但在与肌苷一起温育期间，突变细胞中的嘌呤核苷酸浓度没有变化；此外，这些细胞将标记的次黄嘌呤或肌苷的次黄嘌呤部分掺入嘌呤核苷酸的量极少（不到正常量的3%）。仅考虑嘌呤核苷酸和PP - 核糖 - P的浓度（这些因素经常被认为是控制这一过程速率的拮抗调节因子），并不能完全解释肌苷对次黄嘌呤 - 鸟嘌呤磷酸核糖转移酶缺陷型成纤维细胞中嘌呤从头合成的影响。
