Kamiński Z W, Jezewska M M
Biochem J. 1981 Dec 15;200(3):597-603. doi: 10.1042/bj2000597.
The course of the reaction sequence hypoxanthine leads to xanthine leads to uric acid, catalysed by the NAD+-dependent activity of xanthine oxidoreductase, was investigated under conditions either of immediate oxidation of the NADH formed or of NADH accumulation. The enzymic preparation was obtained from rat liver, and purified 75-fold (as compared with the 25000 g supernatant) on a 5'-AMP-Sepharose 4B column; in this preparation the NAD+-dependent activity accounted for 100% of total xanthine oxidoreductase activity. A spectrophotometric method was developed for continuous measurements of changes in the concentrations of the three purines involved. The time course as well as the effects of the concentrations of enzyme and of hypoxanthine were examined. NADH produced by the enzyme lowered its activity by 50%, resulting in xanthine accumulation and in decreases of uric acid formation and of hypoxanthine utilization. The inhibition of the Xanthine oxidoreductase NAD+-dependent activity by NADH is discussed as a possible factor in the regulation of IMP biosynthesis by the 'de novo' pathway or (from unchanged hypoxanthine) by ther salvage pathway.
研究了在NADH即时氧化或NADH积累的条件下，由黄嘌呤氧化还原酶的NAD⁺依赖性活性催化的反应序列：次黄嘌呤生成黄嘌呤再生成尿酸的过程。酶制剂取自大鼠肝脏，并在5'-AMP-Sepharose 4B柱上纯化了75倍（与25000g上清液相比）；在该制剂中，NAD⁺依赖性活性占黄嘌呤氧化还原酶总活性的100%。开发了一种分光光度法，用于连续测量所涉及的三种嘌呤浓度的变化。研究了时间进程以及酶浓度和次黄嘌呤浓度的影响。酶产生的NADH使其活性降低了50%，导致黄嘌呤积累，尿酸生成和次黄嘌呤利用减少。讨论了NADH对黄嘌呤氧化还原酶NAD⁺依赖性活性的抑制作用，这可能是“从头”途径或（由未改变的次黄嘌呤）补救途径调节IMP生物合成的一个因素。
