Zannis V I, Gudas L J, Martin D W
Biochem Genet. 1980 Feb;18(1-2):1-19. doi: 10.1007/BF00504356.
Hypoxanthine-guanine phosphoribosyltransferase is a ubiquitous human enzyme, the inherited deficiency of which leads to a specific metabolic-neurological syndrome. Native acrylamide isoelectric focusing revealed that the human enzyme consists of different numbers of isoenzymes depending on the tissue of origin. The erythrocytic enzyme has the most isoenzymes while the enzyme from cultured fibroblasts has only a single isoenzyme. The isoenzyme pattern of the erythrocytic enzyme changes on storage of the crude hemolysate at 4 C. Treatment of the stored crude hemolysate with 4.5 M urea and 0.35 mM beta-mercaptoethanol results in an isoenzyme pattern similar to that of the fresh crude extract. Thus the additional isoenzymes are generated on storage not by covalent modification of the enzyme but probably by binding of small molecules to the enzyme or to association of the enzyme molecules. Hypoxanthine-guanine phosphoribosyltransferase has been purified to 80% homogeneity in three steps, DEAE Sephadex chromatography, heat treatment at 85 C for 5 min, and hydroxylapatite chromatography. Denaturing two-dimensional gel electrophoresis of the erythrocytic enzyme revealed that the erythrocytic enzyme is composed of three major types of subunits (1-3) with the same molecular weight but different isoelectric points. In contrast, the fibroblast enzyme is composed of only a single type of subunit, which comigrates with subunit 1 of the erythrocytic enzyme. Since there is a single genetic locus in humans for HGPRTase (the enzyme is X linked) (Nyhan et al., 1967), the observed subunit modification of the erythrocyte enzyme appears to be the result of posttranslational modification. These findings provide a simple explanation for the observed electrophoretic properties of human HGPRTase. A patient with 0.5% of HGPRTase activity in his erythrocytes was found to have small amounts (greater than 0.5% but less than 5% of normal) of the erythrocytic HGPRTase subunits.
次黄嘌呤 - 鸟嘌呤磷酸核糖转移酶是一种广泛存在于人体的酶，其遗传性缺乏会导致一种特定的代谢 - 神经综合征。天然丙烯酰胺等电聚焦显示，根据酶的来源组织不同，人体中的这种酶由不同数量的同工酶组成。红细胞中的酶同工酶数量最多，而培养的成纤维细胞中的酶只有一种同工酶。将粗制溶血产物在4℃储存时，红细胞酶的同工酶模式会发生变化。用4.5 M尿素和0.35 mMβ-巯基乙醇处理储存后的粗制溶血产物，会得到与新鲜粗提物相似的同工酶模式。因此，储存时产生的额外同工酶不是通过酶的共价修饰，而是可能通过小分子与酶的结合或酶分子的缔合产生的。通过三步纯化，即DEAE葡聚糖凝胶层析、85℃热处理5分钟和羟基磷灰石层析，次黄嘌呤 - 鸟嘌呤磷酸核糖转移酶已达到80%的纯度。红细胞酶的变性二维凝胶电泳显示，红细胞酶由三种主要类型的亚基（1 - 3）组成，分子量相同但等电点不同。相比之下，成纤维细胞酶仅由一种亚基组成，它与红细胞酶的亚基1迁移率相同。由于人类次黄嘌呤 - 鸟嘌呤磷酸核糖转移酶（该酶是X连锁的）（尼汉等人，1967年）只有一个基因位点，红细胞酶中观察到的亚基修饰似乎是翻译后修饰的结果。这些发现为观察到的人类次黄嘌呤 - 鸟嘌呤磷酸核糖转移酶的电泳特性提供了一个简单的解释。发现一名红细胞中次黄嘌呤 - 鸟嘌呤磷酸核糖转移酶活性为0.5%的患者，其红细胞次黄嘌呤 - 鸟嘌呤磷酸核糖转移酶亚基含量较少（大于正常水平的0.5%但小于5%）。
