Beckner S K, Blecher M
Biochim Biophys Acta. 1981 Apr 3;673(4):477-86. doi: 10.1016/0304-4165(81)90479-7.
Cholera toxin catalyzed the ADP-ribosylation of a single plasma membrane protein (Mr 55 000) of both RL-PR-C rat hepatocytes and purified rat liver plasma membranes. Labeling of this protein from nicotinamide [2,8-3H]adenine dinucleotide was competitively inhibited by free arginine, but by no other amino acid tested, including lysine. The same protein was ADP-ribosylated from NAD+ endogenously, i.e., in the absence of toxin. This process was, however, not competitively inhibited by added arginine nor by any other amino acid tested lysine. Free ADP-ribose, even in 50-fold molar excess over the nicotinamide [2,8-3H]adenine dinucleotide substrate, did not reduce (by isotope dilution) the endogenous or cholera toxin-catalyzed labeling of the 55 000 dalton membrane protein. It is likely, therefore, that hepatocyte plasma membranes contain an ADP-ribosyltransferase, with a mechanism similar to that of the A subunit of cholera toxin, in that both transfer ADP-ribose to the same membrane protein and in that neither apparently produce free ADP-ribose as an intermediate. It is also clear that the acceptor residue in the 55 000 dalton protein is different for each process. Cholera toxin-catalyzed and endogenous transfer of ADP-ribose to the hepatocyte plasma membrane protein, in contrast to a pigeon erythrocyte system, required no cytosolic factors. The results indicate that ADP-ribosylation in cloned differentiated rat hepatocytes differs from that in pigeon erythrocytes in that the acceptor protein is larger (55 000 compared to 42 000 daltons), cytosolic factors are not required and transfer of ADP-ribose to the acceptor protein occurs endogenously.
霍乱毒素催化RL-PR-C大鼠肝细胞和纯化的大鼠肝细胞膜中单一质膜蛋白（分子量55000）的ADP核糖基化。来自烟酰胺[2,8-³H]腺嘌呤二核苷酸对该蛋白的标记受到游离精氨酸的竞争性抑制，但不受包括赖氨酸在内的其他任何测试氨基酸的抑制。同一蛋白可从NAD⁺进行内源性ADP核糖基化，即在没有毒素的情况下。然而，该过程不受添加的精氨酸或任何其他测试氨基酸（包括赖氨酸）的竞争性抑制。即使游离ADP核糖的摩尔量比烟酰胺[2,8-³H]腺嘌呤二核苷酸底物高50倍，也不会（通过同位素稀释）减少55000道尔顿膜蛋白的内源性或霍乱毒素催化的标记。因此，肝细胞质膜可能含有一种ADP核糖基转移酶，其机制与霍乱毒素A亚基的机制相似，因为两者都将ADP核糖转移到同一膜蛋白上，且两者显然都不产生游离ADP核糖作为中间体。同样明显的是，55000道尔顿蛋白中的受体残基在每个过程中是不同的。与鸽红细胞系统相比，霍乱毒素催化的以及内源性的ADP核糖向肝细胞质膜蛋白的转移不需要胞质因子。结果表明，克隆的分化大鼠肝细胞中的ADP核糖基化与鸽红细胞中的不同，在于受体蛋白更大（55000道尔顿相比于42000道尔顿），不需要胞质因子，并且ADP核糖向受体蛋白的转移是内源性发生的。
