Lai C Y, Xia Q C, Salotra P T
Biochem Biophys Res Commun. 1983 Oct 14;116(1):341-8. doi: 10.1016/0006-291x(83)90420-5.
Renatured, S-carboxymethylated subunit A1 of cholera toxin possess the ADP-ribose transferase activity (Lai, et.al., Biochem. Biophys. Res. Commun. 1981, 102, 1021). In the absence of acceptor self ADP-ribosylation of A1 subunit was observed. Stoicheometric incorporation of ADP-ribose moiety was achieved in 20 min at room temperature in a 0.1 - 0.2M PO4(Na) buffer, pH 6.6. On incubation of the complex with polyarginine, 75% of the enzyme-bound ADP-ribose moiety was transferred to the acceptor in 25 min. The ADP-ribosylated A1 was stable at low pH, and on cleavage with BrCN, the ADP-ribose moiety was found associated with peptide Cn I, the COOH-terminal fragment of A1 subunit. On further fragmentation with cathepsin D, a dodecapeptide containing ADP-ribose moiety was isolated whose structure was determined as: Asp-Glu-Glu-Leu-His-Arg-Gly-Tyr-Arg*-Asp-Arg-Tyr. The Arg* in the peptide was indicated to be the site of ADP-ribosylation.
复性的霍乱毒素S-羧甲基化A1亚基具有ADP-核糖转移酶活性（赖等人，《生物化学与生物物理研究通讯》，1981年，102卷，第1021页）。在没有受体的情况下，观察到A1亚基的自身ADP-核糖基化。在室温下，于pH 6.6的0.1 - 0.2M磷酸钠（Na）缓冲液中，20分钟内实现了ADP-核糖部分的化学计量掺入。将该复合物与聚精氨酸一起温育时，25分钟内75%的酶结合ADP-核糖部分转移到了受体上。ADP-核糖基化的A1在低pH下稳定，用溴化氰裂解后，发现ADP-核糖部分与肽Cn I相关，Cn I是A1亚基的COOH末端片段。用组织蛋白酶D进一步裂解后，分离出了一个含有ADP-核糖部分的十二肽，其结构确定为：天冬氨酸-谷氨酸-谷氨酸-亮氨酸-组氨酸-精氨酸-甘氨酸-酪氨酸-精氨酸*-天冬氨酸-精氨酸-酪氨酸。该肽中的精氨酸*被认为是ADP-核糖基化的位点。
