McFadden P N, Horwitz J, Clarke S
Biochem Biophys Res Commun. 1983 Jun 15;113(2):418-24. doi: 10.1016/0006-291x(83)91742-4.
Protein carboxyl methyltransferase activity (S-adenosyl-L-methionine: protein carboxyl-0-methyltransferase; E.C. 2.1.1.24) has been detected in crude soluble extracts of cow eye lens. The activity incorporates methyl groups from S-adenosyl-L-methionine into endogenous lens proteins in vitro, and several of these species co-migrate electrophoretically with lens crystallins. A 2600-fold purification of the enzyme free of endogenous substrates was achieved by gel filtration and affinity chromatography. The lens methyltransferase has a native molecular weight of approximately 27,000, and catalyzes the substoichiometric incorporation of highly alkali-labile methyl ester groups into a broad range of protein substrates. The lens enzyme appears to be similar to that found in human erythrocytes, which specifically recognizes and modifies D-aspartic acid residues in aged proteins in a postulated degradative or racemization-repair pathway (McFadden, P.N., and Clarke, S. (1982) Proc. Natl. Acad. Sci. U.S.A. 79, 2460-2464).
在牛眼晶状体的粗可溶性提取物中检测到了蛋白质羧基甲基转移酶活性（S-腺苷-L-甲硫氨酸：蛋白质羧基-O-甲基转移酶；E.C. 2.1.1.24）。该活性在体外将S-腺苷-L-甲硫氨酸中的甲基掺入内源性晶状体蛋白中，其中有几种蛋白在电泳时与晶状体晶状体蛋白共迁移。通过凝胶过滤和亲和色谱法实现了该酶的2600倍纯化，且不含内源性底物。晶状体甲基转移酶的天然分子量约为27,000，并催化将高度碱不稳定的甲酯基团亚化学计量地掺入多种蛋白质底物中。晶状体酶似乎与人红细胞中的酶相似，后者在假定的降解或消旋化-修复途径中特异性识别并修饰老化蛋白质中的D-天冬氨酸残基（McFadden, P.N., and Clarke, S. (1982) Proc. Natl. Acad. Sci. U.S.A. 79, 2460 - 2464）。
