Simon R D
Biochim Biophys Acta. 1976 Feb 13;422(2):407-18. doi: 10.1016/0005-2744(76)90151-0.
The cyanobacteria produce multi-L-arginyl-poly (aspartic acid), a high molecular weight (Mr=25 000-125 000) branched polypeptide consisting of a poly(aspartic acid) core with L-arginyl residues peptide bonded to each free carboxyl group of the poly(aspartic acid). An enzyme which will elongate Arg-poly(Asp) has been isolated and purified 92-fold from the filamentous cyanobacterium Anabaena cylindrica. The enzyme incorporates arginine and aspartic acid into Arg-poly(Asp) in a reaction which requires ATP, KCl, MgCl2, and a sulfhydryl reagent. The enzymatic incorporation of arginine is dependent upon the presence of L-aspartic acid but not visa versa, a finding which suggests the order of amino acid addition to the branched polypeptide-aspartic acid is added to the core followed by the attachment of an arginine branch. The elongation of Arg-poly(Asp) in-vitro is insensitive to the addition of protein synthesis inhibitors and to the addition of nucleases. These findings support the notion previosly suggested from in-vivo studies that Arg-poly(Asp) is synthesized via a non-ribosomal route and also demonstrate that amino-acetylated transfer-RNAs play no part in at least one step of the biosynthetic mechanism.
蓝细菌产生多-L-精氨酰-聚（天冬氨酸），一种高分子量（Mr=25000-125000）的分支多肽，它由一个聚（天冬氨酸）核心组成，L-精氨酰残基通过肽键连接到聚（天冬氨酸）的每个游离羧基上。一种能使精氨酰-聚（天冬氨酸）延长的酶已从丝状蓝细菌圆柱鱼腥藻中分离并纯化了92倍。该酶在一个需要ATP、KCl、MgCl2和一种巯基试剂的反应中，将精氨酸和天冬氨酸掺入精氨酰-聚（天冬氨酸）中。精氨酸的酶促掺入依赖于L-天冬氨酸的存在，但反之则不然，这一发现表明向分支多肽添加氨基酸的顺序——天冬氨酸先添加到核心上，随后连接一个精氨酸分支。精氨酰-聚（天冬氨酸）的体外延长对添加蛋白质合成抑制剂和核酸酶不敏感。这些发现支持了之前体内研究提出的观点，即精氨酰-聚（天冬氨酸）是通过非核糖体途径合成的，并且还证明氨基乙酰化的转移RNA在生物合成机制的至少一个步骤中不起作用。
