Szewczuk A, Connell G E
Can J Biochem. 1975 Jun;53(6):706-12. doi: 10.1139/o75-097.
Using the phthaloyl method, 18 gamma-L-glutamyl peptides labelled with 14-C in the N-terminal position have been synthesized. The products were isolated by simple procedures using a Dowex-1 column or high voltage electrophoresis. The synthetic peptides contain minor impurities of the corresponding D-glutamyl isomers. The proportion of D-isomer was determined by the use of glutamic decarboxylase, or by a new method using digestion with purified gamma-glutamyl cyclotransferase and determination of the resulting 2-pyrrolidone-5-carboxylic acid (5-oxoproline). Evidence was obtained that gamma-glutamyl cyclotransferase acts only on the L-form of gamma-glutamyl substrates; the enzyme could, therefore, be used for preparation of gamma-D-glutamyl peptides from their racemic mixtures. The specificity of gamma-glutamyl cyclotransferase has been examined using pure enzyme prepared from pig liver, and extracts from tissues of rat and man. The basic structural requirement in substrates may be represented as gamma-L-glutamyl-NH--CHR--COOH. The amino acid linked to the gamma-glutamyl group must be in the L configuration.
采用邻苯二甲酰法，合成了18种在N端位置用14-C标记的γ-L-谷氨酰肽。产物通过使用Dowex - 1柱或高压电泳的简单程序进行分离。合成肽含有相应D-谷氨酰异构体的少量杂质。D-异构体的比例通过使用谷氨酸脱羧酶或一种新方法来确定，该新方法是用纯化的γ-谷氨酰环转移酶消化并测定生成的2-吡咯烷酮-5-羧酸（5-氧代脯氨酸）。有证据表明γ-谷氨酰环转移酶仅作用于γ-谷氨酰底物的L型；因此，该酶可用于从其外消旋混合物制备γ-D-谷氨酰肽。已使用从猪肝制备的纯酶以及大鼠和人组织的提取物研究了γ-谷氨酰环转移酶的特异性。底物中的基本结构要求可表示为γ-L-谷氨酰-NH--CHR--COOH。与γ-谷氨酰基团相连的氨基酸必须为L构型。
