Osterhout J J, Lax S R, Ravel J M
J Biol Chem. 1983 Jul 10;258(13):8285-9.
Two factors have been isolated from wheat germ that enhance the ability of initiation factor 2(eIF-2) to form a ternary complex with GTP and Met-tRNAf. One of these factors, Co-eIF-2 beta, is a monomeric protein with a molecular weight of approximately 83,000 (Lax, S. R., Osterhout, J.J., and Ravel, J.M. (1982) J. Biol. Chem. 257, 8233-8237). The purification and properties of Co-eIF-2 alpha are described in this report. The most highly purified preparations of Co-eIF-2 alpha contain two polypeptides with molecular weights of 21,000 and 19,000. Both Co-eIF-2 alpha and Co-eIF-2 beta are heat-stable factors that stimulate ternary complex formation in the presence and absence of Mg2+ and overcome the inhibitory effect of aurintricarboxylic acid. Co-eIF-2 alpha differs from Co-eIF-2 beta in that Co-eIF-2 beta stimulates the formation of a binary complex between eIF-2 and GDP and Co-eIF-2 alpha does not. Also. The stimulatory effects of Co-eIF-2 alpha and Co-eIF-2 beta on the ternary complex formation are close to additive, strongly suggesting that the two factors function independently. Neither Co-eIF-2 alpha nor Co-eIF-2 beta enhances the rate of exchange between GDP bound to eIF-2 and free GDP, indicating that neither factor functions as a guanine nucleotide exchange factor.
从小麦胚芽中分离出了两种因子，它们能增强起始因子2（eIF-2）与GTP和甲硫氨酰-tRNAf形成三元复合物的能力。其中一种因子，协同eIF-2β，是一种分子量约为83,000的单体蛋白（拉克斯，S.R.，奥斯特豪特，J.J.，和拉韦尔，J.M.（1982年）《生物化学杂志》257，8233 - 8237）。本报告描述了协同eIF-2α的纯化及特性。协同eIF-2α的最高纯度制剂含有分子量分别为21,000和19,000的两种多肽。协同eIF-2α和协同eIF-2β都是热稳定因子，在有或没有Mg2+存在的情况下都能刺激三元复合物的形成，并能克服金精三羧酸的抑制作用。协同eIF-2α与协同eIF-2β的不同之处在于，协同eIF-2β能刺激eIF-2与GDP形成二元复合物，而协同eIF-2α则不能。此外，协同eIF-2α和协同eIF-2β对三元复合物形成的刺激作用接近相加，这强烈表明这两种因子独立发挥作用。协同eIF-2α和协同eIF-2β都不会提高与eIF-2结合的GDP与游离GDP之间的交换速率，这表明这两种因子都不具有鸟嘌呤核苷酸交换因子的功能。
