Purification of the Elongation Factors Present in Spinach Chloroplasts

Elongation factor G (EF-Gchl) and elongation factor Tu (EF-TUchl) have been purified from isolated spinach chloroplasts. On polyacrylamide gel electrophoresis the purifed proteins appear to be at least 70% pure. The molecular weight has been estimated to be 77000 and 45500 for EF-Gchl and EF-TUchl respectively. Chloroplast elongation factor T (EF-Tchl) has been only partially purified. Gel electrophoresis under non-denaturing and denaturing conditons indicate that EF-T-chl is most probably composed of two polypeptides, one of which has an electrophoretic mobility identical to that of EF-TUchl. EF-TUchl appears to represent approximately 7% of the chloroplast soluble protein while EF-Gchl accounts for less than 1%. Just as in the case of the bacterial factors, EF-TUchl appears to be in excess as compared to EF-Gchl. Although no data were obtained on the concentration of EF-Tchl, it may be assumed that the three elongation factors represent approximately 10% of the chloroplast soluble protein.