Purified eukaryotic initiation factor 2 from calf liver consists of two polypeptide chains of 48,000 and 38,000 daltons.

Eukaryotic initiation factor 2 (eIF-2), which specifically binds Met-tRNAMetf and forms stable ternary complexes with GTP, has been purified from ribosomal salt wash proteins from calf liver. The purified factor exhibits only two polypeptide bands of Mr = 48,000 and 38,000 following electrophoresis in 15% polyacrylamide gels in the presence of sodium dodecyl sulfate. Densitometric tracings show the two polypeptides are present in a molar ratio of 1:1. This suggests a Mr = 86,000 for the native enzyme, a value which agrees with the apparent molecular weight determined by physical methods. Less pure preparations of eIF-2 show additional polypeptide bands, including 50,000- and 46,000-dalton bands, all of which can be removed by further purification without affecting the activity of eIF-2.