Heterogeneity in the beta-subunit of translational initiation factor eIF-2 during brain development.

We have detected by immunoblotting analysis of crude fractions from suckling and adult rat brain, resolved by two-dimensional isoelectric focusing-dodecyl sulfate polyacrylamide gel electrophoresis, the presence of two different forms of the beta subunit of polypeptide initiation factor 2 (eIF-2). These two forms differ in their apparent molecular weights and also in their isoelectric point values. Quantitation of both forms in the crude fractions shows that, the most basic form beta 1 (pI: 6.1, 52 kDa), is present in higher levels of the salt wash ribosomal fractions obtained from both, suckling and adult animals, than in the postmicrosomal fraction corresponding to the same animals. The most acidic form, beta 2 (pI: 5.9, 50 kDa), is present in the highest level in the postmicrosomal supernatant from adult animals. A close parallelism is found between beta 1 levels and eIF-2 activity.