The subunit structure of alpha-crystallin. Isolation and characterization of the S-carboxymethylated acidic subunits from adult and embryonic origin

The present results, together with physicochemical evidence presented elsewhere, indicate that α‐crystallin from calf lens is composed of two acidic and two basic polypeptide chains. The acidic polypeptides could be isolated by chromatography on SE‐Sephadex at pH 5.5 in the presence of 7 M urea. It could be demonstrated that both S ‐carboxymethylated acidic polypeptides are of equal molecular weight and amino acid composition. In both chains N ‐acetylmethionyl‐aspartate was found as the N‐terminal and serine as the C‐terminal residue. Peptide mapping reveals one unique peptide region for each polypeptide. In embryonic α‐crystallin only one acidic polypeptide can be detected. From comparative amino acid analysis, peptide maps as well as physicochemical behaviour it may be deduced that the polypeptide present in the early embryonic stages is identical with the adult acidic polypeptide A‐2.