THE STRUCTURE OF THE ACIDIC POLYPEPTIDE CHAINS FROM α-CRYSTALLIN. AMINO ACID COMPOSITION, PEPTIDE MAPPING, AND N-TERMINUS

Carefully performed amino acid analyses of the acidic polypeptides from the bovine eye lens protein α‐crystallin were in agreement with the recently found molecular weight of about 12,000 for these chains. The proposed amino acid composition is: (Asp10, Thr3, Ser 15(14), Glu11, Pro7, Gly6, Ala4(3), Val6, Met, Ile5, Leu8, Tyr3, Phe8, Lys4, His4, Arg8, Cys, Try). On tryptic digestion both polypeptide chains yielded a rather small number of nin‐hydrin‐positive spots on peptide maps; 15 strong and 4 very light spots for A‐l and 14 strong and 4 light spots for A‐2. After blocking the ɛ‐amino groups of the lysine residues by trifluoro acetylation, the acidic chains, again, were submitted to tryptic digestion. Both chains, A‐l and A‐2, appeared to contain the same N‐terminus up to the first arginine residue. In connection with recent findings, its amino acid sequence is proposed to be: acetyl‐Met‐Asp‐Ile‐Ala‐Ile‐Gln‐His‐Pro‐Try‐Phe‐Lys‐Arg.