Human alpha-crystallin. I. The isolation and characterization of newly synthesized alpha-crystallin

Studies of the incorporation of 14C amino acids into human lens proteins demonstrate that an alpha-crystallin fraction takes up more than six times as much radioactivity as any other lens protein. Based on analyses with a calibrated Bio-Gel A-1.5 m column, a molecular weight of 4.9 x 10(5) +/- 5 per cent was obtained for this protein while sedimentation equilibrium analyses indicated a weight average molecular weight, Mw, of 7.5 x 10(5) +/- 4 per cent at 10,000 r.p.m. Gel electrophoresis in sodium dodecyl sulfate revealed two components with molecular weights of 22,000 and 20,000, values similar to those found with calf alpha-crystallin. Alkaline urea gel electrophoresis indicated one major polypeptide with a mobility similar to the B2 chain of calf alpha-crystallin and two major bands with mobilities between those of the calf alpha-crystallin A2 and A1 chains. Amino acid analyses of this newly synthesized alpha-crystallin gave a composition which with a few exceptions is very similar to that of calf alpha-crystallin. All three major polypeptides contained 14C amino acids. However, from the present data, it cannot be determined whether the three polypeptides were independently synthesized or a rapid transformation produced one of the labeled polypeptides in the A region. There appears to be between three and four times as many presumptive A as B polypeptides.