HUMAN ALPHA-CRYSTALLIN .1. ISOLATION AND CHARACTERIZATION OF NEWLY SYNTHESIZED ALPHA-CRYSTALLIN

Abstract

Studies of the incorporation of 14C amino acids into human lens proteins demonstrated that an .alpha.-crystallin fraction took up more than 6 times as much radioactivity as any other lens protein. Based on analyses with a calibrated Bio-Gel A-1.5 m column, a MW of 4.9 .times. 105 .+-. 5% was obtained for this protein, while sedimentation equilibrium analyses indicated a weight average MW of 7.5 .times. 105 .+-. at 10,000 rpm. Gel electrophoresis in sodium dodecyl sulfate revealed 2 components with MW of 22,000 and 20,000, values similar to calf .alpha.-crystallin. Alkaline urea gel electrophoresis indicated 1 major polypeptide with a mobility similar to the B2 chain of calf .alpha.-crystallin and 2 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 was very similar to that of calf .alpha.-crystallin. All 3 major polypeptides contained 14C amino acids. From the present data it was not determined whether the 3 polypeptides were independently synthesized or a rapid transformation produced one of the labeled polypeptides in the A region. There appears to be between 3-4 times as many presumptive A as B polypeptides.