Studies on Lens Protein Polypeptides

¹ Department of Ophthalmology, New York University School of Medicine, New York, N.Y. 10016

Methods for the separation and identification of the polypeptide chains of each lens crystallin are basic to the study of these proteins on polyribosomes. Rabbit lens proteins have been deaggregated, denatured, and reduced to polypeptide chains, and separated by polyacrylamide gel electrophoresis. Approximate molecular weights of the resultant chains have been calculated by the same system. Vigorous denaturation and reduction with sodium dodecyl sulfate and 2-mercaptoethanol disrupts all structure other than primary structure, degrading each protein to its component polypeptides. The separation method employed is almost exclusively dependent on molecular size. Deaggregated alpha crystallin is a group of chains, each of about 20,000 molecular weight. The beta crystallin region of the DEAE chromatogram yields three polypeptides of estimated molecular weights 21,000, 23,000, and 29,000. Preliminary studies on the four beta crystallin peaks isolated by DEAE-chromatography suggest that one or more may be composed of aggregates of different polypeptide chains. Gamma crystallins appear to be single polypeptide chain proteins of molecular weights from 18,000 to 21,000. Experiments performed on lens epithelium indicate that a significant percentage of their newly synthesized proteins are nuclear and cytoplasmic proteins other than the crystallins.