Subunit Composition of Rabbit Lens Beta Crystallins

¹ Department of Ophthalmology, New York University Medical Center, New York, N.Y.

DEAE-purified rabbit beta crystallins have been studied by sedimentation on sucrose gradients and their subunits characterized by co-electrophoresis in SDS-polyacrylamide gels. The experiments indicate that the beta crystallins isolated by DEAE-cellulose are a large family of related proteins with sedimentation velocities of about 4S. Deaggregation and denaturation of these proteins to polypeptides and subsequent electrophoretic analysis yields three groups of subunits with calculated, molecular weights of 21,000, 23,000, and 29,000. The minimum total number of polypeptide chains in the three groups is five. Each of the beta crystallins is made up of two or three such chains. Aggregation and loss of solubility occur readily during concentration procedures. In the course of these experiments, it became evident that alpha crystallin is composed of at least two different sizes of polypeptide chains.