Human β-crystallin: I. Comparative studies on the β₁, β₂ and β₃-crystallins

Three classes of β-crystallin, which have previously been named β₁, β₂ and β₃-crystallins, have been isolated from normal human lenses by gel filtration on Sephadex G-200. They have been compared to each other in terms of physico-chemical, immunochemical and conformational parameters. All three β-crystallins have similar secondary and tertiary structures as seen by ultraviolet circular dichroism. They appear to be very closely related immunochemically. All three are quite heterogeneous but have similar isoelectric point ranges which are more acidic than that of bovine β-crystallin. β₁, β₂ and β₃ appear to be composed in large part of identical subunits, but there are differences in the distributions of several minor polypeptides as visualized by electrophoresis in the presence of sodium dodecyl sulfate. The major distinction among the three β-crystallin classes is in molecular weight. All three classes contain a minor polypeptide or group of polypeptides of approximately 43 000 daltons which have not been seen in the β-crystallin from other species. The 43 000 dalton polypeptides were isolated from each β-crystallin class. Preliminary analysis of these preparations by isoelectric focusing and immunodiffusion was done.