Biochemistry of bovine lens proteins I. Isolation and characterization of adult α-crystallins

By the use of DEAE-cellulose fractionation it has been shown that the cortical fibers of the adult bovine lens contain several proteins not found in the nuclear lens fibers. Electrophoresis of the protein peaks obtained from the cellulose column revealed the heterogeneity of the α-, β-, and γ-crystallins. The α-crystallins were extensively purified by isoelectric precipitation and fractionation on DEAE-cellulose. Using these procedures, 4 α-crystallins have been isolated. Further evidence for the presence of 4 α-crystallins in the cortical lens fibers was obtained by immunochemical analysis of the isoelectric precipitated α-crystallin. Physicochemical data on these α-crystallins are also presented. In addition to this it has been shown that two of the α-crystallins undergo transformation under alkaline pH. This transformation results in the formation of a molecule which is half the size of the normal α-crystallin. The transformation is not reversible, and a mixture of the normal and transformed proteins can only be resolved by ultracentrifugation. This mixture cannot be resolved by electrophoresis at alkaline pH.