Characterization of lens proteins. II. γ-Crystallin of normal and cataractous rat lenses

Abstract

The γ-crystallin isolated from soluble normal rat lens cortex protein was fractionated into six subfractions (a-f), on SP-Sephadex C-25. Subfraction a, the first peak eluted, constituted 11% and subfractions (b-f) 33, 25, 13, 12 and 6%, respectively of the total protein. The amino acid compositions of the subfractions of the normal rat lens were determined. Arginine, glutamic acid, aspartic acid and tyrosine were the most abundant amino acids followed by glycine, serine and leucine. These data are similar to those previously reported on the subfractions of calf lens γ-crystallin. Glycine was found to be the only N-terminal amino acid in the rat γ-crystallin. The 5+ galactose-induced cataractous rat lens contained less than 10% of the γ-crystallin of the normal rat lens. Six corresponding subfractions were obtained from the γ-crystallin of the cataractous rat lens and the distribution was 5, 27, 41, 13, 12 and 2%. Preparations of γ-crystallin of the calf lens from Sephadex G-75 ( Bjork, 1961) and from Sephadex G-200, superfine ( Ocken et al., 1977) were fractionated on the SP-Sephadex columns. The separation of both preparations was identical. However, the profiles are different in that our procedure yielded 28% subfraction a while the other yielded 5–8%. The subfractions of γ-crystallin of both the rat and calf were subjected to polyacrylamide disc gel electrophoresis. The protein components shown in the gels were confirmed by the isoelectric focusing patterns. Instability of the subfractionated rat lens γ-crystallin was observed under our experimental conditions. This appears to be due to some form of equilibrium between the major and minor proteins in the subfractions.