Studies on lens proteins. III. Variations in polypeptides of lens beta-crystallins

Relative amounts of two water-soluble beta-crystallin polypeptides with molecular weights of 26,000 (26K) and 28,000 daltons (28K) were measured in a number of species and also in different age groups of rats. The data indicate an age-dependent increase in the quantity of the 26K which is concomitant with a decrease in the 28K polypeptide. The ratio of these two polypeptides in the total water-soluble fraction is similar to that observed in the purified beta-crystallins. Purified beta 3-crystallin of the rabbit and its equivalent "beta L" of the bovine lens display charge heterogeneity upon DEAE chromatography, suggesting subtle qualitative changes in these crystallins. The presence of these two polypeptides in the urea-soluble fraction of lens preparations is also an indication of qualitative changes. The 26K polypeptide of beta-crystallins studied here is different from the 26K main intrinsic membrane protein in that, unlike the latter, it does not aggregate upon heating in SDS-buffer.