Age-Dependent Changes in the Structure of Alpha Crystallin

Abstract

Studies upon alpha crystallin have indicated that it is composed of at least three distinct sized populations of macromolecules. Investigation of the relative amounts of these populations in bovine lenses has shown that with increasing age the proportion of the largest-sized population with molecular weights above 1 x 10⁷ increases more than fivefold. This dramatic change in the relative proportion of the high molecular weight fraction occurred only in alpha crystallin isolated from the inner 30 per cent of the lens. No difference in amino acid composition or subunit size was observed between the three populations. However, the high molecular weight species was shown to contain approximately three per cent hexose, while the low molecular weight species had only trace amounts of hexose. This sugar was shown to be glucose. Reaggregation of the deaggregated high molecular weight protein in the absence of glucose resulted in transformation to the low molecular weight population, but in the presence of glucose the original population of macromolecules appeared to be reconstituted. Reconstitution of the deaggregated low molecular weight species in the presence of glucose only gave the high molecular weight species with alpha crystallin isolated from older lens nuclear material. In the absence of glucose the original population was again reconstituted.