Calcium-induced opacification of rat lens beta-crystallin solution: its susceptibility to H2O2 oxidation

Isolation of alpha, beta and gamma-crystallin solutions from rat lens soluble fraction was carried out by DEAE-cellulose ion-exchange column chromatography, and the effects of H2O2 on calcium-induced opacification of these solutions was examined. The alpha-crystallin solution became turbid in the presence of 1-10 mM calcium ions, and the turbidity increased with increasing calcium concentrations. The opacification level of the alpha-crystallin solution was not affected by 200 microM H2O2 treatment for 24 hours. On the other hand, the calcium-induced turbidity of a solution of beta-crystallin not treated with H2O2 was about one-third that of the alpha-crystallin, but by the H2O2 oxidation, its calcium-induced opacification was remarkably accelerated beyond the opacification level of the alpha-crystallin. The gamma-crystallin solution was made turbid by the H2O2 oxidation, but its turbidity was changed little by the addition of calcium ions. From the above results, it is suggested that the H2O2 acceleration of calcium-induced opacification of whole soluble lens protein solution previously reported might be mainly due to the aggregation properties of beta-crystallin. Furthermore, it is proposed that in the whole soluble lens protein, the calcium-induced aggregation of alpha-crystallin might be kept at almost the same low level whether the H2O2 treatment is done or not, and that the beta-crystallin might be more susceptible to H2O2 than the alpha- and gamma-crystallins.