Interactions of lens proteins. Self-association and mixed-association studies of bovine alpha-crystallin and gamma-crystallin.

Concentrated solutions of calf alpha-crystallin (up to 45 g/l) and gamma-crystallin (up to 67 g/l) were subjected to frontal exclusion chromatography at pH 7.3, ionic strength 0.17 and 20 degrees C. The experimental concentration dependence of the weight-average partition coefficient was compared with theoretical expressions, which include considerations of thermodynamic non-ideality effects, for the concentration dependence of a single solute and of a solute undergoing reversible self-association. Two types of association pattern were examined, discrete dimerization and indefinite self-association. The partition chromatography results are consistent with an indefinite self-association of gamma-crystallin, governed by an isodesmic association constant of 6.7 X 10(-3) l/g. alpha-Crystallin appears to self-associate either very weakly, with a maximal association constant of 0.9 X 10(-3) l/g, or not at all; the distinction depends on the assessment of the non-ideality coefficients. The consequences of excluded volume effects on these self-association equilibria at high total protein concentration are discussed. Mixtures of alpha-crystallin and gamma-crystallin were analyzed by frontal exclusion chromatography (up to 14 g/l) and sedimentation velocity (up to 115 g/l): no interaction was observed.