Correlated changes in delta-crystallin synthesis and ion concentrations in the embryonic chick lens: summary, current experiments and speculations.

Abstract

Summaryand ImplicationsWe have described a correlation between the ratio of synthesis of the higher to the lower molecular weight polypeptides of δ‐crystallin and the intracellular concentrations of Na+ and K+ in the cultured embryonic chick lens. The only structural differences we have found between the larger and smaller δ‐crystallin polypeptides are two, acidic, methionine‐containing tryptic peptides which are absent from the lower molecular weight polypeptides. We do not yet know whether the alteration in the ratio of synthesis of the polypeptides is regulated at the post‐transcriptional or post‐translational level. We are continuing to investigate this problem by studies on the cell‐free synthesis of δ‐crystallin and by analysis of the sequences and organization of δ‐crystallin DNA.One implication of these experiments concerns protein synthesis in cataractous lenses, as has been reviewed elsewhere.15 Numerous cataracts are associated with appreciable changes in ion concentrations, particularly with an increase in Na+ and a decrease in K+. Differential reduction in crystallin synthesis has now been correlated with an increase in the Na+/K+ ratio in three types of cataracts, namely, in hereditary cataracts in mice (Nakano mouse),29 in galactose cataracts in rats,30 and in drug‐induced experimental cataracts in rats.31 It seem reasonable to propose that changes in ion concentrations will be correlated with alterations in protein synthesis in other cataracts and. possibly, with other diseases which result in electrolyte imbalances within cells.