Transglutaminase activity in normal human lenses and in senile cataracts

Transglutaminase, the main function of which is to crosslink peptide chains through isopeptide bonds, has been detected in the lens of laboratory animals and in human cataracts and has been implicated in cataractogenesis. The transglutaminase activity has been estimated by measuring the amount of 3H-putrescine incorporation into dimethyl-casein of clear noncataractous human lenses and by comparing it with that of cataracts of different grades. Both the total and specific transglutaminase activity of highly cataractous lenses were less than those of normal lenses. During the progression of cataract (slightly moderately, and highly cataractous groups were compared), there was a substantial decrease in transglutaminase activity. In contrast to our findings, an increased transglutaminase activity has been reported in the lens of rats and mice with cataract mutation. This discrepancy is probably due to the different mechanisms involved in the development of human senile cataract and cataract in mutated laboratory animals.