Transglutaminase activity in normal and hereditary cataractous rat lens and its partial purification

Hereditary cataractous rat lenses showed significantly higher specific activity for transglut minase than the normal lenses of comparable age. Transglutaminase activity of normal lenses was distributed predominantly in the buffer-soluble fraction. The buffer-insoluble fraction showed 14% of total activity. The cortical and nuclear fractions of the normal lens showed 43% and 57% distribution of total activity, respectively. Protein solubilizing agents enhanced the activity of the enzyme in the lens homogenate in the following order: Triton X-100 > Tween 20 > Sodium dodecyl sulfate > Sodium deoxycholate > Sodium cholate > NaSCN > KI. Transglutaminase was purified 15 fold by hydrophobic affinity chromatography employing omega-amine octylagarose matrix. The purified enzyme was activated by calcium and inactivated by iodoacet-amide and upon freeze-drying. Lens crystallins served as exogenous substrate for transglutaminase, with y-crystallin as the most effective amine acceptor.