Localization and characteristics of transglutaminase in the rabbit and human eye

Transglutaminases (transamidases; endo-gamma-glutamine: zeta-lysine transferases) are calcium-dependent enzymes, which cross-link proteins by introducing covalent zeta-(gamma-glutaminyl)lysine pseudopeptide bonds between the molecules. The distribution and characteristics of transglutaminase in both human and rabbit eyes have been studied. Transglutaminase activity was measured with an isotope technique based on the enzyme catalysed incorporation of 14C-putrescine into casein. Electrophoretic characteristics were studied using agarose gel electrophoresis combined with a specific fluorescent activity staining procedure based on the transglutaminase catalysed incorporation of monodansylthiacadaverine into casein. A thrombin-independent enzyme, indistinguishable from the guinea pig liver transglutaminase with regard toi electrophoretic mobility, was found in the choroid/pigment epithelium and ciliary body of the human eye while the lens, retina, iris and vitreous humour did not contain detectable amounts. The lens and the choroid/pigment epithelium of the rabbit eye tissues contained high activities while the activity in the extract from the combined ciliary body/iris was low but measurable.