Lens transglutaminase and cataract formation.
A protein polymer characteristically present in human cataract was shown to contain significant amounts of gamma-glutamyl-epsilon-lysine isopeptides. It is proposed that these crosslinks are produced by the action of transglutaminase (R-glutaminyl-peptide:amine-gamma-glutamyl-yltransferase, EC 2.3.2.13), which is all the more plausible because lens contains the enzyme and endogenous protein substrates for it. The enzyme is similar to that obtained from liver and is Ca2+ dependent. Highest apparent activity is found in lens cortex. When cortex homogenate from the rabbit was incubated in the presence of Ca2+ with either [14C]putrescine or with dansylcadaverine, a a selective incorporation of the radioactive or fluorescent amine into the heavier subunits (Mr approximately 26,000 and 30,000) of beta-crystallins could be demonstrated. Possible modes of regulating the crosslinking activity of this enzyme in lens are discussed.
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002386:Cataract / Q000201:enzymology / Q000209:etiology*; D002417:Cattle; D003459:Crystallins / Q000032:analysis; D006168:Guinea Pigs; D006801:Humans; D007700:Kinetics; D007908:Lens, Crystalline / Q000201:enzymology*; D046911:Macromolecular Substances; D008970:Molecular Weight; D011700:Putrescine / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D013045:Species Specificity; D005723:gamma-Glutamyltransferase / Q000378:metabolism*
D003459:Crystallins; D046911:Macromolecular Substances; D005723:gamma-Glutamyltransferase; D002118:Calcium; D011700:Putrescine