Lens transglutaminase and cataract formation.

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Abstract
A protein polymer characteristically present in human cataract contained significant amounts of .gamma.-glutamyl-.epsilon.-lysine isopeptides. These crosslinks may be produced by the action of transglutaminase (R-glutaminyl-peptide:amine-.gamma.-glutamyl-yltransferase, EC 2.3.2.13); 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 selective incorporation of the radioactive or fluorescent amine into the heavier subunits (MW .apprxeq. 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.