Localization of leucine aminopeptidase in normal hog lens by immunofluorescence and activity assays

Rabbit antisera to purified bovine lens leucine aminopeptidase (EC 3.4.11.1, LAP) were prepared and shown to be specific for leucine aminopeptidase alone (Taylor et al Cur Eye Res 2:47-56, 1982). When whole hog lens thin sections were treated first with these antisera and then with fluorescein conjugated goat anti-rabbit gamma globulin, greatest fluorescence was observed in the elongating epithelium and outer cortex, and significantly less fluorescence was observed in the lens core. That largest amounts of LAP are present in the epithelium is supported by activity measurements using leucylamide as substrate. The specific activity of LAP in the epithelium/outer cortex is 83 times that of LAP in the inner cortex. The concentration of posttranslationally (postsynthetically) modified and oxidized crystallins is greatest in the core, yet in this zone there is a paucity of aminopeptidase activity, possibly due to age-related degradation of the enzyme. It is possible that LAP is in association with membranes and present in nucleoplasm of rapidly metabolizing, elongating epithelial cells. These observations are discussed in relation to the possible role of proteolysis in cataractogenesis.