A CYSTEINE PROTEINASE-INHIBITOR IN CRAB RETINA CRYSTALLINE CONES - PURIFICATION AND IMMUNOHISTOCHEMICAL LOCALIZATION

The labile cytoskeleton of arthropod rhabdomeral microvilli can be sta bilised for electron microscopy by pretreatments with cysteine protein ase inhibitors, implying that retinas contain cysteine proteinases and regulatory cystatins or calpastatins. A 50 kDa cysteine proteinase in hibitor was isolated from retinas of a crab, Leptograpsus. Its functio n as an active cysteine proteinase inhibitor was established by a papa in caseinolysis assay. Monoclonal antibodies raised against a 13 kDa r ecombinant Drosophila cystatin recognised a crab 50 kDa kininogen-like glycoprotein, Indicating that it is the inhibitor. Although approxima tely 40 mu g of the crab protein was present in a crab retina, immunol ocalisation suggested that it may be largely confined to the crystalli ne cones. The role of this 50 kDa inhibitor in the crystalline cones i s presently unknown. The proteins responsible for stabilising arthropo d rhabdomeral cytoskeletons have yet to be elucidated.