Role of O-linked carbohydrate of human urinary trypsin inhibitor on its lysosomal membrane-stabilizing property

Human urinary trypsin inhibitor (UTI) was digested with various enzymes to obtain O-glycoside linked N-terminal glycopeptide (UTIm1), N-glycoside linked C-terminal tandem Kunitz-domains (domain I and II, UTIm2), UTI lacking O-glycoside (UTIc), asialo UTI (UTIa) and UTI lacking N-glycoside (UTIn). We investigated the membrane stabilizing effect of these UTI derivatives on rat renal lysosome by measurement of lysosomal enzyme N-acetyl-beta-D-glucosaminidase (NAG) release after hypotonic treatment. Intact UTI suppressed NAG release, but aprotinin, gabexate mesilate (FOY), nafamostat mesilate (FUT) and recombinant domain II of UTI (R-020) had no effect, indicating that inhibition of serine proteases was not involved and the carbohydrate moiety of UTI might be necessary for this property. Among UTI derivatives, UTIm1, UTIm2, UTIm1+ UTIm2, and UTIc had no effect. In contrast, UTIa or UTIn suppressed NAG release. From these results, we conclude that O-glycoside linked core protein without N-glycoside is essential to the lysosomal membrane-stabilizing property of UTI. (C) 1998 Academic Press.