title: Methyltrypsin: a novel probe of proteinase-inhibitor interactions.
abstract: Incubation of trypsin with m-guanidinobenzenesulfonic acid methyl ester (mGBSOM) under mild conditions resulted in its quantitative and specific conversion to N-3-methylhistidinyl-57-trypsin (methyltrypsin). The interactions of alpha-2-plasmin inhibitor (alpha 2PI) and alpha-1-proteinase inhibitor (alpha 1PI) with the active-site modified enzymes methyltrypsin and dehydroalanyl-195-trypsin (anhydrotrypsin) were studied by thionine difference spectroscopy. For methyltrypsin the KA with alpha 1PI and alpha 2PI was 2.7 X 10(5) M-1 and 1.3 X 10(5) M-1, respectively, and with anhydrotrypsin, 7.0 X 10(3) M-1 and 3.2 X 10(5) M-1, respectively.
mesh_terms: D007611:Aprotinin / Q000378:metabolism; D001557:Benzenesulfonates / Q000494:pharmacology; D001665:Binding Sites; D001667:Binding, Competitive; D001798:Blood Proteins / Q000378:metabolism; D006146:Guanidines / Q000494:pharmacology; D006639:Histidine / Q000031:analogs & derivatives*; D008762:Methylhistidines / Q000378:metabolism*; D010640:Phenothiazines / Q000378:metabolism; D011480:Protease Inhibitors / Q000378:metabolism*; D013053:Spectrophotometry; D014357:Trypsin / Q000378:metabolism*; D000515:alpha 1-Antitrypsin; D000979:alpha-2-Antiplasmin / Q000378:metabolism
chemical_list: D001557:Benzenesulfonates; D001798:Blood Proteins; D006146:Guanidines; D008762:Methylhistidines; C053497:N-(3-methylhistidinyl)-57-trypsin; D010640:Phenothiazines; D011480:Protease Inhibitors; D000515:alpha 1-Antitrypsin; D000979:alpha-2-Antiplasmin; C011661:anhydrotrypsin; C053496:3-guanidinobenzenesulfonic acid methyl ester; D006639:Histidine; D007611:Aprotinin; D014357:Trypsin; C009469:thionine