title: Identification of a kallikrein-like latent serine protease in human erythrocyte membranes.
abstract: We have discovered and characterized a kallikrein-like latent serine protease in intact human erythrocytes and ghosts. The enzyme is activatable by trypsin. The solubilized enzyme has esterolytic activity with a pH optimum of 9; but the membrane-associated activity increases almost linearly up to pH 10. The activated enzyme releases kinin from bovine low molecular weight kininogen. Enzyme activity is inhibited by TosLysCH2Cl , phenylmethylsulfonyl fluoride, aprotinin and amiloride, and weakly by soybean or lima bean trypsin inhibitor. It is inhibited by Co2+, Zn2+ and Mn2+ but is stimulated by Fe2+, deoxycholate and phospholipase A2. An erythrocyte membrane protein (Mr = 88,000) with an active site serine residue was identified with [14C]-diisopropylphosphorofluoridate labeling. Consistent with the finding of tryptic activation of the latent erythrocyte serine protease, trypsin treatment reduced the density of labeling of this protein and revealed a lower molecular weight form (Mr = 64,000). Possible relationships between the activity of this newly identified serine protease and events such as erythrocyte membrane ion fluxes might be of interest.
mesh_terms: D001665:Binding Sites; D010450:Endopeptidases / Q000097:blood*; D004789:Enzyme Activation / Q000187:drug effects; D004910:Erythrocyte Membrane / Q000201:enzymology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007610:Kallikreins / Q000097:blood*; D010447:Peptide Hydrolases / Q000097:blood; D012697:Serine Endopeptidases; D014357:Trypsin / Q000494:pharmacology
chemical_list: D010450:Endopeptidases; D010447:Peptide Hydrolases; C023073:tosylarginine methyl ester hydrolase; D007610:Kallikreins; D012697:Serine Endopeptidases; D014357:Trypsin