title: Purification and characterization of two human erythrocyte arylamidases preferentially hydrolysing N-terminal arginine or lysine residues.
abstract: Two arylamidases (I and II) were purified from human erythrocytes by a procedure that comprised removal of haemoglobin from disrupted cells with CM-Sephadex D-50, followed by treatment of the haemoglobin-free preparation subsequently with DEAE-cellulose, gel-permeation chromatography on Sephadex G-200, gradient solubilization on Celite, isoelectric focusing in a pH gradient from 4 to 6, gel-permeation chromatography on Sephadex G-100 (superfine), and finally affinity chromatography on Sepharose 4B covalently coupled to L-arginine. In preparative-scale purifications, enzymes I and II were separated at the second gel-permeation chromatography. Enzyme II was obtained as a homogeneous protein, as shown by several criteria. Enzyme I hydrolysed, with decreasing rates, the L-amino acid 2-naphtylamides of lysine, arginine, alanine, methionine, phenylalanine and leucine, and the reactions were slightly inhibited by 0.2 M-NaCl. Enzyme II hydrolysed most rapidly the corresponding derivatives of arginine, leucine, valine, methionine, proline and alanine, in that order, and the hydrolyses were strongly dependent on Cl-. The hydrolysis of these substrates proceeded rapidly at physiological Cl- concentration (0.15 M). The molecular weights (by gel filtration) of enzymes I and II were 85 000 and 52 500 respectively. The pH optimum was approx. 7.2 for both enzymes. The isoelectric point of enzyme II was approx. 4.8. Enzyme I was activated by Co2+, which did not affect enzyme II to any noticeable extent. The kinetics of reactions catalysed by enzyme I were characterized by strong substrate inhibition, but enzyme II was not inhibited by high substrate concentrations. The Cl- activated enzyme II also showed endopeptidase activity in hydrolysing bradykinin.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000626:Aminopeptidases / Q000097:blood* / Q000302:isolation & purification; D001120:Arginine; D055598:Chemical Phenomena; D002621:Chemistry; D002712:Chlorides; D002847:Chromatography, Agarose; D002848:Chromatography, DEAE-Cellulose; D002853:Chromatography, Liquid; D004912:Erythrocytes / Q000201:enzymology*; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D008239:Lysine; D013379:Substrate Specificity
chemical_list: D000596:Amino Acids; D002712:Chlorides; D001120:Arginine; D000626:Aminopeptidases; D008239:Lysine