title: Effect of calcium ions on enteropeptidase catalysis.
abstract: The effects of calcium ions on hydrolysis of low molecular weight substrates catalyzed by different forms of enteropeptidase were studied. A method for determining activity of truncated enteropeptidase preparations lacking a secondary trypsinogen binding site and displaying low activity towards trypsinogen was developed using N-alpha-benzyloxycarbonyl-L-lysine thiobenzyl ester (Z-Lys-S-Bzl). The kinetic constants for hydrolysis of this substrate at pH 8.0 and 25 degrees C were determined for natural enteropeptidase (K(m) 59.6 microM, k(cat) 6660 min(-1), k(cat)/K(m) 111 microM(-1) x min(-1)), as well as for enteropeptidase preparation with deleted 118-783 fragment of the heavy chain (K(m) 176.9 microM, k(cat) 6694 min(-1), k(cat)/K(m) 37.84 microM(-1) x min(-1)) and trypsin (K(m) 56.0 microM, k(cat) 8280 min(-1), k(cat)/K(m) 147.86 microM(-1) x min(-1)). It was shown that the enzymes with trypsin-like primary active site display similar hydrolysis efficiency towards Z-Lys-S-Bzl. Calcium ions cause 3-fold activation of hydrolysis of the substrates of general type GD(4)K-X by the natural full-length enteropeptidase. In contrast, the hydrolysis of substrates with one or two Asp/Glu residues at P2-P3 positions is slightly inhibited by Ca2+. In the case of enteropeptidase light chain as well as the enzyme containing the truncated heavy chain (466-800 fragment), the activating effect of calcium ions was not detected for all the studied substrates. The results of hydrolysis experiments with synthetic enteropeptidase substrates GD(4)K-F(NO(2))G, G(5)DK-F(NO(2))G (where F(NO(2)) is p-nitrophenyl-L-phenylalanine residue), and GD(4)K-Nfa (where Nfa is beta-naphthylamide) demonstrate the possibility of regulation of undesired side hydrolysis using natural full-length enteropeptidase for processing chimeric proteins by means of calcium ions.
authors.affiliation: Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, 117997, Russia. anna@enzyme.siobc.ras.ru
authors.forename: A G
authors.initials: AG
authors.lastname: Mikhailova
authors.forename: V V
authors.initials: VV
authors.lastname: Likhareva
authors.forename: I A
authors.initials: IA
authors.lastname: Prudchenko
authors.forename: L D
authors.initials: LD
authors.lastname: Rumsh
mesh_terms: D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology*; D002384:Catalysis / Q000187:drug effects; D002412:Cations; D002417:Cattle; D004765:Enteropeptidase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014357:Trypsin / Q000378:metabolism; D014362:Trypsinogen / Q000378:metabolism
chemical_list: D002412:Cations; D011993:Recombinant Fusion Proteins; D014362:Trypsinogen; D014357:Trypsin; D004765:Enteropeptidase; D002118:Calcium