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The structures of copper amine oxidases from various sources show good similarity, suggesting similar catalytic mechanisms for all members of this enzyme family. However, the optimal substrates for each member differ, depending on the source of the enzyme and its location. | ijFEBS Journal Active site residue involvement in monoamine or diamine oxidation catalysed by pea seedling amine oxidase Maria Luisa Di Paolo1 Michele Lunelli2 Monika Fuxreiter2 3 Adelio Rigo1 Istvan Simon3 and Marina Scarpa2 1 Dipartimento di Chimica Biologica and INBB Universita di Padova Padova Italy 2 Dipartimento di Fisica University di Trento Trento Italy 3 Institute of Enzymology Hungarian Academy of Sciences Budapest Hungary Keywords amine oxidase substrate docking substrate selectivity substrate-dependent catalytic mechanism titratable amino acids Correspondence M. Scarpa Dipartimento di Fisica Via Sommarive 14 38050 Povo-Trento Italy Fax 39 0461881696 Tel 39 0461882029 E-mail marina.scarpa@unitn.it Received 13 October 2010 revised 24 December 2010 accepted 2 February 2011 doi 10.1111 j.1742-4658.2011.08044.x The structures of copper amine oxidases from various sources show good similarity suggesting similar catalytic mechanisms for all members of this enzyme family. However the optimal substrates for each member differ depending on the source of the enzyme and its location. The structural factors underlying substrate selectivity still remain to be discovered. With this in view we examined the kinetic behaviour of pea seedling amine oxidase with cadaverine and hexylamine the first bearing two and the second only one positively charged amino group. The dependence of Km and catalytic constant kc values on pH ionic strength and temperature indicates that binding of the monoamine is driven by hydrophobic interactions. Instead binding of the diamine is strongly facilitated by electrostatic factors controlled by polar side-chains and two titratable residues present in the active site. The position of the docked substrate is also essential for the participation of titratable amino acid residues in the following catalytic steps. A new mechanistic model explaining the substrate-dependent kinetics of the reaction is discussed. Introduction Copper amine oxidases .
