title: Stereospecificity of alpha-proton exchange reactions catalysed by pyridoxal-5'-phosphate-dependent enzymes.
abstract: A NMR method for quantifying the catalytic efficiency and stereospecificity of the exchange of the alpha-protons of glycine is described. It is used to determine how the binding of the alpha-carboxylate group of amino acids contributes to the stereospecificity of exchange reactions catalysed by tryptophan synthase, serine hydroxymethyltransferase and a catalytic antibody utilising pyridoxal-5'-phosphate (PLP) as a cofactor. Using larger substrates, it is shown how the size of the amino acid side chain contributes to the stereospecificity of exchange. Mutants of aspartate aminotransferase are used to determine how substrate binding controls the catalytic efficiency and stereospecificity of the exchange of the alpha-protons of aspartate and glutamate. Evidence is presented which shows that with serine hydroxymethyltransferase, L-norleucine is not bound at the same catalytic site as glycine. Finally the catalytic efficiency and stereospecificity of the alpha-proton exchange reactions catalysed by all the PLP-dependent catalysts examined are compared.
authors.affiliation: Department of Biochemistry and Centre for Synthesis and Chemical Biology, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Merville House Belfield, Dublin 4, Ireland. J.Paul.G.Malthouse@ucd.ie
authors.forename: J Paul G
authors.initials: JP
authors.lastname: Malthouse
mesh_terms: D000626:Aminopeptidases / Q000737:chemistry; D002384:Catalysis; D020134:Catalytic Domain; D043384:Glutamyl Aminopeptidase; D012696:Glycine Hydroxymethyltransferase / Q000737:chemistry* / Q000378:metabolism; D008968:Molecular Conformation; D019906:Nuclear Magnetic Resonance, Biomolecular; D011732:Pyridoxal Phosphate / Q000737:chemistry* / Q000378:metabolism; D014367:Tryptophan Synthase / Q000737:chemistry* / Q000378:metabolism
chemical_list: D011732:Pyridoxal Phosphate; D012696:Glycine Hydroxymethyltransferase; D000626:Aminopeptidases; D043384:Glutamyl Aminopeptidase; D014367:Tryptophan Synthase