THE PYRIDOXAL-5'-PHOSPHATE-DEPENDENT CATALYTIC ANTIBODY 15A9 - ITS EFFICIENCY AND STEREOSPECIFICITY IN CATALYZING THE EXCHANGE OF THE ALPHA-PROTONS OF GLYCINE

C-13-NMR has been used to follow the exchange of the alpha-protons of [2-C-13]glycine in the presence of pyridoxal-5'-phosphate and the cata lytic antibody 15A9, In the presence of antibody 15A9 the 1st order ex change rates for the rapidly exchanged proton of [2-C-13]glycine were only 25 and 150 times slower than those observed with tryptophan synth ase (EC 4.2.1.20) and serine hydroxymethyltransferase (EC 2.1.2.1). Th e catalytic antibody increases the Ist order exchange rates of the alp ha-protons of [2-C-13]glycine by at least three orders of magnitude. W e propose that this increase is largely due to an entropic mechanism w hich results from binding the glycine-pyridoxal-5'-phosphate Schiff ba se, The 1st and 2nd order exchange rates of the pro-2S proton have bee n determined but we were only able to determine the 2nd order exchange rate for the pro-2R proton of glycine, In the presence of 50 mM glyci ne the antibody preferentially catalyses the exchange of the pro-2S pr oton of glycine, The stereospecificity of the 2nd order exchange react ion was quantified and we discuss mechanisms which could account for t he observed stereospecificity, (C) 1998 Federation of European Biochem ical Societies.