The pyridoxal-5′-phosphate-dependent catalytic antibody 15A9: its efficiency and stereospecificity in catalysing the exchange of the α-protons of glycine

Abstract13C-NMR has been used to follow the exchange of the α-protons of [2-13C]glycine in the presence of pyridoxal-5′-phosphate and the catalytic antibody 15A9. In the presence of antibody 15A9 the 1st order exchange rates for the rapidly exchanged proton of [2-13C]glycine were only 25 and 150 times slower than those observed with tryptophan synthase (EC 4.2.1.20) and serine hydroxymethyltransferase (EC 2.1.2.1). The catalytic antibody increases the 1st order exchange rates of the α-protons of [2-13C]glycine by at least three orders of magnitude. We propose that this increase is largely due to an entropic mechanism which results from binding the glycine-pyridoxal-5′-phosphate Schiff base. The 1st and 2nd order exchange rates of the pro-2S proton have been 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 glycine the antibody preferentially catalyses the exchange of the pro-2S proton of glycine. The stereospecificity of the 2nd order exchange reaction was quantified and we discuss mechanisms which could account for the observed stereospecificity