31P NMR spin‐transfer in the phosphoglyceromutase reaction

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Abstract
The rate of exchange of phosphoryl groups between 2- and 3-phosphoglycerate catalyzed by high concentrations (.apprxeq. 5.0 mg protein ml-1) of rabbit muscle phosphoglyceromutase and lysed human erythrocyte was measured using saturation and inversion transfer techniques with 31P-NMR spectroscopy. This is the 1st reported application of these techniques to a study of this particular enzymic reaction either in vitro or in situ in a cell cytosol. Selective irradiation of resonances was achieved by the DANTE pulse sequence which had not previously been used for spin-transfer studies. New equilibrium exchange theory was developed for the simplest model of a 2-reactant enzyme-catalyzed reaction and this was used to calculate turnover rates for the enzymes. There was a close similarity between the turnover rates calculated from the spin-transfer data obtained from the systems in vitro and in situ, and those obtained by conventional enzymic assays at low enzyme concentrations. This suggested an absence of any homogeneous enzyme-enzyme interactions which modify the kinetics at high protein concentrations either in lysates or in the system in vitro.

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