In situ measurements of ribulose-1,5-bisphosphate carboxylase activity by nuclear magnetic resonance

Abstract

High-resolution NMR spectroscopy is demonstrated to be capable of monitoring in situ the carboxylation reaction catalyzed by ribulose-1,5-bisphosphate carboxylase. Specific activities are determined for three enzymes from different sources containing higher plant and photosynthetic bacteria, and they are in agreement with those measured by other methods. Several important features of the reaction have been confirmed at the atomic level. A decrease in activity with time after the reaction started has also been observed for both enzymes with L8S8 and L2 structures from photosynthetic bacteria and higher plants, suggesting that the "fallover" of activity may be a more general phenomenon. 1H spectra obtained with H2O as solvent provide the most efficient quantitative measurement of the reaction product, 3-phosphoglycerate. 31P spectra give essentially the same result as 1H NMR but have the advantage of showing the degree of reaction at any time during the reaction. The incorporated carbon atom is unequivocally identified as the C-1 carbon of 3-phosphoglycerate from the 13C spectrum.