Estimation of cytoplasmic free Mg2+ levels and phosphorylation potentials in mungbean root tips by in vivo 31P NMR spectroscopy

Estimation of cytoplasmic free Mg2+ levels and phosphorylation potentials in mungbean root tips by in vivo 31P NMR spectroscopy

1988

A:PS

The cytoplasmic [MgATP]/[ATP]free ratios, free Mg2+ concentrations, and phosphorylation potentials in mungbean [Vigna mungo (L.) Hepper] root tip cells were investigated by 31P nuclear magnetic resonance spectroscopy. 31P NMR spectra show well defined peaks due to G6P, cytoplasmic Pi, vacuolar Pi, ATP, UDP-glucose and nicotinamide adenine nucleotides. The concentrations of phosphorus metabolites were determined from quantitative 31P NMR spectra. The [MgATP]/[ATP]free ratio was 9.45. Accordingly, about 90% of the cytoplasmic ATP was complexed to Mg2+. Utilizing the dissociation constant (Kd) determined for MgATP, the cytoplasmic free Mg2+ concentration was estimated to be 0.4 mM. The NMR-derived phosphorylation potential, [ATP]/([ADP][Pi], was 960 M-1. The sodium azide treatment decreased the [ATP]/[ADP] ratio and the phosphorylation potential, and increased the [Mg2+]free. Metabolic inhibition may have been enhanced by an increase in [Mg2+]free and a decrease in the free energy change for ATP hydrolysis, which resulted due to a decrease in the ATP level. [AS]

v.29(6):919-924, PLANT AND CELL PHYSIOLOGY

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