P-31-NMR STUDIES OF NADPH, NADP(+) AND THE COMPLEX OF NADPH AND METHOTREXATE WITH LACTOBACILLUS-CASEI DIHYDROFOLATE-REDUCTASE IN THE SOLID-STATE

P-31-NMR spectra on solid samples of NADP(+), NADPH and NADPH bound to Lactobacillus casei dihydrofolate reductase have been recorded using the techniques of cross polarisation, magic angle spinning and high power proton decoupling. The isotropic chemical shifts, the principal components of the shielding tensors and the asymmetry parameters for the P-31 nuclei in the 2'-phosphate and pyrophosphate groups have been measured. The isotropic shifts show similar trends to the chemical shifts measured in solution. The isotropic shifts and the shielding tensors for the dianionic and monoanionic states of the 2'-phosphate group have been determined and the presence of both ionisation states has been detected in a solid sample of the lyophilised complex of L. casei dihydrofolate reductase with NADPH and methotrexate. This contrasts with the behaviour in solution, where only the dianionic form is bound to the enzyme. The signals from the two pyrophosphates P-31 nuclei in bound NADPH were resolved and identified. The asymmetry parameters in the different ionisation states and the orientations of the shielding tensors within the molecular framework are considered in the context of previous P-31 studies on phosphate-containing compounds.