Pressure response of P chemical shifts of adenine nucleotides.

High pressure NMR spectroscopy is a powerful method for identifying rare conformational states of proteins from the pressure response of their chemical shifts. Many proteins have bound adenine nucleotides at their active centers, in most cases in a complex with Mg-ions. The P NMR signals of phosphate groups of the nucleotides can be used as probes for conformational transitions in the proteins themselves. For distinguishing protein specific pressure effects from trivial pressure responses not due to the protein interaction, data of the pressure response of the free nucleotides must be available. Therefore, the pressure response of P chemical shifts of the adenine nucleotides AMP, ADP, and ATP and their Mg-complexes has been determined at pH values several units distant from the respective pK-values. It is clearly non-linear for most of the resonances. A negative first order pressure coefficient B was determined for all P resonances except Mg·AMP indicating an upfield shift of the resonances with pressure. The smallest and largest negative values are obtained for the α-phosphate group of ADP and β-phosphate group of Mg·ATP with -0.32 and -4.59ppm/GPa, respectively. With exception of the α-phosphate group of Mg·AMP the second order pressure coefficients are positive leading to a saturation like behaviour. The pressure response of the adenine nucleotides is similar but not identical to that observed earlier for guanine nucleotides. The obtained data show that the chemical shift pressure response of the different phosphate groups is rather different dependent on the position of phosphate group in the nucleotide and the nucleotide used.