31P nuclear magnetic resonance of phosphonic acid analogues of adenosine nucleotides as functions of pH and magnesium ion concentration.

The 31P NMR proton-decoupled spectra of alpha, beta-methylene-ATP [Ap(CH2)pp], beta, gamma-methylene-ATP [App(CH2)p], and alpha, beta-methylene-ADP [Ap(CH2)p] were measured as functions of pH and Mg2+ concentration. Each ATP analogue yielded three resonances: two doublets and one doublet-of-a-doublet. Assignments of resonances were based upon spin-coupling multiplets, their coupling constant magnitudes (24-27 Hz for -P-O-P- and 4-10 Hz for -P-CH2-P-), and the magnitude of the chemical shift movement during proton titration or its direction of movement. All phosphonyl resonances are substantially downfield compared to phosphoryl resonances. The chemical shifts of terminal phosphonyl units moved upfield with increasing pH or rising Mg2+ concentration. The chemical shifts of phosphonyl and phosphoryl anhydride plus ester units usually either moved downfield during proton titration and addition of Mg2+ or remained constant. Accurate pKa' values were readily determined from chemical shift movements as a function of pH: 3.05 +/- 0.04 and 8.80 +/- 0.05 for App(CH2)p, 7.34 +/- 0.06 for Ap(CH2)pp, and 8.29 +/- 0.02 for Ap(CH2)p. Addition of Mg2+ or Tris produced an acidic shift of the alkaline pKa' values. Addition of Mg2+ at pH 7.0 to the nucleotides caused large movements in the chemical shifts of their terminal two phosphorus atoms.