Complexes of divalent manganese with adenosine triphosphate and other nucleotides have been investigated by magnetic resonance techniques. Proton magnetic resonance broadening techniques have been used to quantitatively determine the spin–spin relaxation time (T2), for water protons in Mn2+–nucleotide solution. T2 relaxation times were also measured for the proton resonances of the purine ring in ATP, ADP, AMP-5′, and polyadenylic acid, and for the pyrimidine ring protons of CTP and CMP-5′ in Mn2+ solutions. Electron spin resonance studies gave equilibrium constants for Mn2+–nucleotide complexes and enabled observation of the electron spin relaxation of the Mn2+ ion when complexed with nucleotides. From water proton T2 relaxation times, it has been possible to calculate the number of binding sites of Mn2+ on the nucleotide. A value of between two and three was obtained for the 5′-triphosphates, whereas, for the corresponding 5′-monophosphates, a value of one is obtained. It has been concluded that in the Mn2+–ATP complex and probably the other nucleoside triphosphate complexes, the binding of the metal ion to ring positions is negligible.
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