- Thermochemistry of the reactions between adenosine, adenosine 5'-monophosphate, inosine, and inosine 5'-monophosphate; the conversion of L-histidine to (urocanic acid + ammonia)
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Results of equilibrium and calorimetric measurements are reported for a series of enzyme-catalyzed reactions involving the deamination of adenosine 5'-monophosphate (AMP), adenosine, and L-histidine, and the dephosphorylation of AMP and inosine 5'-monophosphate (IMP).These measurements have been analyzed with a model which describes the complex equilibria in solution.The results obtained are: ΔrHmo = -(49.6 +/- 0.5) kJ*mol-1 for AMP2-(aq) + H2O(l) + H+(aq) = HIMP2-(aq) + NH4+(aq); ΔrHmo = -(49.4 /- 0.7) kJ*mol-1 for adenosine(aq) + H2O(l) + H+(aq) = inosine(aq) + NH4+(aq); ΔrGmo = -(13.0 +/- 0.4) kJ*mol-1, ΔrHmo = (0.9 +/- 0.4) kJ*mol-1, and ΔrSmo = (47 +/- 2) J*K-1*mol-1 for AMP2-(aq) + H2O(l) = adenosine(aq) + HPO42-(aq); ΔrGmo = -(12.6 +/- 0.1) kJ*mol-1, ΔrHmo = (1.2 +/- 0.2) kJ*mol-1, and ΔrSmo = (48 +/- 1) J*K-1*mol-1 for HIMP2-(aq) + H2O(l) = inosine(aq) + HPO42-(aq); and ΔrGmo = -(2.5 +/- 0.7) kJ*mol-1, ΔrHmo = (7.6 +/- 0.8) kJ*mol-1, and ΔrSmo = (34 +/- 4) J*K-1*mol-1 for L-histidine(aq) = urocanate-(aq) + NH4+(aq).These results are discussed in relation to both thermodynamic-cycle calculations involving these substances and other reactions of a chemically similar nature.
- Larson, J. W.,Tewari, Y. B.,Goldberg, R. N.
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