Thermochemistry of the reactions between adenosine, adenosine 5'-monophosphate, inosine, and inosine 5'-monophosphate; the conversion of L-histidine to (urocanic acid + ammonia)

Article abstract of DOI:10.1006/jcht.1993.1009

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: Δ_rH_m^o = -(49.6 +/- 0.5) kJ*mol^-1 for AMP^2-(aq) + H2O(l) + H⁺(aq) = HIMP^2-(aq) + NH4⁺(aq); Δ_rH_m^o = -(49.4 /- 0.7) kJ*mol^-1 for adenosine(aq) + H2O(l) + H⁺(aq) = inosine(aq) + NH4⁺(aq); Δ_rG_m^o = -(13.0 +/- 0.4) kJ*mol^-1, Δ_rH_m^o = (0.9 +/- 0.4) kJ*mol^-1, and Δ_rS_m^o = (47 +/- 2) J*K^-1*mol^-1 for AMP^2-(aq) + H2O(l) = adenosine(aq) + HPO4^2-(aq); Δ_rG_m^o = -(12.6 +/- 0.1) kJ*mol^-1, Δ_rH_m^o = (1.2 +/- 0.2) kJ*mol^-1, and Δ_rS_m^o = (48 +/- 1) J*K^-1*mol^-1 for HIMP^2-(aq) + H2O(l) = inosine(aq) + HPO4^2-(aq); and Δ_rG_m^o = -(2.5 +/- 0.7) kJ*mol^-1, Δ_rH_m^o = (7.6 +/- 0.8) kJ*mol^-1, and Δ_rS_m^o = (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.