The free energy change associated with the hydrolysis of the thiol ester bond of acetyl coenzyme A

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Abstract
Three partially independent calculations are reported for the free energy of hydrolysis of acetyl coenzyme A, using free-energy data previously reported by Burton and Krebs (1953). The 3 calculations are based on the equilibria of (a) the condensing enzyme system, (b) phosphotransacetylase, and (c) the acetaldehyde-oxidizing system of Clostridium kluyveri. The values obtained at pH7 are G'' = -7.38, -8.7 and -8.25 kcal., respectively, and are considered to be reasonably consistent. At present, a value of about -8.2 kcal. appears to be the most reliable. This is consistent with the phosphotransacetylase data and a slightly revised value of G'' = -8.9 kcal. for the hydrolysis of the terminal pyrophosphate group of adeno-sine triphosphate at pH 7.5. Revised values for the free energies of formation (A G[degree]f) of the citrate, 3-cis-aconitate3- and D-isocitrate3-ions are respectively - 279.36, -220.63 and -277.77 kcal.
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