Microcalorimetry and high-performance liquid chromatography (h.p.l.c) have been used to conduct a thermodynamic investigation of the following nitrilase catalyzed reactions: (1) benzonitrile(aq) + 2H(2)O(1) = benzoic acid(aq) + ammonia(aq), (2) benzylcyanide(aq) + 2H(2)O(1) = benzeneacetic acid(aq) + ammonia(aq), (3) 3-phenylpropionitrile(aq) + 2H(2)O(1) = 3-phenylpropanoic acid(aq) + ammonia(aq), (4) 4-phenylbutyonitrile(aq) + 2H(2)O(1) = 4-phenylbutyric acid(aq) + ammonia(aq), (5) alpha-methylbenzyl cyanide(aq) + 2H(2)O(1) = alpha-methylbenzene acetic acid(aq) + ammonia(aq), and (6) 3-indoleacetonitrile(aq) + 2H(2)O(1) = indole-3-acetic acid(aq) + ammonia(aq). The equilibrium measurements showed that these reactions proceeded to completion. Thus, it was possible to set only lower limits for the values of the apparent equilibrium constants K'. However, it was possible to obtain precise values of the calorimetrically determined molar enthalpies of reaction Delta(r)H(m)(cal). These values were then used in conjunction with an equilibrium model to calculate values of the standard molar enthalpies for chemical reference reactions that correspond to the above overall biochemical reactions. (c) 2004 Elsevier Ltd. All rights reserved.