title: Thermodynamics of the conversion of penicillin G to phenylacetic acid and 6-aminopenicillanic acid.
abstract: The thermodynamics of the enzymatic conversion (penicillin acylase) of aqueous penicillin G to phenylacetic acid and 6-aminopenicillanic acid have been studied using both high-pressure liquid-chromatography and microcalorimetry. The reaction was carried out in aqueous phosphate buffer over the pH range 6.0-7.6, at ionic strengths from 0.10 to 0.40 mol kg-1, and at temperatures from 292 to 322 K. The data have been analyzed using a chemical equilibrium model with an extended Debye-Hückel expression for the activity coefficients. For the reference reaction, penicillin G- (aq) + H2O(l) = phenylacetic acid-(aq) + 6-aminopenicillanic acid-(aq) + H+ (aq), the following parameters have been obtained: K = (7.35 +/- 1.5) X 10(-8) mol kg-1, delta G0 = 40.7 +/- 0.5 kJ mol-1, delta H0 = 29.7 +/- 0.6 kJ mol-1, and delta C0p = -240 +/- 50 J mol-1 K-1 at 298.15 K and at the thermochemical standard state. The extent of reaction for the overall conversion is highly dependent upon the pH.
authors.affiliation: Chemical Thermodynamics Division, National Bureau of Standards, Gaithersburg, MD 20899.
authors.forename: Y B
authors.initials: YB
authors.lastname: Tewari
authors.forename: R N
authors.initials: RN
authors.lastname: Goldberg
mesh_terms: D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010397:Penicillanic Acid / Q000031:analogs & derivatives; D010400:Penicillin G; D010648:Phenylacetates; D013816:Thermodynamics
chemical_list: D010648:Phenylacetates; D010397:Penicillanic Acid; C025136:phenylacetic acid; D010400:Penicillin G; C004408:aminopenicillanic acid