Adenylate Cyclase from Brevibacterium liquefaciens

Abstract

The stoichiometric formation of ATP from adenosine 3′ : 5′-monophosphate and PPi was established using a homogeneous adenylate cyclase preparation from Brevibacterium liquefaciens. Thermodynamic parameters were calculated based on the measurement of equilibrium constants of the reaction. The standard Gibb's free energy change (ΔG0′) for the conversion of ATP to adenosine 3′ : 5′-monophosphate and PPi varied as a function of pH and was + 0.8 to 2.1 Cal per mole between pH 7.7 and 6.2 at 25° in the presence of 5 m m MgSO4. This indicates that the formation of adenosine 3′ : 5′-monophosphate from ATP is an endergonic reaction. The standard enthalpy change of the formation of adenosine 3′ : 5′-monophosphate and PPi from ATP at pH 7.3 was determined to be +5.0 Cal per mole according to the measurement of equilibrium constants as a function of temperature. The standard entropy change of the conversion of ATP to adenosine 3′ : 5′monophosphate and PPi was calculated to be 12.4 e.u. at pH 7.3.