Thermodynamic Parameters of pH-dependent Optical Transition in Bovine Heart Cytochrome c Oxidase

Abstract

Cytochrome c oxidase was prepared according to the method of Yonetani (1961), The pH-induced optical transition in the oxidised (resting) enzyme was studied between 400 and 500 nm at different temperatures, The changes in 'enthalpy, entropy and free energy for the transition were determined to be -37.89 ± 6.20KJ/mole, - 158.16 ± 8.20 JK" mole" and -41.60KJ/inole respectively. The results are discussed in terms of the binding of a strong ligand (possibly histidine) to the distal side of an already pentacoordinate high spin cytochrome as.