Proton Activities for Three States of Cytochrome P-450cam
David Dolphin, James, B.R., and Welborn, H.C.
Biochem. Biophys. Res. Commun.
Changes in proton concentration during the binding of O2, CO, and in the exchange of O2 by CO at ferrocytochrome P 450cam were measured by direct titration Insufficient proton release was observed to support protonation-deprotonation of an axial cysteinyl S donor as a mechanism for generation of hyper spectra in only the carbonylated ferrous state. Measurement of the pCO2 required to convert 1/2 of the cytochrome to the CO-bound form as a function of pH (the CO Bohr effect) confirmed the direct titration data.