ABSTRACT: The pH dependence of the Fe(III) reduction potential, E(0)', for yeast cytochrome c peroxidase (yCcP) and three distal pocket mutants, CcP(H52L), CcP(H52Q), and CcP(R48L/W51L/H52L), has been determined between pH 4 and 8. E(0)' values at pH 7.0 for the yCcP, CcP(H52L), CcP(H52Q), and CcP(R48L/W51L/H52L) are -189, -170, -224, and -146mV, respectively. A heme-linked ionization in the reduced enzyme affects the reduction potential for yCcP and all three mutants. Apparent pK(A) values for the heme-linked ionization are 7.5±0.2, 6.5±0.3, 6.4±0.2, and 7.0±0.3 for yCcP and the H52L, H52Q, and R48L/W51L/H52L mutants, respectively. A cooperative, two-proton ionization causing a spectroscopically-detectable transition was observed in the ferrous states of yCcP, CcP(H52L) and CcP(H52Q), with apparent
