Pressure-induced effects on cytochrome oxidase: the aerobic steady state.

If cytochrome c oxidase is subjected to pressure during the aerobic steady state, large spectral changes are apparent. These seem to be associated with the inhibition of electron transport within the oxidase. The volume change for the transition is about 80 mL/mol. When the oxidase in the aerobic steady state, with porphyrin cytochrome c (the iron-free derivative of cytochrome c) bound to it, is subjected to pressure, the porphyrin derivative is released. This results from a change in the dissociation constant of the complex. Whereas the dissociation constant during turnover is about 1.25 X 10(-8) M, during pressure-induced inhibition the dissociation constant appears to be about an order of magnitude greater. It appears as though the binding site of the inhibited, partially reduced enzyme more closely resembles that of the fully reduced enzyme than that of the enzyme during the aerobic steady state.