The effects of pressure on yeast cytochrome c peroxidase

Abstract

The effects of pressure on cytochrome c peroxidase [CcP(FeIII)], its cyano derivative (CcP .cntdot. CN) and its enzyme-substrate complex (ES) have been studied. The effects of pressure on the binding of the substrate analog porphyrin cytochrome c (porphyrin c) to CcP .cntdot. CN and ES have also been studied. High pressure causes CcP(FeIII) to undergo a high-spin to low-spin transition but has no detectable effect on either CcP .cntdot. CN, which is already low spin, or on ES. The low-spin CcP(FeIII) structure at pressure is similar to the low-spin form at low temperature and the low-spin form of horseradish peroxidase at high pressure. .DELTA.V.degree. associated with the spin equilibrium is about 30 ml/mol and is independent of temperature. .DELTA.G.degree. is small, 4.7 kJ/mol at 0.degree. C, while .DELTA.H.degree. is 14.2 kJ/mol at 1 bar (100 kPa). Pressure has no detectable effect on the binding equilibria of mixtures of CcP .cntdot. CN plus porphyrin c or ES plus porphyrin c. This indicates that the interaction of CcP and porphyrin c results in little or no volume change; the same is true in the case of cytochrome c oxidase and porphyrin c.