Pressure dependence of protein electron transfer reactions: Theory and simulation

Pressure dependence of protein electron transfer rate constant is discussed . The: rate constant is given as a product of two factors; electronic facto r (electron tunneling matrix) and nuclear factor (Franck-Condon factor). Pr essure affects the rate through both of these two factors. We analyzed effe cts of pressure on these two factors individually. The pressure dependence of the electronic factor is discussed by considering the dependence of thro ugh-space gaps in the tunneling pathway model. The effect of pressure on th e nuclear factor is discussed in terms of the Marcus expression of the Fran ck-Condon factor and the pressure dependence of the two parameters, reorgan ization energy lambda and reaction free energy Delta G, in it. We show that the dependence of lambda is generally smaller than that of Delta G. To obt ain a more quantitative picture, we carry out an analysis of pressure depen dence of through-space gaps and Delta G by normal mode simulation on cytoch rome c. In light of the results of these analyses, some experimental result s in literature on pressure effects are discussed to identify their relativ e causes.