ELECTRON-TRANSPORT NETWORKS IN MULTICENTER METALLOPROTEINS

Electron transfer (ET) in multicentre proteins exhibits cooperativity, i.e. mutual electrostatic, spectral, and structural interactions betw een the individual ET centres. We investigate here two kinds of cooper ativity. The first is ''static'' and is represented by the electrostat ic interaction between two charged centres inside or outside a solvate d dielectric globule. Such effects can be the origin of interaction re duction potentials and also provide a basis for calculation of the pro tein and solvent reorganization Gibbs energy of intramolecular and int ermolecular ET. Cooperativity effects in the second class are ''dynami c'' and originate from partial vibrational relaxation of intermediate states in multistep ET. This leads to coherence in the ET sequence. Th e concepts and formalism are applied to the ET patterns of the two-hem e cytochrome c4, four-heme cytochrome c3, and the bacterial photosynth etic reaction centre. It is shown that cooperativity in the approximat ely thermoneutral ET steps of the cytochromes is likely to be ''static '' while the activationless nature of the photosynthetic ET steps can also lead to coherence in the overall ET sequence.