Pem. Siegbahn et al., A COMPARISON OF ELECTRON-TRANSFER IN RIBONUCLEOTIDE REDUCTASE AND THEBACTERIAL PHOTOSYNTHETIC REACTION-CENTER, Chemical physics letters, 292(4-6), 1998, pp. 421-430
The energy requirements for electron transfer in two different protein
s are compared, based on quantum chemical calculations. The methods us
ed are the hybrid density functional B3LYP combined with dielectric ca
vity models to account for the effects of the polarizable protein. The
experimental exothermicities for the electron transfer steps from the
chlorophyll special pair both to the pheophytin and to the quinone ar
e well reproduced. For ribonucleotide reductase (RNR), the same method
s in contrast predict a large endothermicity for the electron transfer
from the cysteine at the substrate site to the tyrosyl radical in the
interior of the protein. This indicates that another type of process
is active in RNR. Previous work has suggested that this process is hyd
rogen atom transfer. (C) 1998 Elsevier Science B.V. All rights reserve
d.