Table 2.

Comparison of predicted values of electronic coupling with experimentally-determined values.

Predicted values determined from the structurea
Donor	Acceptor	Relative HAB
Direct single-step tunneling
preMADH βTrp108	MauG 6-coordinate heme	1.0
Tunneling segments in Trp199-mediated hopping
preMADH βTrp108	MauG Trp199	1837
MauG residue 199	MauG 6-coordinate heme	1317
Experimentally determined valueb		1400–1600

^aThe HARLEM computer program (30) was used to calculate relative values of H_AB from the crystal structures of the MauG-preMADH complex using the direct distance approach Dutton and coworkers (4). These H_AB values are dimensionless and therefore cannot be directly compared to the experimentally determined values. However, relative values for putative hopping segments and the single-step direct tunneling path can be compared with the experimental values. For ease of comparison all values were normalized to that for the H_AB value for the overall ET reaction; the shortest distance between an atom of residue βTrp108 of preMADH and the 6-coordinate heme of MauG.

^bCalculated from the values presented in Table 1.