Table 1.

Measured back ET rate constants for the fast kinetic phase in solution and in crystals, and donor-acceptor distances from crystal structures. The relative mean-squared electronic couplings from the PATHWAY model with respect to the WT values appear in the last column. ${\langle H_{DA}^2\rangle }_{rel}=\langle H_{DA}^2\rangle /{\langle H_{DA}^2\rangle }^{WT}$ based on Fe-to-ZnP tunneling.

	Crystal Data a		Soln Datab	PWc
	keb (s−1)	RZn–Fe (Å)	Red–ed (Å)	Rtrp-heme (Å)	keb (s−1)	${\langle H_{DA}^2\rangle }_{rel}$
WT	6,000	26.5	15.6	13.6	4,900	1
F82W	5,800	26.4	15.6	14.0	--	1.0
F82S	2,000	26.3	15.4	13.5	2,500	1.0
F82I	2,100	29.8	22.6	19.4	1,900	0.02
F82Y	4,000	29.4	22.8	19.6	4,300	0.003

^aAll taken from Ref. 7.

^bAll are taken from Ref. 17.

^cHeme-ZnP PATHWAY couplings