TABLE 2.

Pathways model estimates for the electron transfer reaction from heme a to heme a₃ in the crystallographic and equilibrium conformations.

Pathway	Steps	kET, s−1 (cryst.)	kET, s−1 (equil.)
Covalent	16 + 0 + 0	8 × 106	8 × 106
Direct	10 + 0 + 1	7 × 106	7 × 107
Via AlaA375	15 + 1 + 0	1 × 106	3 × 105
Via ArgA438	16 + 2 + 0	2 × 105	2 × 106

The second column shows the numbers of covalent steps, hydrogen bond steps, and through-space jumps in each pathway. The steps are counted from Fe of heme a to Fe of heme a3.