TABLE 2.
Driving forces, ∆G (eV), for the individual reduction steps in the catalytic cycle, as obtained from the present calculations, assuming that the tyrosine is left unprotonated until the last reduction step. Note that the first column shows only the cofactor reduced in each particular step, not the full BNC. Rate-limiting barriers, ∆G# (eV), estimated from experimental information are also given for each step. The effects on the driving forces and the barrier heights of the presence of the electrochemical gradient across the membrane are also given.
| No gradient | With gradient: 0.2 V Four protons pumped | |||
|---|---|---|---|---|
| Reduction process | ∆G (eV) calc | ∆G # (eV) est | ∆G (eV) calc | ∆G # (eV) est |
|
P
M →F: CuB(II)OH → CuB(I)OH2 F →O H: Fea3(IV)=O → Fea3(III)OH O H →E H: Fea3(III)OHTyrO• → Fea3(II/III)OH2TyrO•/− E H →R: Fea3(II/III)OH2TyrO•/− → Fea3(II)OH2TyrOH |
−0.80 | +0.58 | −0.40 | +0.65 |
| −0.43 | +0.58 | −0.03 | +0.65 | |
| −0.40 | +0.58 | −0.00 | +0.65 | |
| −0.25 | +0.58 | +0.15 | +0.65 | |
|
R →A: O2 binding A →P M: O-O cleavage |
−0.02 | +0.45 | −0.02 | +0.60 |
| −0.30 | +0.55 | −0.30 | +0.68 | |
| Sum | −2.2 | −0.60 | ||