Figure 16.
Schematic representation of internal electron transfer events in a bacterial VKOR homolog. The quinone cofactor is shown as a hexagon, in which blue represents a charge-transfer state. It is not known to what extent the electron-transfer steps are concerted in VKOR enzymes, i.e., whether the electron-transfer loop is simultaneously disulfide bonded to both a trx domain active-site cysteine and the partner of the charge-transfer cysteine in the transmembrane domain. For comparison with Figure 14, the trx domain is shown to the left of the transmembrane domain, but it should be noted that the trx domain is fused carboxy terminally to the transmembrane domain.