Redox-linked transient deprotonation at the binuclear site in the aa3-type qunol oxidase from Ac.dianus ambivalens: Implications for proton translocation

摘要

The hyperthermophilic archaeon Acidianus ambivalens expresses a membrane-bound aa3-type quinol ox- idase, when grown aerobically, that we have studied by reso- nance Raman spectroscopy. The purified aa3 oxidase, which does not contain bound quinol, undergoes a reversible slow conformational change at heme a3 upon reduction, as indi- cated by a change in the frequency of its heme formyl stretching mode, from 1,660 cm-1 to I,667 cm-1. In contrast, upon reduction of the integral membrane enzyme or the Furified enzyme preincubated with decylubiquinol, this mode appears at l,667 cm-1 much more rapidly, suggesting a role of the bound quinol in controlling the redox-linked confor- mational changes. The shift of the formyl mode to higher frequency is attributed to a loss of hydrogen bonding that is associated with a group having a pKa of appro = 3.8. Based on these observations, a crucial element for proton translocation in- volving a redox-linked conformational change near the heme a3 formyl group is postulated.