A thin-film electrochemical study of the "blue" copper proteins, auracyanin A and auracyanin B, from the photosynthetic bacterium Chloroflexus aurantiacus: the reduction potential as a function of pH

Abstract

The reversible formal potentials of auracyanin A and auracyanin B, two closely related "blue" copper proteins from the photosynthetic bacterium Chloroflexus aurantiacus, have been determined by protein film voltammetry in the range 4<or=pH<or=9. At pH 7 in 0.1 M NaCl, the values of for auracyanin A and auracyanin B are 205+/-7 mV and 215+/-7 mV, respectively, versus the standard hydrogen electrode. In both cases there is a smooth but non-sigmoidal change in from approximately 190 mV at pH 9 to approximately 240 mV at pH 4. The small changes in as a function of pH indicate that auracyanin A and auracyanin B differ from those "blue" copper proteins in which the Cu site in the reduced (Cu(I)) state switches to a redox-inhibited form at low pH. For auracyanin A, the results obtained by protein film voltammetry are closely similar to those obtained by the conventional spectroelectrochemical method. The findings are discussed in relation to the putative role of auracyanin in biological electron transfer.

Probing biological redox chemistry with large amplitude Fourier transformed ac voltammetry

“… 78 This structurally-simple, mono-copper containing electron-transfer protein has been extensively investigated with dcV and represents something of a model system for biological one-electron transfer, with the copper center capable of rapidly transitioning between the +1 and +2 oxidation states. 16 , 30 , 78 – 80 …”

A cytochrome c551 mediates the cyclic electron transport chain of the anoxygenic phototrophic bacterium Roseiflexus castenholzii

“…This value was consistent with the previously reported midpoint potential of Ac (+246 mV at pH 7) ( Tsukatani et al., 2009 ) and was similar to reported potentials of C . aurantiacus Ac-A and Ac-B (+205 mV and +215 mV, respectively, at pH 7) ( Rooney et al., 2003 ). The redox midpoint potential E m values of the rc RC heme cofactors were determined to be +73.5 mV and +269.6 mV ( Supplemental Figure 3C ), which were adequate for transferring electrons from rc Ac to the c -type hemes in the rc RC.…”