Investigation of Electron Tunneling Between Cytochrome c Peroxidase and Cytochrome c

Abstract

The nature of electron transfer between the bound complex cytochrome c and cytochrome c peroxidase has been investigated. Experimental verification of the predicted charge-transfer band provides evidence of electron tunneling as the mechanism of transfer between these molecules in solution at room temperature. The measured transfer distance is ≃ 7 angstroms between heme edges, which results in a distance of ≃ 15 to 20 angstroms between iron atoms.

Direct measurements of intramolecular electron transfer rates between cytochrome c and cytochrome c peroxidase: effects of exothermicity and primary sequence on rate.

“…By assuming kt 104 s-1 as predicted by Potasek (15), we attempted to measure this rate directly using the following scheme: (21). ¶ Since the geminate recombination rate constant, kco, is =5 s-1 at pH 7.0 (21), we expected electron transfer to compete favorably with CO recombination.…”

“…Rapid mixing of ferrocytochrome c peroxi- sition (15). Corroboration of this rate by a more direct measurement is desirable in the context of understanding biological electron transfer rates.…”

“…However, AP for this reaction is very large (0.9 V) (12). A recent study also inferred fast electron transfer (kt = 2.7 x 104 s-1) from cyt c peroxidase(II) to cyt c(III) (AE sition (15) (18). The product was purified by G-200 Abbreviations: cyt c, cytochrome c; Por, porphyrin.…”

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ABSTRACTRapid mixing of ferrocytochrome c peroxi- sition (15). Corroboration of this rate by a more direct measurement is desirable in the context of understanding biological electron transfer rates.

We, therefore, wish to report the direct measurement of electron transfer from cyt c peroxidase(II) to cyt c(III) within the cyt c(III)-cyt c peroxidase(II) complex.

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“…Samples for pulse radiolysis were prepared by mixing equal concentrations (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) AM) of cyt c peroxidase(III) and cyt c(III) in phosphate buffer (1 mM, pH 7.0). The solutions were degassed under Ar and transferred by syringe to anaerobic quartz cells for pulse radiolysis.…”