Reports

Electron-Tunneling Pathways in Cytochrome c

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Science  15 May 1992:
Vol. 256, Issue 5059, pp. 1007-1009
DOI: 10.1126/science.256.5059.1007

Abstract

Distant Fe2+-Ru3+ electronic couplings have been extracted from intramolecular electrontransfer rates in Ru(histidinex) (where X = 33, 39, 62, and 72) derivatives of cytochrome c. The couplings increase according to 62 (0.0060) < 72 (0.057) < 33 (0.097) < 39 (0.11 per wave numbers); however, this order is out of line with the histidine to heme edge-edge distances [62 (14.8) > 39 (12.3) > 33 (11.1) > 72 (8.4 angstroms)]. The rates (and the couplings) correlate with the lengths of σ-tunneling pathways comprised of covalent bonds, hydrogen bonds, and through-space jumps from the histidines to the heme group. Space jumps greatly decrease couplings: One from Pro71 to Met80 extends the σ-tunneling length of the His72 pathway by roughly 10 covalent-bond units.