Electron transfer and transport through multi-heme proteins: recent progress and future directions

I review recent experimental measurements probing electron transfer (ET) and electron transport (ETp) through multi-heme cytochromes (MHCs) as well as their theoretical interpretation. Examples include pump-probe spectroscopy of Ru-labeled MHCs aimed at determining heme-heme ET rates in MHCs and the measurement of the I-V characteristics of MHCs in bioelectronic junctions. While the ET mechanism appears to be well established for MHCs in aqueous solution, the ETp mechanism in bioelectronic junctions such as STM remains elusive partly due to the complexities of the electrode-protein interface.