Electron transfer in DNA? Competition by ultra-fast proton transfer?

Interstrand proton transfer, which is driven by the large changes in acidity or basicity that result from loss or uptake of an electron from or by a base in a base pair of DNA, can constitute a very powerful stop to the migration of holes or electrons in the direction of the DNA helix via the stacked bases. In theory, such a proton transfer could have the same rate (10(14) s(-1)) as the electron transfer. In base pair model systems, proton transfer rates up to 10(13) s(-1) have been measured. As a result of the existence of proton transfer barriers to electron transfer, the migration distance of the charge carriers in DNA is likely to be short, extending over only less than or equal to 5 bp's (17 Angstrom).