Many chemical reactions involve electron exchanges, and these usually occur when molecules react in a collision. However, it was discovered over thirty years ago that redox centers 10 to 20 Å apart could rapidly exchange electrons in the " redox enzymes " and " bioenergetic systems " of all living things. These long-distance electron transfers have been the subject of a large number of theoretical and experimental studies. We now know that they play an essential role in the catalytic mechanism of these enzymes, and we know the factors that determine their speed. Mysteries remain, however. In the many redox enzyme structures that have been determined in recent years, " electron transfer chains " consisting of several redox centers separated by a distance of 10 to 20 Å can be clearly distinguished. However, the order of the redox potentials of the centers along these chains is not always conducive to rapid, almost unidirectional transfers. This raises the question of whether these are " limiting " in the catalytic cycle and whether they play a role in the enzyme's " catalytic bias " , i.e. its ability to catalyze one reaction better than the opposite reaction.
These points were discussed during the seminar. First, we explained the factors that determine the value of the electron transfer rate constant, and why electron transfer takes place over long distances in redox enzymes. We then presented the methods that have been developed in recent years to measure this rate in "respiratory" enzymes, and analyzed the data obtained for several enzymes with potential applications in biotechnology.
