Origin of life considerations can be useful for understanding function and mechanism in metabolism of present cofactors. An important role is postulated for chromanols such as tocopherol in the transition from anaerobic to aerobic metabolism, this transition being a critical point in evolution. The antioxidant and amphipathic properties of such molecules make them plausible candidates for dioxygen detoxification within membranes of the earliest respiratory systems. In the light of this, the possibility is examined that tocopherol still plays such a role of a detoxicating dioxygen carrier within membranes. In addition, a mechanism for vitamin K-dependent carboxylation is suggested in line with the proposal for vitamin E and in accord with the present state of experimental knowledge.