Biological chemistry of carbon monoxide

Carbon monoxide (CO) has many effects in biology due to its complex biochemical activities. These actions of CO depend primarily on its ability to bind heme proteins (Hp) and to inhibit or alter their biochemical functions. Whether CO is derived from exogenous or endogenous sources, its cellular activity is related to its concentration and the concentration of molecular O(2), as well as to the availability of reduced transition metals such as Fe(II). In this respect, the CO/O(2) ratio and O(2)-dependent changes in local oxidation-reduction state assume critical importance in determining the physiological effects of CO by affecting the functions of specific Hp. By interacting with Hp, CO influences electron-transport reactions in a variety of ways, which can produce either prooxidant or antioxidant effects. Similarly, Hp relationships also govern how changes in CO concentration influence the physiological and pathological effects of nitric oxide and the relationships of the two biologically active gases to metal-catalyzed oxidations. This article provides a brief update on the biochemistry of CO as it relates to Hp binding, chemical oxidative processes, and cellular function.