ABSTRACT
Reduction is the reverse of oxidation and therefore it can involve loss of an oxygen atom or the addition of two hydrogen atoms. Many of the same enzymes that are involved in oxidation can also mediate reductions. Much reduction occurs in anaerobic bacteria in the gut because, being anaerobic, much of the metabolism of the organisms involves reductive pathways. Carbon tetrachloride is a solvent that is chemically inert, highly resistant to oxidation, but biologically toxic. Despite its chemical stability, cytochrome P450 is able to convert carbon tetrachloride to several reactive species. Trichloromethyl radical can undergo a second one-electron reduction to generate the trichloromethyl anion followed by protonation to yield chloroform. Cytochrome P450-containing enzyme systems are not the only enzymes that are effective in reducing nitrogen-containing functional groups. Quinones are very common reactive metabolites of drugs and other xenobiotics. Although quinones appear structurally similar to ketones, their reduction is not usually mediated by keto reductases.
