Biochemistry - The Chemical Reactions of Living Cells, Volume 2 - D. Metzler 1980

How electrons encounter oxygen, how ATP is generated in the process, and some related phenomena
Oxygenases and hydroxylases

For many years, biochemical oxidation was associated primarily with the removal of hydrogen. It was always assumed that the oxygen found in organic substances invariably originated from Water molecules. A water molecule can add across a double bond, and the resulting alcohol is then subjected to the action of dehydrogenases. Nevertheless, occasional reports indicated that small amounts of O₂ are essential and required even for Cells growing under anaerobic conditions [134]. In 1955, Hayaishi and Mason independently demonstrated that ¹⁸O is sometimes incorporated into Organic compounds directly from ¹⁸O₂, as shown in equation (10-43). Today, we know of A large number of oxygenases involved in the synthesis of vital metabolic compounds such as sterols, Prostaglandins, and biologically active vitamin D derivatives. Oxygenases are also essential for the Catabolism of numerous substances, most frequently acting on non-polar groups that are otherwise resistant to the action of Other Enzymes [134–136].

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Oxygenases are classified into Dioxygenases and Monooxygenases ("mixed-function oxidases"). Monooxygenases are also referred to as hydroxylases. Dioxygenases catalyze the incorporation of both oxygen atoms into the molecule, as shown in equation (10-43), whereas monooxygenases incorporate only one atom. The other oxygen atom of the O₂ molecule is reduced to water. A typical monooxygenase reaction is the hydroxylation of an alkane to an alcohol:

СН₃—(СН₂)_n—СН_{3 +}O₂ + ВН₂→ СН₃—(СН₂)_n—СН₂OН + Н₂O + В. (10-44)

A characteristic property of monooxygenases is the requirement for an additional reduced substrate, or cosubstrate [BH₂ in equation (10-44)], which reduces the second atom of the O₂ molecule to H₂O.