Mixed-function oxidase

Mixed-function oxidase is the name of a family of oxidase enzymes that catalyze a reaction in which each of the two atoms of oxygen in O₂ is used for a different function in the reaction.^[1]

Oxidase is a general name for enzymes that catalyze oxidations in which molecular oxygen is the electron acceptor but oxygen atoms do not appear in the oxidized product. Often, oxygen is reduced to either water (cytochrome oxidase of the mitochondrial electron transfer chain) or hydrogen peroxide (dehydrogenation of fatty acyl-CoA in peroxisomes). Most of the oxidases are flavoproteins.

The name "mixed-function oxidase" indicates that the enzyme oxidizes two different substrates simultaneously. Desaturation of fatty acyl-CoA in vertebrates is an example of the mixed-function oxidase reaction. In the process, saturated fatty acyl-CoA and NADPH are oxidized by molecular oxygen (O₂) to produce monounsaturated fatty acyl-CoA, NADP⁺ and 2 molecules of water.

Reaction

The mixed-function oxidase reaction proceeds as follows:

AH + BH₂ + O₂ --> AOH + B + H₂O (H₂O as catalyst.)

Medical significance

High levels of mixed-function oxidase activity have been studied for their activation effects in human colon carcinoma cell lines,^[2] to study the susceptibility to certain cancers. The research has been successful in mice but remains inconclusive in humans.^[3]

References

^ Mixed+Function+Oxygenases at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
^ Moskwa PS, Vadi H, and Drewinko B, Mixed Function Oxidase Activities of Established Human Colon Carcinoma Cell, 45, 5447-5451, November 1985
^ Kellerman G, Jett JR, Luyten-Kellermann M, Moses HL, Variation of microsomal mixed function oxidase(s) and human lung cancer, Cancer (Impact Factor: 5.2). 06/2006; 45(6):1438 - 1442. DOI: 10.1002/1097-0142(19800315)45:6

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[1] Mixed+Function+Oxygenases at the U.S. National Library of Medicine Medical Subject Headings (MeSH)

[2] Moskwa PS, Vadi H, and Drewinko B, Mixed Function Oxidase Activities of Established Human Colon Carcinoma Cell, 45, 5447-5451, November 1985

[3] Kellerman G, Jett JR, Luyten-Kellermann M, Moses HL, Variation of microsomal mixed function oxidase(s) and human lung cancer, Cancer (Impact Factor: 5.2). 06/2006; 45(6):1438 - 1442. DOI: 10.1002/1097-0142(19800315)45:6

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v t e Enzymes
Activity	Active site Binding site Catalytic triad Oxyanion hole Enzyme promiscuity Diffusion-limited enzyme Cofactor Enzyme catalysis
Regulation	Allosteric regulation Cooperativity Enzyme inhibitor Enzyme activator
Classification	EC number Enzyme superfamily Enzyme family List of enzymes
Kinetics	Enzyme kinetics Eadie–Hofstee diagram Hanes–Woolf plot Lineweaver–Burk plot Michaelis–Menten kinetics
Types	EC1 Oxidoreductases (list) EC2 Transferases (list) EC3 Hydrolases (list) EC4 Lyases (list) EC5 Isomerases (list) EC6 Ligases (list) EC7 Translocases (list)