Mixed-function oxidase is the name of a family of
oxidase enzymes
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different molecule ...
that catalyze a reaction in which each of the two atoms of
oxygen in O
2 is used for a different function in the reaction.
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
A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is use ...
electron transfer chain) or
hydrogen peroxide (
dehydrogenation of fatty acyl-CoA in
peroxisome
A peroxisome () is a membrane-bound organelle, a type of microbody, found in the cytoplasm of virtually all eukaryotic cells. Peroxisomes are oxidative organelles. Frequently, molecular oxygen serves as a co-substrate, from which hydrogen pero ...
s). Most of the oxidases are
flavoproteins.
The name "mixed-function oxidase" indicates that the enzyme oxidizes two different substrate 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
Nicotinamide adenine dinucleotide phosphate, abbreviated NADP or, in older notation, TPN (triphosphopyridine nucleotide), is a cofactor used in anabolic reactions, such as the Calvin cycle and lipid and nucleic acid syntheses, which require NAD ...
are oxidized by molecular oxygen (O
2) to produce monounsaturated fatty acyl-CoA, NADP
+ and 2 molecules of water.
Reaction
The mixed-function oxidase reaction proceeds as follows:
AH + BH
2 + O
2 --> AOH + B + H
2O (H
2O as catalyst.)
Medical significance
High levels of mixed-function oxidase activity has been studied for their activation effects in human colon carcinoma cell lines, to study the susceptibility to certain cancers. The research has been successful in mice but remains inconclusive in humans.
[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]
References
Oxidoreductases
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