Heme-dependent monooxygenases

A superfamily of heme-dependent monooxygenases that utilize molecular oxygen and NADPH. These enzymes are localized in the endoplasmic reticulum, and are often used as a marker for microsomal fractions obtained upon homogenization of cells. Especially abundant in hver, cytochrome P-450 enzymes play a major role in detoxifi-... 

Heme-dependent monooxygenases contain ferric protoporphyrin IX, the heme, as the cofactor and protect us from the xenobiotics, toxins, food, and chemicals we take up. As these proteins exhibit a very strong absorption band maximum at... 

The systems where this type of reaction is produced may be metal-, heme- or flavin-dependent. In flavin-dependent monooxygenases, a flavin-oxygen intermediate reacts with the substrate, producing water in a second step and requiring cofactors for regeneration of the flavin moiety. The non-heme-dependent oxygenases include the... 

This enzyme [EC 1.6.2.4] (also referred to as NADPH ferrihemoprotein reductase, NADPHxyto-chrome P450 reductase, TPNH2 cytochrome c reductase, and ferrihemoprotein P450 reductase) catalyzes the reaction of NADPH with two ferricytochrome to produce NADP+ and two ferrocytochrome. The protein requires FMN and FAD. In addition, it also catalyzes the reduction of heme-thiolate-dependent monooxygenases (e.g.,... 

The monooxygenase group of enzymes includes the non-P450 hydroxylases which catalyze the insertion of a hydroxyl group to replace a hydrogen atom at a saturated carbon [6-8] and the non-heme-dependent oxygenases such as the flavin-molybdenum-cobalt-dependent xanthine oxidase and aldehyde oxidase... 

Cytochrome P-450-dependent monooxygenases Lipoxygenases (non-heme Fe-dependent) L M M... 

The isolation of many monooxygenase systems has meanwhile greatly facilitated our understanding of their reaction mechanisms. Of major importance is the conciusion that all heme-sulfur dependent monooxygenases proceed by the same reaction cycle and that only the electron transport system may differ. Essentially five steps are involved in the reaction cycle. These will be discussed sequentiaily. 

Among metallooxygenases the most extensively studied remains cytochrome P-450. Cytochrome P-450 dependent monooxygenase is a family of heme-iron enzymes which catalyze the transfer of one oxygen atom from dioxygen into a wide variety of substrates according to reaction ... 

Oxidation (the introduction of another phenolic hydroxyl group) is effected by A -methylcoclaurine 3 -monooxygenase (EC 1.14.13.71), the gene for which (CYP80B1) produces a heme-thiolate cytochrome P4so-dependent monooxygenase protein that uses reduced NADPH as a cofactor and oxygen ( ) to produce water, oxidized cofactor (nicotinamide adenine dinucleotide [NADP ]), and (5)-3 -hydroxy-A-methylcoclaurine. 

Figure 8. Reaction catalyzed by pterine-dependent non-heme iron monooxygenases [93].

This heme-thiolate-dependent enzyme [EC 1.14.15.4], also known as steroid 11/3-monooxygenase, catalyzes the reaction of a steroid with reduced adrenal ferredoxin and dioxygen to produce an 11/3-hydroxysteroid, oxidized adrenal ferredoxin, and water. The enzyme also catalyzes the hydroxylation of steroids at the 18-position and can catalyze the conversion of 18-hydroxycorticosterone into aldosterone. 

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