Mixed function oxidases are the following EXCEPT
Correct Answer: Homogentisate oxidase
Description: Ans. a (Homogentisate oxidase) (Ref. Harper's Illustrated 27th/ 97, 634; 26th ed., 89-90; 627)OXYGENASES# They catalyze the direct transfer & incorporation of oxygen into a substrate molecule.# They catalyze the incorporation of oxygen into a substrate molecule in two steps:- Oxygen is bound to the enzyme at the active site, and- The bound oxygen is reduced or transferred to the substrate.# Oxygenases are concerned with the synthesis or degradation of many different types of metabolites.# Oxygenases may be divided into two subgroups:- Dioxygenases- MonooxygenasesDioxygenasesMonooxygenases (Mixed-Function Oxidases, Hydroxylases)# Incorporate Both Atoms of Molecular Oxygen Into the Substrate# They incorporate only one atom of molecular oxygen into the substrate, the other oxygen atom is reduced to water, an additional electron donor or cosubstrate (Z) being necessary for this purpose.# Both NADH and NADPH donate reducing equivalents for the reduction of these cytochromes, which in turn are oxidized by substrates in a series of enzymatic reactions collectively known as hydroxylase cycle.# Examples include the:- Liver enzymes,- Homogentisate- Dioxygenase (oxidase) and- 3-hydroxyanthranilate dioxygenase (oxidase), that contain iron; and- L-tryptophan dioxygenase (tryptophan pyrrolase), that utilizes heme.# In liver microsomes, cytochromes P450 are found together with cytochrome b5 and have an important role in detoxification.# Cytochromes P450 are heme-containing monooxygenases important for the detoxification of many drugs & for the hydroxylation of steroids.# Cytochrome P450 is considered the most versatile biocatalyst known. It has been shown by the use of 18O2 that one atom of oxygen enters R-OH and one atom enters water. This dual fate of the oxygen accounts for the former naming of monooxygenases as "mixed function oxidases."# Benzpyrene, aminopyrine, aniline, morphine, and benzphetamine are hydroxylated, increasing their solubility and aiding their excretion.# Mitochondrial cytochrome P450 systems are found in steroidogenic tissues such as adrenal cortex, testis, ovary, and placenta and are concerned with the biosynthesis of steroid hormones from cholesterol (hydroxylation at C22 and C20 in side-chain cleavage and at the 11 and 18 positions).# In addition, renal systems catalyzing la - and 24 hydroxylations of 25-hydroxycholecalciferol in vitamin D metabolism--and cholesterol 7a-hydroxylase and sterol 27-hydroxylase involved in bile acid biosynthesis in the liver are P450 enzymes.Oxidoreductases have a variety of functions in metabolism:# Oxidases and dehydrogenases play major roles in respiration;# Hydroperoxidases protect the body against damage by free radicals; and# Oxygenases mediate the hydroxylation of drugs and steroids.Also Note: Tissues are protected from oxygen toxicity caused by the superoxide free radical by the specific enzyme superoxide dismutase.
Category:
Biochemistry
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