Steroid monooxygenases

Steroid monooxygenase Cylindrocarpon radicicola ATCC 11011 1 2 identical subunits NADPH 115 (56 each) 1 FAD per subunit 7.8 [83]... 

Another way of altering the substrate specificity of PAMO was shown in 2012 by creating some chimeric biocatalysts [38]. Thus, using structure-inspired subdomain exchange, PAMO was blend with CHMO. or steroid monooxygenase (STMO) from Rhodococcus rhodochrous. For this, 106 amino acids corresponding to the... 

Proton Pump Inhibitors and Acid Pump Antagonists retinoid X receptor (RXR) and is also activated by various lipophilic compounds produced by the body such as bile acids and steroids. PXR heterodimerized with RXR stimulates the transcription of cytochrome P450 3A monooxygenases (CYP3A) and other genes involved in the detoxification and elimination of the... 

Cytochromes P450 Are Monooxygenases Important for the Detoxification of Many Drugs for the Hydroxylation of Steroids... 

Iwahashi K, Kawai Y, Suwaki H, Hosokawa K, Ichikawa Y. 1993. A localization study of the cytochrome P-450(21)-linked monooxygenase system in adult rat brain. J Steroid Biochem Mol Biol 44 163-169. 

Most oxidation reactions are catalyzed by cytochrome P450 systems (see p. 318). These monooxygenases are induced by their substrates and show wide specificity. The substrate-specific enzymes of the steroid metabolism (see p. 376) are exceptions to this. 

Calcitriol (vitamin D hormone, lo,25-dihy-droxycholecalciferol) is a hormone closely related to the steroids that is involved in Ca homeostasis (see p. 342). In the kidney, it is formed from calcidiol by hydroxylation at C-1. The activity of calcidiol-1-monooxygenase [1] is enhanced by the hormone parathyrin (PTH). 

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. 

SALICYLATE 1-MONOOXYGENASE SARCOSINE OXIDASE STEROID HYDROXYLASES SULFITE OXIDASE SULEUR DIOXYGENASE THYMIDINE 2 -HYDROXYLASE TOLUENE DIOXYGENASE XANTHINE OXIDASE... 

In the rat, development to adult levels of activity takes about 30 days after which levels decline toward old age. In humans, however, hydroxylase activity increases up to the age of 6 years, reaching levels greater than those in the adult, which only decrease after sexual maturation. Thus the elimination of antipyrine and theophylline was found to be greater in children than in adults. It should be noted, however, that proportions of isoenzymes may be very different in neonates from the adult animal, and the development of the isoenzymes may be different. Thus, in the rat there seem to be four types of development for phase 1 metabolizing enzymes linear increase from birth to adulthood, type A (aniline 4-hydroxylation) low levels until weaning, then an increase to adult levels, type B (N-demethylation) rapid development after birth followed by rapid decline to low levels in adulthood, type C (hydroxylation of 4-methylcoumarin) and rapid increase after birth to a maximum and then decline to adult levels, type D. Patterns of development may be different between sexes as well as between species. For example, in the rat, steroid 16-a-hydroxylase activity toward androst-4-ene-3,17-dione develops in type B fashion in both males and females, but in females, activity starts to disappear at 30 days of age and is undetectable by 40 days. It seems that the monooxygenase system develops largely as a unit, with the rate dependent on species and sex of the animal and the particular substrate. 

FIGURE 21-37 Ring closure converts linear squalene to the condensed steroid nucleus. The first step in this sequence is catalyzed by a mixed-function oxidase (a monooxygenase), for which the cosubstrate is NADPH. The product is an epoxide, which in the next step is cyclized to the steroid nucleus. The final product of these reactions in animal cells is cholesterol in other organisms, slightly different sterols are produced, as shown. 

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