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We have been studying the transcriptional regulation of the rat P450c17 gene in both adrenocortical and Leydig cells, to assess which DNA sequences are required for its basal and hormonally stimulated transcription. Comparing the transcriptional regulation in both of these cell types enables us to demonstrate whether specific nuclear factors required for transcriptional regulation of the rat P450c17...
The rate of steroid synthesis is regulated by the rate of transport of cholesterol to mitochondria. The transport process involves two elements of the cytoskeleton (microfilaments and intermediate filaments) and Ca 2+ /calmodulin. Electron microscopy and immunofluorescence reveal that lipid droplets in which steroidogenic cholesterol is stored in the cytoplasm are tightly attached to...
Steroidogenesis begins with the metabolism of cholesterol to pregnenolone by the inner mitochondrial membrane cytochrome P450 side-chain cleavage (P450scc) enzyme. The rate of steroid formation, however, depends on the rate of cholesterol transport from intracellular stores to the inner mitochondrial membrane and loading of P450scc with cholesterol. In previous in vitro studies, we demonstrated...
3β-Hydroxysteroid dehydrogenase/Δ 5→4 -isomerase (3β-HSD) catalyzes the formation of Δ 4 -3-ketosteroids from Δ 5 -3β-hydroxysteroids, an obligate step in the biosynthesis not only of androgens and estrogens but also of mineralocorticoids and glucocorticoids. The enzyme is expressed in the adrenal cortex and in steroidogenic cells of the gonads, consistent with this...
The development of the rat adrenal gland during late gestational and neonatal stages was studied by following the expression of aldosterone synthase cytochrome P450 (P450aldo) and glucocorticoid-synthesizing cytochrome P450 (P45011β). Cells expressing P450aldo, a functional marker for the mineralocorticoid-synthesizing zona glomerulosa, were not detected until day 20 of fetal age, i.e., 2 days before...
The transcription of steroid hydroxylase genes is controlled by ACTH and cAMP in the adrenal cortex. In most instances the regulation appears to rely on transcription factors traditionally not associated with cAMP-dependent gene expression. For the non-traditional factors it remains necessary to elucidate the coupling of increases in intracellular cAMP and cAMP-dependent protein kinase (PKA) activity...
Meiotic maturation of fish oocytes is induced by the action of maturation-inducing hormone (MIH). 17α,20β-Dihydroxy-4-pregnen-3-one (17α,20β-DP) was identified as the MIH of several fish species, including salmonid fishes. The interaction of two ovarian follicle cell layers, the thecal and granulosa cell layers, is required for the synthesis of 17α,20β-DP; the thecal layer produces 17α-hydroxyprogesterone...
Aromatase (CYP19) mRNA is induced by follicle-stimulating hormone (FSH) in granulosa cells of preovulatory follicles and subsequently is rapidly diminished as a consequence of the luteinizing hormone (LH) surge. Primary cultures of rat granulosa cells were used to identify some of the cellular mechanisms by which FSH increases and LH decreases steady-state levels of aromatase mRNA. Induction of...
Steroidogenic acute regulatory protein (StAR) plays a critical role in regulating the rate-limiting step in steroid hormone synthesis, cholesterol side-chain cleavage. StAR gene expression is transcriptionally controlled in the gonads by gonadotropic hormones via a cAMP second message. We have begun to analyze factors responsible for the transcriptional activation of the StAR gene. The human StAR...
The 2.9-kb mRNA of 17β-hydroxysteroid dehydrogenase IV codes for an 80-kDa (737 amino acids) protein featuring domains that are not present in the other human 17β-hydroxysteroid dehydrogenases. The N-terminal part reveals conserved motifs of the short-chain alcohol dehydrogenase family. The central- and C-terminal domains are similar to peroxisomal enzymes for β-oxidation of fatty acids and to sterol...
Mitochondrial monooxygenase systems are involved in the biosynthesis of glucocorticoids, mineralocorticoids, bile acids, and 1,25-dihydroxyvitamin D. The reactions are catalyzed by specific P450 enzymes that receive reducing equivalents via NADPH-ferredoxin oxidoreductase (adrenodoxin reductase) and ferredoxin (adrenodoxin). Although the three-dimensional structures of the individual components...
The first step in the synthesis of all steroids is the cleavage of cholesterol side chain, catalyzed by an electron transport system located in mitochondria consisting of ferredoxin reductase, ferredoxin, and cytochrome P450scc. These proteins are present in adrenal, gonad, placenta, and some parts of the brain. In addition, ferredoxin and ferredoxin reductase are also found in the kidney and liver...
Studies of the regulation of androgen synthesis in steroidogenic cells have focused on both transcriptional and post-translational regulation of the proteins that catalyze these reactions: the P450c17 that catalyzes the production of DHEA or androstenedione in consecutive hydroxylase and lyase activities, and the 17β-hydroxysteroid dehydrogenase (17β-HSD) that catalyzes the conversion of androstenedione...
Over 400 P450s have been identified to date in prokaryotes and eukaryotes, plants and animals, mitochondria and endoplasmic reticulum. These enzymes function in areas such as xenobiotic metabolism and steroidogenesis. The eukaryotic members of this gene superfamily of proteins have proved difficult to study because of the hydrophobic nature of their substrates, their various redox partners, and...
17β-Hydroxysteroid dehydrogenase (17β-HSD) controls the last step in the formation of all androgens and all estrogens. This crucial role of 17β-HSD is performed by at least five 17β-HSD isoenzymes having individual cell-specific expression, substrate specificity, regulation mechanisms, and reductive or oxidative catalytic activity. Both estrogenic and androgenic 17β-HSD activities were found in...
The syndrome of apparent mineralocorticoid excess (AME) is an inherited form of hypertension in which 11β-hydroxysteroid dehydrogenase (11-HSD) is defective. This enzyme converts cortisol to its inactive metabolite, cortisone. The deficiency allows mineralocorticoid receptors to be occupied by cortisol, because these receptors themselves have similar affinities for cortisol and aldosterone. There...
The type 1 and type 2 isoforms of human 11β-hydroxysteroid dehydrogenase (11β-HSD) play a crucial role, respectively, in modulating glucocorticoid and mineralocorticoid hormone action. Deficiency of the 11β-HSD2 isoform, as described in the syndrome of apparent mineralocorticoid excess and following liquorice (glycyrrhetinic acid) or carbenoxolone ingestion, results in hypertension in which cortisol...
17β-Hydroxysteroid dehydrogenases (17β-HSDs) are enzymes involved in both the activation and inactivation of androgens and estrogens. 17β-HSD type 1 shows a high specificity for C 18 steroids and is the major isozyme in the granulosa cells of the ovary. Its role is to convert the inactive C 18 steroid estrone to the active estrogen estradiol, which in turn locally promotes...
Much of our understanding of P450 reaction mechanisms derives from studies on P450cam, a bacterial camphor hydroxylase. P450cam has served as the model for understanding detailed structure/function relationships in mammalian P450 enzymes, which have not proved amenable to x-ray crystallographic techniques. To expand and improve the P450 model, we solved the structure of P450eryF, a cytochrome P450...
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