Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.6.99.3 (diaphorase)
 5,903 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Pituitary-determined hormones regulate the expression of hepatic cytochromes P-450 through processes involving both negative and positive controls. Accordingly, protein levels of several P-450 forms are elevated in rat liver following hypophysectomy [P-450 forms designated 2a (gene IIIA2), RLM2 (gene IIA2), and PB-4 (gene IIB1)], whereas protein levels of others are suppressed [e.g., P-450 2c (gene IIC11)]. In the present study, microsomal steroid hydroxylase activities associated with these same P-450 forms were found to be decreased by hypophysectomy, despite elevations in protein levels for several of them. Studies were, therefore, undertaken to determine the biochemical basis for this decrease in microsomal P-450 enzyme specific activity. In vivo treatment of hypophysectomized rats with gonadotropin, under conditions that restore heme to testis P-450, and heme reconstitution experiments carried out with liver homogenates indicated that a deficiency in P-450-associated heme is unlikely to account for the observed decreases in liver P-450 enzyme specific activity. Analysis of the flavoprotein P-450 reductase, however, revealed that the reductase protein and its associated cytochrome c reductase activity are decreased by 50 to 75% in liver microsomes isolated from hypophysectomized rats. Moreover, supplementation of isolated liver microsomes with exogenous purified P-450 reductase stimulated microsomal steroid hydroxylase activity preferentially in the hypophysectomized rats, to levels consistent with the observed changes in P-450 protein levels. Thus, a deficiency in P-450 reductase, which is a rate-limiting component for many P-450-dependent hydroxylation reactions, appears to be responsible for the decrease in steroid hydroxylase specific activity in the hypophysectomized rats. Although growth hormone, adrenocorticotropic hormone, and chorionic gonadotropin were each ineffective at restoring hepatic P-450 reductase when administered to hypophysectomized rats, substantial restoration of P-450 reductase levels could be achieved by treatment of the hypophysectomized rats with thyroxine. Thyroxine treatment of these rats also elevated the microsomal steroid hydroxylase activities associated with the individual hepatic P-450 forms to levels commensurate with their respective P-450 protein levels. These results establish that hepatic P-450 reductase is subject to hormonal controls that are distinct from those governing cytochrome P-450 expression and further demonstrate the complexity of endocrine control of hepatic steroid hormone metabolism.
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PMID:Hypophysectomy differentially alters P-450 protein levels and enzyme activities in rat liver: pituitary control of hepatic NADPH cytochrome P-450 reductase. 249 35

EPR spectroscopy was used to investigate the cytochrome P-450-dependent steroid hydroxylase ecdysone 20-mono-oxygenase of the cotton leafworm (Spodoptera littoralis) and the redox centres associated with membranes from the fat-body mitochondrial fraction. Intense features at g = 2.42, 2.25 and 1.92 from oxidized mitochondrial membranes have been assigned to the low-spin haem form of ferricytochrome P-450, probably of ecdysone 20-mono-oxygenase. High-spin cytochrome P-450 (substrate-bound) was tentatively assigned to a signal at g = 8.0, which was detectable from membranes as prepared. An EPR signal characteristic of a [2Fe-2S] cluster detected from the soluble mitochondrial matrix fraction has been shown to be distinct from the signals associated with mitochondrial NADH dehydrogenase and succinate dehydrogenase, and has therefore been attributed to a ferredoxin. We conclude that the S. littoralis fat-body mitochondrial electron-transport system involved in steroid 20-hydroxylation comprises both ferredoxin and cytochrome P-450 components, and thus resembles the enzyme systems of adrenocortical mitochondria. EPR signals characteristic of the respiratory chain were also observed from fat-body mitochondria and assigned to the iron-sulphur clusters associated with Complex I (Centres N1, N2), Complex II (Centres S1, S3), Complex III (the Rieske centre), and the copper centre of Complex IV, demonstrating similarities to mammalian mitochondria. The reduced membrane fraction also yielded a major resonance at g = 2.09 and 1.88 characteristic of the [4Fe-4S] cluster of electron-transferring flavoprotein: ubiquinone oxidoreductase. As the fat-body is the major metabolic organ of insects, this protein is presumably required for the beta-oxidation of fatty acids in mitochondria. High-spin haem signals in the low-field region of spectra also demonstrated that the mitochondrial fraction contains relatively high concentrations of catalase.
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PMID:EPR spectroscopic characterization of the iron-sulphur proteins and cytochrome P-450 in mitochondria from the insect Spodoptera littoralis (cotton leafworm). 774 2