Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: DrugBank:EXPT00568 (ascorbate)
 23,072 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The selenoenzyme glutathione peroxidase in the presence of GSH effectively replaced catalase in the in vitro assay for gamma-butyrobetaine hydroxylase. Quantitatively, glutathione peroxidase was an order of magnitude more efficient than catalase, with maximal activity at less than 0.1 microM glutathione peroxidase in a standard reaction. Glutathione peroxidase prevented the loss of gamma-butyrobetaine hydroxylase during preliminary incubation with ferrous ions but without other substrates as well as in the course of the reaction. Regardless of whether glutathione peroxidase or catalase was present in the assay, the ascorbate concentrations needed to achieve half-maximal rates were similar (about 1 mM). Phosphate stimulated the rate of L-carnitine synthesis. Ferrous ion saturation indicated a pronounced effect of phosphate on the maximal velocity of the enzyme-catalyzed reaction, but its mechanism of action remains to be elucidated. Based on the subcellular distribution of gamma-butyrobetaine hydroxylase, catalase, and glutathione peroxidase, the role of glutathione peroxidase assumes importance. However, initial studies indicated that the assayable activity of liver gamma-butyrobetaine hydroxylase and L-carnitine concentrations in liver, blood plasma, and muscle were not significantly altered in selenium-deficient rats.
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PMID:gamma-Butyrobetaine hydroxylase and the protective role of glutathione peroxidase. 357 Dec 82

The possible role of superoxide anion in 2-oxoglutarate-coupled dioxygenase reactions has been investigated. gamma-Butyrobetaine hydroxylase (EC 1.14.11.1) was inhibited by human erythrocyte superoxide dismutase (EC 1.15.1.1), probably due to release of Cu(2+) or Zn(2+), as the inhibition was more pronounced after heat-inactivation of the dismutase and as Cu(2+) was a potent inhibitor. Bovine superoxide dismutase and the Mn(2+)-containing superoxide dismutase from Escherichia coli were not inhibitory. Superoxide anion generated from xanthine/xanthine oxidase was not stimulatory and could not replace ascorbate. Thymine 7-hydroxylase (EC 1.14.11.6) and thymidine 2'-hydroxylase (EC 1.14.11.3) were not inhibited by erythrocyte superoxide dismutase or stimulated by superoxide anion. gamma-Butyrobetaine hydroxylase was inhibited by a number of low-molecular-weight compounds, such as tetranitromethane, Nitro Blue Tetrazolium, adrenaline and Tiron, which may act as scavengers of superoxide anion. Involvement of this radical in other oxygenase reactions has been inferred from the findings that they were inhibitory for the respective enzymes. Several of these compounds also inhibited gamma-butyrobetaine hydroxylase. It could be concluded from these experiments, however, that mechanisms other than disposal of superoxide anion might equally well be operative, such as hydrophobic interaction with the enzyme protein and interaction with compounds required for full enzymic activity, e.g. iron and ascorbate. The results appear to rule out a requirement for superoxide anion generated in free solution, and have not yielded evidence for participation of enzyme-bound superoxide anion in 2-oxoglutarate-dependent hydroxylations.
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PMID:Does superoxide anion participate in 2-oxoglutarate-dependent hydroxylation? 629 7

The activity of gamma-butyrobetaine hydroxylase [4-trimethylaminobutyrate: oxygen oxidoreductase (3-hydroxylating), EC 1.14.11.1] was determined in different parts of a human kidney removed at surgery and in five perfused human cadaver kidneys. The activity in the 100,000 g supernatant fraction of a homogenate of whole kidneys was 48 nkat X g-1 protein (range 32-70 nkat X g-1protein). The cortex and outer medulla had four to six times higher activity than the inner medulla. A 60-fold purification from the soluble fraction of kidney homogenates with a 40% recovery was achieved by ammonium sulphate fractionation followed by DEAE-cellulose and hydroxylapatite chromatography. The enzyme had a specific activity of 2.4 mukat X g-1 protein but was contaminated to a minor degree by other proteins as judged by polyacrylamide gel electrophoresis. The Km values for gamma-butyrobetaine, 2-oxoglutarate and oxygen were 0.2 mmol/l, 0.3 mmol/l and 5.5% (by volume in the gas phase). There was an absolute requirement for ferrous ion. Half-maximal activity was reached with 10 mumol/l of Fe2+ in phosphate buffer (14 mmol/l) at pH 6.5. With a reaction time of 30 min ascorbate and catalase stimulated the reaction seven- and fivefold, respectively. Optimal pH value for the reaction was 6.2-6.5 in phosphate buffer. Decarboxylation of 2-oxoglutarate in the presence of 4-trimethylaminocrotonate or 4-dimethylaminobutyrate was 40 and 20%, respectively, of that with gamma-butyrobetaine as substrate. None of several compounds chemically related to 2-oxoglutarate, including oxaloacetate, stimulated gamma-butyrobetaine hydroxylation when tested in the absence of 2-oxoglutarate. We conclude that the requirements of the human kidney enzyme are similar to those previously reported for this enzyme from other sources.
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PMID:Gamma-butyrobetaine hydroxylase in human kidney. 715 61

gamma-Butyrobetaine hydroxylase catalyse the last step in carnitine biosynthesis, the formation of L-carnitine from gamma-butyrobetaine, a reaction dependent on Fe2+, alpha-ketoglutarate, ascorbate and oxygen. Initial attempts to purify the protein from rat liver showed that gamma-butyrobetaine hydroxylase is unstable. We, therefore, determined the influence of various compounds on the stability of gamma-butyrobetaine hydroxylase at different storage temperatures. The enzyme activity was best conserved by storing the protein at 4 degrees C in the presence of 200 g/l glycerol and 10 mM DTT. We subsequently purified the enzyme from rat liver to apparent homogeneity by liquid chromatography.
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PMID:Carnitine biosynthesis. Purification of gamma-butyrobetaine hydroxylase from rat liver. 1070 35