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At least 1,009 records · Page 56Linked to original sources
PubMed1982

The mechanism of alpha-ketoisocaproate oxygenase. Formation of beta-hydroxyisovalerate from alpha-ketoisocaproate.

A soluble alpha-ketoisocaproate oxygenase from rat liver catalyzes the decarboxylation and hydroxylation of alpha-ketoisocaproate to form beta-hydroxyisovalerate. The source of oxygen (O2 or H2O) enzymatically incorporated into beta-hydroxyisovalerate was investigated using 18O2 and H218O. Greater than 92% of the carboxyl groups of beta-hydroxyisovaleric acid contained 1 18O atom from 18O2 and 15% of the beta-hydroxyl oxygens of beta-hydroxyisovaleric acid contained 18O from 18O2. Since some oxygen of the beta-hydroxyl group is derived from O2 and since others have shown a rapid H2O in equilibrium ROH exchange for similar reactions, we conclude that both of the oxygens of beta-hydroxyisovaleric acid are derived from O2 and that exchange of water oxygen with the beta-hydroxyl group of beta-hydroxyisovaleric acid must occur with an intermediate of the reaction. Thus, the alpha-ketoisocaproate oxygenase would be a dioxygenase. A mechanism consistent with the 18O experiments and other properties of the enzyme is proposed.

Animals↗
PubMed1980

Purification and characterization of an oxygenase component in benzoate 1,2-dioxygenase system from Pseudomonas arvilla C-1.

The benzoate 1,2-dioxygenase system of Pseudomonas arvilla consists of two proteins, an NADH-cytochrome c reductase and an oxygenase. The oxygenase component was purified to apparent homogeneity by the criteria of polyacrylamide gel electrophoresis from benzoate-induced cells of P. arvilla. The molecular weight of the enzyme was determined to be 273,000 by sedimentation equilibrium analysis, 280,000 by electrophoresis on polyacrylamide gels of different concentrations, and 270,000 by Sepharose CL-6B gel filtration, respectively. The sedimentation coefficient, the Stokes radius, and the partial specific volume of the enzyme were calculated to be 10.0 S, 56 A, and 0.72 ml/g, respectively. The isoelectric point of the enzyme was estimated to be pH 4.5. The enzyme contained about 10 mol of iron and about 8 mol of labile sulfide/mol of enzyme. The iron-sulfur clusters of the enzyme were suggested to be (2Fe-2S*) from cluster-extrusion experiments (S*, sulfide, acid-labile sulfur). No significant amounts of heme or flavin were detected in the enzyme. The enzyme exhibited absorption spectrum with maxima at 279, 325, and 464 nm. The turnover number of the enzyme in the presence of saturating amounts of NADH-cytochrome c reductase, the other component of the benzoate 1,2-dioxygenase system, was calculated to be 22,000 at 24 degrees C. The apparent Km values for the reductase, benzoate, and molecular oxygen were 26 (0.97 mg of protein/ml), 3.9, and 4.3 microM, respectively.

Amino Acids↗
PubMed1994

Induction of heart heme oxygenase-1 (HSP32) by hyperthermia: possible role in stress-mediated elevation of cyclic 3':5'-guanosine monophosphate.

Presently we have investigated the carbon monoxide generating capacity of the cardiovascular system under normal and stress conditions by examining the microsomal heme oxygenase system at the transcript, protein and activity levels; and have assessed response of heart nitric oxide (NO) synthase activity and cyclic GMP levels to stress. Heme oxygenase (HO) isozymes, HO-1 (HSP32) and HO-2, catalyze the rate limiting step in the only known pathway in eukaryotes for the generation of the potential cellular message, carbon monoxide, and the antioxidant, bilirubin. We show expression of HO-1 and HO-2 at both the transcription and protein levels under normal conditions in the heart and descending aorta, and demonstrate the sensitivity of only the HO-1 isozyme to heat stress in these tissues. The ratio of the two HO-2 homologous transcripts (approximately 1.9 and 1.3 Kb) present in the atrium, ventricles and descending aorta and their levels were not altered by hyperthermia (42 degrees C, 20 min) when measured 1 or 6 hr after treatment. In contrast, hyperthermia caused a rapid, robust and coordinate increase of approximately 10- to 32-fold in the approximately 1.8-Kb HO-1 mRNA in these tissues when measured 1-hr post-treatment. Hyperthermia also caused a significant increase in both HO-1 protein and heme degradation capacity in the heart. Furthermore, the induction of HO-1 protein in the heart was accompanied by a significant elevation in tissue cyclic GMP level first detected 1-hr post-treatment and was sustained 6 hr after heat shock.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Oxidoreductases↗
PubMed1993

Singlet oxygen: a primary effector in the ultraviolet A/near-visible light induction of the human heme oxygenase gene.

Both singlet oxygen and the hydroxyl radical are generated in mammalian cells by UVA (320-380 nm) and possibly near-visible (380-420 nm) radiation. We have modulated the cellular levels of these two reactive oxygen species in order to compare their involvement in the induction of the human heme oxygenase (HO) gene by broad spectrum UVA/near-visible light (UVA/NVL). Irradiation in deuterium oxide (in which singlet oxygen has a longer half-life) enhances the broad spectrum UVA/NVL induction of this gene. Sodium azide and L-histidine which are scavengers of both singlet oxygen and the hydroxyl radical reduce the fluence-dependent accumulation of HO mRNA, while compounds which are only hydroxyl radical scavengers, namely, mannitol and dimethyl sulfoxide do not. Rose Bengal, a known generator of singlet oxygen, also increases the HO mRNA levels, and this induction is enhanced in deuterium oxide. We conclude that the observed effects of deuterium oxide and singlet oxygen scavengers on HO mRNA levels are not due to a nonspecific effect on transcription but that singlet oxygen is a primary effector in the UVA/NVL induction of the human heme oxygenase gene.

Azides↗
PubMed1994

Interaction of Fe-protoporphyrin IX and heme analogues with purified recombinant heme oxygenase-2, the constitutive isozyme of the brain and testes.

Heme oxygenase-2 (HO-2) is the predominant form of heme oxygenase in the brain and testes. The enzyme is not readily amenable to isolation from mammalian tissues and has not been characterized for its kinetic properties and interaction with metalloporphyrins. Presently a rat HO-2 cDNA (Rotenberg, M.O., and Maines, M. D. (1990) J. Biol. Chem. 265, 7501-7506) was used to generate a construct with a neutral hydrophobicity profile at its COOH terminus for expression of nearly full-length HO-2 protein in Escherichia coli. The procedures used for HO-1 were of no utility in purification of HO-2. A multistep protocol developed for isolation of HO-2 resulted in a homogeneous protein with a specific activity up to 6,500 nmol of bilirubin/mg/h. Based on SDS-polyacrylamide gel electrophoresis and Western blot analyses, the protein had an apparent molecular mass of approximately 34 kDa. HO-2 binds Fe-protoporphyrin (heme) at near molar unity to give a complex with the absorption maximum at 403 nm. The Soret band has a blue shift to 430 nm when heme iron is reduced, with distinct alpha and beta bands at 485 and 550 nm, respectively. The Soret band of the CO complex of ferrous heme.HO-2 is at 420 nm, and alpha and beta bands are at 540 and 572 nm, respectively. The apparent Km for Fe-protoporphyrin is 0.33 microM, with a Vmax of 0.45 nmol of bilirubin/mg/h. Zn-protoporphyrin is a strong mixed inhibitor of enzyme activity, whereas Co-protoporphyrin is a poor competitive inhibitor of activity. When HO-2 was preincubated (10 min at 4 degrees C) with Fe-protoporphyrin, the cobalt complex did not inhibit enzyme activity, whereas the Zn-protoporphyrin effectively inhibited activity. Calorimetric measurements suggest that HO-2/heme interaction involves one type of association producing a single heat absorption peak upon melting of the complex and that the unfolding is not reversible. The association increases the enthalpy of HO-2 (130 kcal/mol versus 184 kcal/mol) and increases the stability to heat denaturation by 9 degrees C. Heat duration of zinc complex involves at least two stages of unfolding.

Amino Acid Sequence↗
PubMed1993

Prolonged clinical use of a heme oxygenase inhibitor: hematological evidence for an inducible but reversible iron-deficiency state.

The heme oxygenase inhibitor tin (Sn4+)-mesoporphyrin, administered to two 17-year-old Crigler-Najjar type I patients during a 400-day study to lower plasma bilirubin levels, also produced changes, beginning approximately 50 days after initiation of treatment, in hematological and iron metabolism indices consistent with the development of iron deficiency anemia. These indices were responsive to iron supplementation and reverted to normal after termination of inhibitor treatment. Tin-mesoporphyrin enhances biliary heme excretion and inhibits intestinal heme oxygenase when administered orally or parenterally; the changes in blood indices could thus reflect, in part, blockade of heme catabolism and therefore of uptake of heme-derived iron, by intestinal epithelium. This action of the inhibitor suggests that such agents may facilitate studies involving aberrant metabolism of heme-derived iron in humans and that they merit further investigation with respect to their potential value in enhancing iron disposal in certain disorders such as those related, for example, to transfusion-induced iron overload states.

Adolescent↗
PubMed1993

[Nuclear proteins, specifically binding the regulatory region of rat tryptophan oxygenase].

Using electrophoretic mobility shift assay we have analysed the binding of rat liver nuclear proteins to the fragments from -466 to -292 and from -292 to -178 relative to the transcriptional start site of the rat tryptophan oxygenase gene. Studies of the competition with a synthetic consensus sequence for the NF 1 recognition site have shown that the liver nuclear proteins, responsible for the formation of specific complexes with these fragments belong to the family of the nuclear factor 1 (NF 1). We have also found that the trans-acting factors of the NF 1 family form several complexes with each of the two tested fragments of the tryptophan oxygenase gene.

Animals↗
PubMed1993

Enhancement of heme oxygenase expression and activity in A431 squamous carcinoma multicellular tumor spheroids.

We have investigated the effects of the growth of A431 human squamous carcinoma cells as three-dimensional aggregates (multicellular tumor spheroids) on the expression and enzyme activity of heme oxygenase (HO). We demonstrate that A431 squamous carcinoma cells grown as day 4 spheroids selectively increase the expression of heme oxygenase 1 (HO-1), caused, directly or indirectly, by three-dimensional cell-cell contact effects. Steady-state levels of both mRNA and protein are significantly enhanced in spheroids compared with day 4 monolayers (approximately 13-fold). Because of the similarity of apparent half-lives between monolayers (2.7 h) and spheroids (2.1 h), it appears that the increases are caused at least partly by altered transcriptional rates. Total HO enzyme activity, measured by carbon monoxide production, is also up-regulated (2.6-fold) in spheroids, compared to that in monolayers. This increase indicates that the up-regulation in HO-1 protein expression corresponds to an increase in functional enzyme levels. We propose that HO may play a more complex role in cellular metabolism than would be evident from studies using two-dimensional monolayer cultures.

Blotting, Northern↗
PubMed1996

Arsenite, but not cadmium, induces ornithine decarboxylase and heme oxygenase activity in rat liver: relevance to arsenic carcinogenesis.

Sodium arsenite and cadmium chloride, were administered orally to adult female rats at 21 and 4 h prior to sacrifice. Liver, lung, skin and urinary bladder were the tissues studied. DNA damage, cytochrome P450, glutathione content (GSH), ornithine decarboxylase (ODC), serum alanine aminotransferase and heme oxygenase activity were measured. Sodium arsenite increased rat hepatic ODC activity at 1.6 and 24.6 mg/kg and hepatic heme oxygenase activity at 8.2 and 24.6 mg/kg, but did not cause any DNA damage. Cadmium chloride did not affect any of the six parameters tested. These findings suggest that sodium arsenite may be a promoter rather than an initiator of carcinogenesis.

Alanine Transaminase↗
PubMed1995

Parallel induction of heme oxygenase-1 and chemoprotective phase 2 enzymes by electrophiles and antioxidants: regulation by upstream antioxidant-responsive elements (ARE).

BACKGROUND: Heme oxygenase (HO; EC 1.14.99.3) catalyzes the conversion of heme to biliverdin, which is reduced enzymatically to bilirubin. Since bilirubin is a potent antioxidant and heme a pro-oxidant, HO may protect cells against oxidative damage. HO-1 is highly inducible by diverse chemical agents, resembling those evoking induction of phase 2 enzymes (i.e., Michael reaction acceptors, heavy metals, trivalent arsenicals, and sulfhydryl reagents). Phase 2 enzymes (glutathione transferases; NAD (P)H:quinone reductase; glucuronosyltransferases) are regulated by antioxidant-responsive elements (ARE), and their induction protects against chemical carcinogenesis. Is HO-1 regulated by chemical agents and enhancer elements similar to those controlling phase 2 enzymes? MATERIALS AND METHODS: Induction of HO-1 by phorbol ester and heavy metals is transcriptionally controlled through a 268-bp SX2 fragment, containing two phorbol ester-responsive (TRE) sites (TGAC/GT C/AA) which overlap ARE consensus sequences (TGACNNNGC). Therefore, mutations of the SX2 element designed to distinguish ARE from TRE were inserted into chloramphenicol acetyltransferase (CAT) reporter plasmids, and the response of the CAT activity of murine hepatoma cells stably transfected with these constructs was examined with a wide range of inducers of phase 2 enzymes. RESULTS: All compounds raised HO-1 mRNA and CAT expression constructs containing wild-type SX2. When the SX2 region was mutated to alter TRE consensus sequences without destroying the ARE consensus, full inducibility was preserved. Conversely, when the ARE consensus was disturbed, inducibility was abolished. CONCLUSION: Induction of heme oxygenase-1 is regulated by several chemically distinct classes of inducers (mostly electrophiles), which also induce phase 2 enzymes, and these inductions are mediated by similar AREs. These findings support the importance of HO-1 as a protector against oxidative damage and suggest that HO-1 induction is part of a more generalized protective cellular response that involves phase 2 enzymes.

Antioxidants↗
PubMed1977

Glucocorticoid control of the development of tryptophan oxygenase in the young rat.

Tryptophan oxygenase activity follows a characteristic developmental pattern in the young rat, being absent until about 2 weeks of life, then attaining adult levels by the 3rd week. We have investigated the factors which control this process and determined that the increase in enzymatic activity results from increased glucocorticoid release between the 14th and 21st days. This conclusion was based on our observation that adrenalectomy completely arrests the development of the enzymatic activity. Twenty-one-day-old animals which were adrenalectomized on the 10th day, and thus possess no demonstrable enzymatic activity, could respond to cortisol treatment with an elevation of tryptophan oxygenase activity. Administration of either cycloheximide or actinomycin D completely inhibited this response, suggesting that both protein synthesis and RNA synthesis were requisite for the development of the enzyme. Immunochemical studies revealed that the enzyme found in the young animal was identical with that extracted from the adult rat; furthermore, the increase in activity observed in the developing rat is the result of increased enzyme protein levels. Direct measurement of the synthetic and degradative rates showed the accumulation of enzyme protein to depend upon increased synthetic activity, and not upon decreased enzyme degradation.

Adrenal Glands↗
PubMed1996

Heme oxygenase inhibitor zinc protoporphyrin IX causes an activation of nitric oxide synthase in the rabbit internal anal sphincter.

The studies were performed in the rabbit internal anal sphincter (IAS) smooth muscle strips to examine the influence of the heme oxygenase inhibitor, [zinc protporphyrin (ZnPP IX)], on basal tone. ZnPP IX produced a concentration-dependent fall in the basal tone and was the focus of our investigation. To examine the mechanism of the fall in IAS tone by ZnPP IX, the effect of different concentrations of ZnPP IX on basal IAS tone and the release of nitric oxide were examined before and after the neurotoxin tetrodotoxin and various nitric oxide synthase (NOS) inhibitors. The inhibitory effect of ZnPP IX was blocked by the NOS inhibitors L-NG-nitroarginine, NG-monomethyl-L- arginine and L-N5-(1-iminoethyl)ornithine and the neurotoxin TTX. The fall in IAS tension by ZnPP IX was accompanied by a release of NO. ZnPP IX(1 x 10(-3)M) caused a fall in IAS tension of 43.7% which was reduced to 16.5% in the presence of L-NG-nitroarginine (1 x 10(-4)M). Furthermore, the fall in IAS tone in the presence of ZnPP IX was restored both by the NOS inhibitors and tetrodotoxin. The basal release of nitric oxide in these experiments was 0.50 +/- 0.07 nmol and in the presence of ZnPP IX (1 x 10(-3)M), it increased to 1.72 +/- 0.28 nmol (more than a 3-fold increase). Thus the fall in the basal IAS tone by ZnPP IX was associated with a release of NO from the myenteric neurons as these effects were significantly blocked by the NOS inhibitors and tetrodotoxin. We conclude that in the rabbit IAS, ZnPP IX causes a fall in the basal IAS tension by the activation of NOS in myenteric neurons. We speculate that in the resting state, the heme oxygenase pathway exerts important counter-regulatory effects on the NOS pathway and when blocked (e.g., by ZnPP IX), the underlying NOS pathway is unmasked leading to a massive and prolonged release of NO. The exact significance of this mechanism remains to be determined.

Anal Canal↗
PubMed1996

Reductase and oxygenase activities of semisynthetic flavocytochromes based on cytochrome P450 2B4.

A synthetic flavocytochrome with the reductase and oxygenase activities was obtained by covalent binding of riboflavin to cytochrome P450 2B4. The reactions catalyzed by the newly synthesized flavocytochromes were studied. Formation of carboxycomplex with the reduced form of hemoprotein led to 60-80% inhibition of oxygenase reactions indicating the leading role of reduced heme iron in generating active oxygen species by flavocytochromes.

Aniline Compounds↗
PubMed1983

Familial and constitutional bleeding disorder due to platelet cyclo-oxygenase deficiency.

Three family members from two successive generations had a bleeding tendency. Their template bleeding time was prolonged and platelet aggregation induced by ADP and adrenaline showed no second wave; collagen at low to moderate concentrations failed to aggregate and release ATP, whereas higher amounts aggregated and released. Aggregation and release due to thrombin, ristocetin, and synthetic epoxy derivatives (U 44069 and U 46619) were normal. Arachidonate (AA) was inactive, and was not converted either in thromboxane (TX) A2 activity evaluated on the rabbit aorta strip, nor in TXB2 evaluated by radioimmunoassay and by radiochromatography. The parallel impairment of TXB2 and PGE2 formation by the patient's platelets are compatible with a platelet cyclo-oxygenase deficiency. This study suggests that transmission is autosomal dominant, and confirms that cyclo-oxygenase is not needed for aggregation and ATP release by high amounts of collagen.

Adolescent↗
PubMed1986

Combined effect of ethanol and carbon disulphide on cytochrome P-450 mono-oxygenase, lipid peroxidation and ultrastructure of the liver in chronically exposed rats.

A 5-month treatment of rats with ethanol (10% solution in drinking water) stimulated aniline p-hydroxylase and the microsomal ethanol oxidizing system (MEOS) by 140 and 70%, respectively, cytochrome P-450 by 22% and accompanied by lipid peroxidation by 40% in microsomes. It also caused smooth endoplasmic reticulum (SER) proliferation and rough endoplasmic reticulum (RER) degranulation in hepatocytes. Repeated inhalatory exposure of rats to 1.5 g/m3 of CS2, 5 h daily, 5 days a week for 5 months decreased aniline p-hydroxylase and MEOS by 70 and 55% respectively, doubled hexobarbital sleeping time and depressed cytochrome P-450 by 30% and its conversion to cytochrome P-420; these effects were accompanied by the appearance of cytochrome P-420, the intensification of lipid peroxidation in microsomes and some degranulation of RER in hepatocytes. Combined exposure of rats to ethanol and CS2 resulted in a significant potentiation of the inhibitory effects of CS2 on cytochrome P-450 mono-oxygenase and MEOS but with enhancement of CS2 effects on the liver microsomal mono-oxygenase, but CS2 decreased the effect of ethanol on SER proliferation. The interaction both on the biochemical and the morphological level can be explained with the ethanol-stimulated biotransformation of CS2 to reactive electrophilic derivative(s), the subsequent destruction of cytochrome P-450 to cytochrome P-420 and the intensification of lipid peroxidation.

Animals↗
PubMed2007

Inhibitory effect of Panax notoginseng on nitric oxide synthase, cyclo-oxygenase-2 and neutrophil functions.

A water extract of Panax notoginseng Buck F.H. Chen. (Arialiaceae) root (PN) is being used as a therapeutic agent to stop haemorrhages and as a tonic to promote health in Korean and Chinese medicine. The pharmacokinetic profiles of PN have not been accurately investigated. The preliminary aim was to elucidate the pharmacokinetic features of PN. First, the prevention of neutrophil functions was assessed. PN inhibited neutrophil functions, including degranulation, superoxide generation and leukotriene B4 production, without any effect on 5-lipoxygenase activity. PN reduced nitric oxide (NO) and prostaglandin (PG)E2 production in mouse peritoneal macrophages stimulated with lipopolysaccharide (LPS) while no influence on the activity of inducible NO synthase (iNOS), cyclo-oxygenase-2 (COX-2) or cyclo-oxygenase-1 (COX-1) was observed. PN significantly reduced mouse paw oedema induced by carrageenan. The results indicate that PN exerts antiinflammatory effects related to the inhibition of neutrophil functions and NO and PGE2 production, which could be due to a decreased expression of iNOS and COX-2.

Animals↗
PubMed1996

Effects of cyclo-oxygenase inhibition on ozone-induced respiratory inflammation and lung function changes.

Inhalation of O3 causes airways neutrophilic inflammation accompanied by other changes including increased levels of cyclo-oxygenase products of arachidonic acid in bronchoalveolar lavage fluid (BALF). Ozone O3 exposure also causes decreased forced vital capacity (FVC) and forced expiratory volume after 1 s (FEV(1)), associated with cough and substernal pain on inspiration, and small increases in specific airway resistance (SRAW). The spirometric decrements are substantially blunted by pretreatment with indomethacin. Since the O3-induced decrement in FVC is due to involuntary inhibition of inspiration, a role for stimulation of nociceptive respiratory tract afferents has been suggested and cyclo-oxygenase products have been hypothesized to mediate this stimulation. However, the relation (if any) between the O3-induced neutrophilic airways inflammation and decreased inspiratory capacity remains unclear. We studied the effects of pharmacologic inhibition of O3-induced spirometric changes on the inflammatory changes. Each of ten healthy men was exposed twice (5-week interval) to 0.4 ppm O3 for 2 h, including 1 h of intermittent exercise (ventilation 601*min(-1)). One-and-a-half hours prior to and midway during each exposure the subject ingested 800 mg and 200 mg, respectively, of the non-steroidal anti-inflammatory drug ibuprofen (IBU), or placebo [PLA (sucrose)], in randomized, double-blind fashion. Spirometry and body plethysmography were performed prior to drug administration, and before and after O3 exposure. Immediately following postexposure testing, fiberoptic bronchoscopy with bronchoalveolar lavage (BAL) was performed. Neither IBU nor PLA administration changed pre-exposure lung function. O3 exposure (with PLA) caused a significant 17 percent mean decrement in FEV(1) (P <0.01) and a 56 percent increase in mean SRAW. Following IBU pretreatment, O3 exposure induced a significantly lesser mean decrement in FEV(1) (7 percent) but still a 50 percent increase in mean SRAW. IBU pretreatment significantly decreased post-O3 BAL levels of prostaglandin E2 (PGE2) by 60.4 percent (P <0.05) and thromboxane B(2) (TxB(2)) by 25.5 percent (P <0.05). Of the proteins, only interleukin-6 was significantly reduced (45 percent, P <0.05) by IBU as compared to PLA pretreatment. As expected, O3 exposure produced neutrophilia in BALF. There was, however, no effect of IBU on this finding. None of the major cell types in the BALF differed significantly between pretreatments. We found no association between post-exposure changes of BALF components and pulmonary function decrements. We conclude that IBU causes significant inhibition of O3-induced increases in respiratory tract PGE(2) and TxB(2) levels concomitant with a blunting of the spirometric response. This is consistent with the hypothesis that the products of AA metabolism mediate inhibition of inspiration. However, IBU did not alter the modest SRAW response to O3.

Adult↗
PubMed1983

Stimulation of cyclo-oxygenase by lidocaine, a pro-lipoperoxidant.

Lidocaine, which was recently demonstrated to be a good pro-lipoperoxidant, was tested on in vitro PGs biosynthesis, and on arachidonate-induced arterial hypotension, in the rabbit. In the in vitro experiments, lidocaine alone was a poor stimulant of cyclo-oxygenase, but it enhanced significantly the cyclo-oxygenase activation of uric acid. In the rabbit, lidocaine lowered the i.v. arachidonate dose necessary to obtain a significant drop of blood pressure.

Animals↗