Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:Q8NEX9 (reductase)
 26,410 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The ability of synthetic metalloporphyrins to suppress heme oxygenase activity and bilirubin formation has recently become of considerable clinical and experimental interest for suppression of jaundice in humans, including neonatal hyperbilirubinemia. The present investigation compares the biochemical effects of Sn- and Zn-protoporphyrins on the predominant heme oxygenase isozyme present in the brain (HO-2) at activity, protein, and transcript levels and describes the ability of Sn-protoporphyrin to adversely affect this isozyme. Specifically, 6 h after a modest dose (50 mumol/kg, i.v.) of Sn-protoporphyrin, heme oxygenase activity in rat brain was nearly undetectable. In addition, as revealed by Western blot analysis, HO-2 protein level was decreased by 20% and the electrophoretic behavior of the protein in the microsomal membranes was altered. Moreover, the activity of NADPH-cytochrome P-450 reductase, which is required for the oxidation of heme molecule, was markedly decreased (60% of control). Western immunoblot analysis revealed also a pronounced decrease in the reductase protein level. The inducible form of heme oxygenase, HO-1, was not detectable by immunoblotting in brain microsomes of either control or Sn-protoporphyrin-treated animals. Northern blot analyses did not reveal decreases in the levels of the single HO-1 mRNA (1.8 kb) or the two HO-2 transcripts (1.3 and 1.9 kb), suggesting that Sn-protoporphyrin mediates its effects on heme oxygenase isozymes at the protein level. Zn-protoporphyrin, on the other hand, had no deleterious effect on brain parameters presently investigated.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Tin-protoporphyrin-mediated disruption in vivo of heme oxygenase-2 protein integrity and activity in rat brain. 140 70

The present report describes, for the first time, the identification of two constitutive forms of heme oxygenase, designated as HO-1 and HO-2, in rat liver microsomal fractions. HO-1 was purified to homogeneity and exhibited a specific activity of up to 4000 nmol of bilirubin/mg of protein/h. HO-2 was partially purified to a specific activity of 250 nmol of bilirubin/mg of protein/h. In the native state, the relative activity of HO-2 surpassed that of HO-1 by 2-3-fold. However, a remarkable difference existed in the regulatory mechanism(s) for the production of the two enzyme forms. Whereas the activity of HO-1 was increased up to 100-fold in response to cobalt, cadmium, hematin, phenylhydrazine, and bromobenzene, that of HO-2 was fully refractory to these agents. The two forms differed in their apparent Km, thermolability, ammonium sulfate precipitation, antigenicity, electrophoretic mobility under nondenaturing conditions, and chromatographic behavior. Specifically, for HO-1 the apparent Km value was 0.24 microM, whereas that for HO-2 was 0.67 microM. HO-2 preparation was more susceptible to heat inactivation; nearly 65% activity was retained by HO-1 preparation after exposure to 60 degrees C for 10 min, whereas under the same conditions only about 25% of HO-2 activity was retained. When subjected to ammonium sulfate precipitation the bulk of HO-1 activity precipitated between 0 and 35% saturation, whereas that of HO-2 was precipitated between 35 and 65% saturation. The two forms appeared as immunologically different entities, in so far as a crossreactivity between antibody raised against HO-1 in rabbit and HO-2 could not be detected. Similarities were observed in respect to cofactor requirements for activity, sensitivity to inhibitors, as well as their reactivity towards the substrates used in this study, i.e. hematin, hematoheme, and cytochrome c. Specifically both forms of the enzyme required NADPH-cytochrome c (P-450) reductase, NADPH or NADH, and O2 for activity, and reactions were inhibited by KCN, NaN3, and CO. Both forms cleaved the tetrapyrrole molecule exclusively at the alpha-meso bridge to form biliverdin IX alpha isomer. HO-1 and HO-2 utilized hematin and hematoheme as substrates but not intact cytochrome c.
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PMID:Characterization of two constitutive forms of rat liver microsomal heme oxygenase. Only one molecular species of the enzyme is inducible. 307 57

The concerted activity of two microsomal enzymes, heme oxygenase and NADPH-cytochrome c (P-450) reductase, is required for isomer-specific oxidation of heme molecule; heme oxygenase is commonly believed to be rate limiting in this activity. In this report, we provide evidence strongly suggesting the rate-limiting role of the reductase in oxidation of heme molecule in rat testis. In the testis and the liver of rats treated with Cd (20 mumol/kg, sc, 24 h) heme oxygenase activity, assessed by the formation of bilirubin, was decreased by 50% and increased by 7-fold, respectively. In these animals, the reductase activity was decreased by nearly 75% in the testis, but remained unchanged in the liver. Similarly, the reductase activity in the liver was not altered when heme oxygenase activity was increased by 20-fold in response to bromobenzene treatment. Addition of purified testicular reductase preparation (purified over 4000-fold), or hepatic reductase, to the testicular microsomes of Cd-treated rats obliterated the Cd-mediated inhibition of heme oxygenase activity. The chromatographic separation of heme oxygenase and the reductase of the testicular microsomal fractions revealed that the reductase activity was markedly decreased (75%) while the heme oxygenase activity, when assessed in the presence of exogenous reductase, was not affected by in vivo Cd treatment. In vitro, the membrane-bound reductase preparation obtained from the testis was more sensitive to the inhibitory effect of Cd than the liver preparation. However, the purified reductase preparations from the testis and the liver exhibited a similar degree of sensitivity to Cd. Based on the molar ratio of heme oxygenase to the reductase in the microsomal membranes of the liver and the testis it appeared that the testicular heme oxygenase, which is predominantly HO-2 isoform, interacts with the reductase less effectively than HO-1; in the induced liver, heme oxygenase is predominantly the HO-1 isoform. It is suggested that due to the low abundance of NADPH-cytochrome c (P-450) reductase and the apparently lower affinity of the enzyme for HO-2, the reductase exerts a regulatory action on heme oxygenase activity in the testis.
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PMID:Cadmium-mediated inhibition of testicular heme oxygenase activity: the role of NADPH-cytochrome c (P-450) reductase. 309 74

In this report we provide data, for the first time, demonstrating the conversion of the heme moiety of certain cytochrome P-450 and P-420 preparations, to biliverdin, catalyzed by heme oxygenase. We have used purified preparations of cytochromes P-450c, P-450b, P-450/P-420c, or P-450/P-420b as substrates in a heme oxygenase assay system reconstituted with heme oxygenase isoforms, HO-2 or HO-1, NADPH-cytochrome c (P-450) reductase, biliverdin reductase, NADPH, and Emulgen 911. With cytochrome P-450b or P-450/P-420b preparations, a near quantitative conversion of degraded heme to bile pigments was observed. In the case of cytochrome P-450/P-420c approximately 70% of the degraded heme was accounted for as bilirubin but only cytochrome P-420c was appreciably degraded. The role of heme oxygenase in this reaction was supported by the following observations: (i) bilirubin formation was not observed when heme oxygenase was omitted from the assay system; (ii) the rate of degradation of the heme moiety was at least threefold greater with heme oxygenase and NADPH-cytochrome c (P-450) reductase than that observed with reductase alone; and (iii) the presence of Zn- or Sn-protoporphyrins (2 microM), known competitive inhibitors of heme oxygenase, resulted in 70-90% inhibition of bilirubin formation.
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PMID:Rat liver cytochrome P-450b, P-420b, and P-420c are degraded to biliverdin by heme oxygenase. 312 60

Recently we reported on the presence of two isoforms of heme oxygenase in rat liver microsomes, referred to as HO-1 and HO-2, and that only HO-1 is inducible (Maines, M. D., Trakshel, G. M., and Kutty, R. K. (1986) J. Biol. Chem. 261, 411-419). Presently we report on the detection of two isoforms of the enzyme in rat testis and purification to near homogeneity of the noninducible isoform, HO-2. A comparative characterization of the liver HO-1 and the testicular HO-2 is also provided. The relative abundance of the isoforms in the two organs was dissimilar. In the testis, the predominant form was HO-2, and only minute amounts of HO-1 were detected. In the liver, however, a 1:2 ratio of HO-1 to HO-2 was noted. The activity of HO-2 in both organs was refractory to cadmium, an inducer of the hepatic HO-1. Under nondenaturing electrophoresis conditions, HO-2 showed a higher mobility than HO-1; on a sodium dodecyl sulfate-polyacrylamide gel, HO-2 displayed a higher monomeric Mr. The apparent Mr values for HO-2 and HO-1 were 36,000 and 30,000, respectively. The isoforms differed in immunochemical properties. Antiserum to the liver HO-1 did not recognize the testicular HO-2 when examined by double immunodiffusion or by Western immunoblotting. HO-2 was more sensitive to heat inactivation than HO-1. When exposed at 65 degrees C (10 min), 70% of HO-1 activity was retained; however, nearly 80% of HO-2 activity was lost. The apparent Km values for heme for HO-1 and HO-2 were 0.24 and 0.40 microM, respectively. HO-1 and HO-2 had similar requirements for cofactor and flavoprotein reductase and were inhibited by heme-ligands (CO, KCN, NaN3). HO-2 utilized as substrate, Fe-protoporphyrin, Fe-hematoporphyrin, and Fe-hematoporphyrin acetate; it did not degrade intact purified rat liver cytochromes b5 and P-450 LM2, catalase, cytochrome c, hemoglobin, or myoglobin.
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PMID:Purification and characterization of the major constitutive form of testicular heme oxygenase. The noninducible isoform. 352 62

Two heme oxygenase (HO) isozymes--HO-1, which is a heat shock protein (HSP32), and HO-2--catalyze the isomer-specific production of biliverdin IX alpha and carbon monoxide. The latter has the potential of functioning as a neurotransmitter, whereas the reduced form of biliverdin, bilirubin, has potent antioxidant activity. Formation of bilirubin is catalyzed by biliverdin reductase (BVR). The reductase is a unique enzyme in being dual pyridine nucleotide and dual pH dependent. Here, we show that the reductase is resistant to thermal stress at both the protein and message level. We further demonstrate that the reductase is coexpressed in cells that display HO-1 and/or HO-2 under normal conditions, as well as in regions and cell types that have the potential to express heat shock-inducible HO-1 protein. Exposure of male rats to 42 degrees C for 20 min did not decrease brain BVR activity, but caused a slight increase in NADPH- and NADH-dependent activities at 1 and 6 h following hyperthermia. High levels of the approximately 1.5-kb BVR mRNA were detected in control brain; it too displayed thermal tolerance. Similarly, the pattern of multiplicity of net charge variants of the enzyme purified from brain of heat-shocked rats did not differ from the control pattern. Immunochemical localization of BVR protein in normal brain correlated well with the presence of HO-1 and/or HO-2 throughout the forebrain, diencephalon, cerebellum, and brainstem regions. There were select neuronal and nonneuronal cells in the substantia nigra and cerebellum that did express the reductase under normal conditions, wherein no HO isozymes could be detected.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Biliverdin reductase is heat resistant and coexpressed with constitutive and heat shock forms of heme oxygenase in brain. 836 Jun 69

Biliverdin reductase (BVR) reduces heme oxygenase (HO) activity product, biliverdin, to bilirubin. BVR is unique in having dual pH/dual cofactor requirements. Using Escherichia coli-expressed human BVR and COS cells, we show that BVR is autophosphorylated and that phosphorylation is required for its activity. An "in blot" autophosphorylation assay showed that BVR is a renaturable phosphoprotein. Controls for the experiments were HO-1 and HO-2; both are phosphoproteins but are not autophosphorylated. Autophosphorylation was pH-dependent, with activity at pH 8.7 being most prominent. In addition, 2'(3')-O-(2,4,6-trinitrophenyl)adenosine 5'-triphosphate fluorescence titration of BVR gave a lower K(d) at pH 8.7 than at pH 7.4 (15.5 versus 28.0 micrometer). Mn(2+) was required for binding of the ATP analogue and for autophosphorylation; the autokinase activity was lost when treated at 60 degrees C for 10 min. The loss of transferred phosphates by alkaline treatment suggested that BVR is a serine/threonine kinase. Potato acid phosphatase treatment reversibly inactivated the enzyme. The enzyme was also inactivated by treatment with the serine/threonine phosphatase, protein phosphatase 2A; okadaic acid attenuated the inhibition. Titration of protein phosphatase 2A-released phosphates indicated a 1:6 molar ratio of BVR to phosphate. The BVR immunoprecipitated from COS cell lysates was a phosphoprotein, and its activity and phosphorylation levels increased in response to H(2)O(2). The results define a previously unknown mechanism for regulation of BVR activity and are discussed in the context of their relevance to heme metabolism.
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PMID:Human biliverdin reductase is autophosphorylated, and phosphorylation is required for bilirubin formation. 1127 40

Heme oxygenase (HO) cleaves the tetrapyrrolic ring of cellular heme moieties liberating carbon monoxide (CO) and equimolar amounts of free iron and biliverdin (BV). BV is in turn converted into bilirubin (BR) by the cytosolic enzyme BV reductase. Three HO isoforms have been described to date: HO-1, HO-2, and HO-3. All these isoforms are present in nervous tissue with different localizations and regulation. CO, the gaseous product of HO, exerts its biological effects through the activation of soluble guanylyl cyclase, but alternative signaling pathways, such as the activation of cyclooxygenase, have also been reported in the brain. In vitro and in vivo studies showed that CO, at the hypothalamic level, plays a key role in the modulation of stress response because it inhibits the release of antiinflammatory neuropeptides, such as corticotropin-releasing hormone and arginine vasopressin, and increases body temperature in rodents exposed to psychological stressors (stress fever). In the last few years, a new role of BR as an endogenously produced antioxidant has emerged, and several reports have shown that BR contributes to prevent cell damage mediated by reactive oxygen species, as well as nitric oxide and its congeners.
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PMID:Heme oxygenase and its products in the nervous system. 1534 48

Heme oxygenases (HO-1 and HO-2) catalyze the NADPH-cytochrome P(450) reductase (CPR)-dependent degradation of heme into iron, carbon monoxide, and biliverdin, which is reduced into bilirubin. Under basal conditions, HO-1 is often undetected and can be induced by numerous stress conditions. Although HO-2 is constitutively expressed, its activity appears to be regulated by post-translational modifications. HO activity has been associated with cellular protection, by which it degrades heme, a prooxidant, into bioactive metabolites. Under given circumstances, overexpression of HO-1 can render cells more sensitive to free radicals. Here, we investigated the properties of human HO isoforms that protect against oxidative stress. Considering that CPR can be a limiting factor for optimal HO activity, we tested stable HO-1 and HO-2 cell lines that derived from the CPR cells. Results indicate that the HO-1 and HO-2 cells are more resistant than controls to hemin and to the organic tert-butyl hydroperoxide, t-BuOOH. However, HO-1 cells are less resistant than HO-2 cells to hydrogen peroxide (H(2)O(2)). The levels of oxidatively modified proteins of HO-1 and HO-2 cells in response to t-BuOOH toxicity are identical, but the level of oxidatively modified proteins of HO-2 cells is less than that of HO-1 cells in response to H(2)O(2) toxicity. Performing subcellular fractionations revealed that HO-2 and CPR are found together in the microsomal fractions, whereas HO-1 is partially present in the microsome and also found in other fractions, such as the cytosol. These same findings were observed in non-transfected primary neurons where HO-1 proteins were chemically induced with 15-deoxy-Delta(12,14)-prostaglandin J(2) (15dPGJ(2)). The differences in subcellular localization of HO-1 and HO-2 could explain some of the discrepancies in their cellular activity and enzymatic protective mechanisms.
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PMID:Distinct protective mechanisms of HO-1 and HO-2 against hydroperoxide-induced cytotoxicity. 1558 75

The heme oxygenase isozymes, HO-1 and HO-2, oxidatively cleave the heme molecule to produce biliverdin and the gaseous messenger, CO. The cleavage results in the release of iron, a regulator of transferrin, ferritin, and nitric oxide (NO) synthase gene expression. Biliverdin reductase (BVR) then catalyzes the reduction of biliverdin, generating the potent intracellular antioxidant, bilirubin. We report an age-related decrease in HO-1 and HO-2 expression present in select brain regions including the hippocampus and the substantia nigra, that are involved in the high order cognitive processes of learning and memory. The age-related loss of monoxide-producing potential in select regions of the brain was not specific to the HO system but was also observed in neuronal NO-generating system. Furthermore, compared to 2-month old rats, the ability of aged brain tissue to respond to hypoxic/hyperthermia was compromised at both the protein and the transcription levels as judged by attenuated induction of HO-1 immunoreactive protein and its 1.8 Kb transcript. Neotrofin (AIT), a cognitive-enhancing and neuroprotective drug, caused a robust increase in HO-1 immunoreactive protein in select neuronal regions and increased the expression of HO-2 transcripts. The potential interplay between regulation of HO-2 gene expression and the serum levels of the adrenal steroids is discussed. We suggest the search for therapeutic agents that reverse the decline and aberrant stress response of HO enzymes may lead to effective treatment regimens for age-associated neuronal deficits.
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PMID:Regulation and expression of heme oxygenase enzymes in aged-rat brain: age related depression in HO-1 and HO-2 expression and altered stress-response. 1646 64


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