Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.14.99.3 (heme oxygenase)
4,196 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Staphylococcus aureus requires iron for growth and utilizes heme as a source of iron during infection. Staphylococcal surface proteins capture hemoglobin, release heme from hemoglobin and transport this compound across the cell wall envelope and plasma membrane into the bacterial cytoplasm. Here we show that Staphylococcus aureus isdG and isdI encode cytoplasmic proteins with heme binding properties. IsdG and IsdI cleave the tetrapyrrol ring structure of heme in the presence of NADPH cytochrome P450 reductase, thereby releasing iron. Further, IsdI complements the heme utilization deficiency of a Corynebacterium ulcerans heme oxygenase mutant, demonstrating in vivo activity of this enzyme. Although Staphylococcus epidermidis, Listeria monocytogenes, and Bacillus anthracis encode homologues of IsdG and IsdI, these proteins are not found in other bacteria or mammals. Thus, it appears that bacterial pathogens evolved different strategies to retrieve iron from scavenged heme molecules and that staphylococcal IsdG and IsdI represent examples of bacterial heme-oxygenases.
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PMID:IsdG and IsdI, heme-degrading enzymes in the cytoplasm of Staphylococcus aureus. 1457 Sep 22

Although hypoxia induces heme oxygenase (HO)-1 mRNA and protein expression in many cell types, recent studies in our laboratory using human placental tissue have shown that a preexposure to hypoxia does not affect subsequent HO enzymatic activity for optimized assay conditions (20% O2; 0.5 mM NADPH; 25 microM methemalbumin) or HO-1 protein content. One of the consequences of impaired blood flow is glucose deprivation, which has been shown to be an inducer of HO-1 expression in HepG2 hepatoma cells. The objective of the present study was to test the effects of a 24-h preexposure to glucose-deprived medium, in 0.5 or 20% O2, on HO protein content and enzymatic activity in isolated chorionic villi and immortalized HTR-8/SVneo first-trimester trophoblast cells. HO protein content was determined by Western blot analysis, and microsomal HO enzymatic activity was measured by assessment of the rate of CO formation. HO enzymatic activity was increased (P < 0.05) in both placental models after 24-h preexposure to glucose-deficient medium in 0.5 or 20% O2. Preexposure (24 h) in a combination of low O2 and low glucose concentrations decreased the protein content of the HO-1 isoform by 59.6% (P < 0.05), whereas preexposure (24 h) to low glucose concentration alone increased HO-2 content by 28.2% in chorionic villi explants (P < 0.05). In this preparation, HO enzymatic activity correlated with HO-2 protein content (r = 0.825). However, there was no correlation between HO-2 protein content and HO enzymatic activity in HTR-8/SVneo trophoblast cells preexposed to 0.5% O2 and low glucose concentration for 24 h. These findings indicate that the regulation of HO expression in the human placenta is a complex process that depends, at least in part, on local glucose and oxygen concentrations.
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PMID:Effect of glucose and oxygen deprivation on heme oxygenase expression in human chorionic villi explants and immortalized trophoblast cells. 1461 5

We tested the hypothesis that the status of NO synthesis influences the renal heme-heme oxygenase system. Studies were conducted in untreated rats and rats treated with the NO synthesis inhibitor N(G)-nitro-L-arginine methyl ester for 2 days. Treated and untreated rats were contrasted in terms of renal expression of heme oxygenase-1 and -2, renal carbon monoxide (CO)-generating activity, and urinary CO concentration and excretion rate. Heme oxygenase-1 and -2 proteins were similarly expressed in the kidneys of untreated and treated rats. In contrast, the NADPH-dependent component of the CO-generating activity of renal homogenates incubated with heme (a measure of heme oxygenase activity) was higher (P<0.05) in kidneys from rats treated with the NO synthesis inhibitor relative to corresponding data in untreated rats (1015+/-95 versus 379+/-111 pmol CO/mg per hour). Similarly, relative to corresponding data in untreated rats, rats treated with the NO synthesis inhibitor displayed increased (P<0.05) urinary CO concentration (920+/-174 versus 2286+/-472 pmol/mL) and urinary CO excretion (4.7+/-0.4 versus 14.3+/-2.7 pmol/min). This study demonstrates that NO synthesis inhibition upregulates the urinary concentration and excretion rate of CO, and the HO-dependent generation of CO by renal homogenates, without affecting the expression of renal heme oxygenase isoforms. Our findings imply that endogenous NO is an inhibitory regulator of renal CO generation by HO.
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PMID:Nitric oxide synthesis inhibition promotes renal production of carbon monoxide. 1469 98

We cloned a cDNA for a Drosophila melanogaster homologue of mammalian heme oxygenase (HO) and constructed a bacterial expression system of a truncated, soluble form of D. melanogaster HO (DmDeltaHO). The purified DmDeltaHO degraded hemin to biliverdin, CO and iron in the presence of reducing systems such as NADPH/cytochrome P450 reductase and sodium ascorbate, although the reaction rate was slower than that of mammalian HOs. Some properties of DmHO, however, are quite different from other known HOs. Thus DmDeltaHO bound hemin stoichiometrically to form a hemin-enzyme complex like other HOs, but this complex did not show an absorption spectrum of hexa-coordinated heme protein. The absorption spectrum of the ferric complex was not influenced by changing the pH of the solution. Interestingly, an EPR study revealed that the iron of heme was not involved in binding heme to the enzyme. Hydrogen peroxide failed to convert it into verdoheme. A spectrum of the ferrous-CO form of verdoheme was not detected during the reaction from hemin under oxygen and CO. Degradation of hemin catalyzed by DmDeltaHO yielded three isomers of biliverdin, of which biliverdin IXalpha and two other isomers (IXbeta and IXdelta) accounted for 75% and 25%, respectively. Taken together, we conclude that, although DmHO acts as a real HO in D. melanogaster, its active-site structure is quite different from those of other known HOs.
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PMID:Unique features of recombinant heme oxygenase of Drosophila melanogaster compared with those of other heme oxygenases studied. 1509 10

Human intestinal Caco-2 cells metabolize and detoxify NO via a dioxygen- and NADPH-dependent, cyanide- and CO-sensitive pathway that yields nitrate. Enzymes catalyzing NO dioxygenation fractionate with membranes and are enriched in microsomes. Microsomal NO metabolism shows apparent KM values for NO, O2, and NADPH of 0.3, 9, and 2 microM, respectively, values similar to those determined for intact or digitonin-permeabilized cells. Similar to cellular NO metabolism, microsomal NO metabolism is superoxide-independent and sensitive to heme-enzyme inhibitors including CO, cyanide, imidazoles, quercetin, and allicin-enriched garlic extract. Selective inhibitors of several cytochrome P450s and heme oxygenase fail to inhibit the activity, indicating limited roles for a subset of microsomal heme enzymes in NO metabolism. Diphenyleneiodonium and cytochrome c(III) inhibit NO metabolism, suggesting a role for the NADPH-cytochrome P450 oxidoreductase (CYPOR). Involvement of CYPOR is demonstrated by the specific inhibition of the NO metabolic activity by inhibitory anti-CYPOR IgG. In toto, the results suggest roles for a microsomal CYPOR-coupled and heme-dependent NO dioxygenase in NO metabolism, detoxification, and signal attenuation in mammalian cells.
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PMID:Nitric oxide metabolism in mammalian cells: substrate and inhibitor profiles of a NADPH-cytochrome P450 oxidoreductase-coupled microsomal nitric oxide dioxygenase. 1520 93

The heme oxygenase (HO) and nitric oxide synthase (NOS) enzymes generate the gaseous signaling molecules carbon monoxide (CO) and nitric oxide, respectively. Constitutive NOSs localize to caveolae, and their activities are modulated by caveolin-1. Nothing is known of the localization of the inducible heme oxygenase-1 (HO-1) in plasma membrane caveolae. Thus, we examined the distribution and subcellular localization of HO-1, biliverdin reductase (BVR), and NADPH:cytochrome P450 reductase (NPR) in pulmonary artery endothelial cells. Each of these proteins localized in part to plasma membrane caveolae in endothelial cells. Inducers of HO-1 or overexpression of HO-1 increased the content of this protein in a detergent-resistant fraction containing caveolin-1. Inducible HO activity appeared in plasma membrane, cytosol, and isolated caveolae. In addition, caveolae contained endogenous BVR activity, supporting the same compartmentalization of both enzymes. Caveolin-1 physically interacted with HO-1, as shown by coimmunoprecipitation studies. HO activity dramatically increased in cells expressing caveolin-1 antisense transcripts, suggesting a negative regulatory role for caveolin-1. Conversely, caveolin-1 expression attenuated LPS-inducible HO activity. Since their initial characterization in 1969, HO enzymes have been described as endoplasmic reticulum-associated proteins. We demonstrate for the first time the localization of heme degradation enzymes to plasma membrane caveolae, and present novel evidence that caveolin-1 interacts with and modulates HO activity.
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PMID:Caveolae compartmentalization of heme oxygenase-1 in endothelial cells. 1522 68

Nitric oxide synthases (NOS) are hemoproteins that catalyze the reaction of L-arginine to L-citrulline and nitric oxide. N-(3-(Aminomethyl)benzyl)acetamidine (1400W) was reported to be a slow, tight-binding, and highly selective inhibitor of iNOS in vitro and in vivo. Previous mechanistic studies reported that 1400W was recovered quantitatively after iNOS fully lost its activity and modification to iNOS was not detected. Here, it is shown that 1400W is a time-, concentration-, and NADPH-dependent irreversible inactivator of iNOS. HPLC-electrospray mass spectrometric analysis of the incubation mixture of iNOS with 1400W shows both loss of heme cofactor and formation of biliverdin, as was previously observed for iNOS inactivation by another amidine-containing compound, N5-(1-iminoethyl)-L-ornithine (L-NIO). The amount of biliverdin produced corresponds to the amount of heme lost by 1400W inactivation of iNOS. A convenient MS/MS-HPLC methodology was developed to identify the trace amount of biliverdin produced by inactivation of iNOS with either 1400W or L-NIO to be biliverdin IXalpha out of the four possible regioisomers. Two mechanisms were previously proposed for iNOS inactivation by L-NIO: (1) uncoupling of the heme peroxide intermediate, leading to destruction of the heme to biliverdin; (2) abstraction of a hydrogen atom from the amidine methyl group followed by attachment to the heme cofactor, which causes the enzyme to catalyze the heme oxygenase reaction. The second mechanistic proposal was ruled out by inactivation of iNOS with d3-1400W, which produced no d2-1400W. Detection of carbon monoxide as one of the heme-degradation products further excludes the covalent heme adduct mechanism. On the basis of these results, a third mechanism is proposed in which the amidine inactivators of iNOS bind as does substrate L-arginine, but because of the amidine methyl group, the heme peroxy intermediate cannot be protonated, thereby preventing its conversion to the heme oxo intermediate. This leads to a change in the enzyme mechanism to one that resembles that of heme oxygenase, an enzyme known to convert heme to biliverdin IXalpha. This appears to be the first example of a compound that causes irreversible inactivation of an enzyme without itself becoming modified in any way.
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PMID:Mechanism of inactivation of inducible nitric oxide synthase by amidines. Irreversible enzyme inactivation without inactivator modification. 1565 23

Two isoforms of a heme oxygenase gene, ho1 and ho2, with 51% identity in amino acid sequence have been identified in the cyanobacterium Synechocystis sp. PCC 6803. Isoform-1, Syn HO-1, has been characterized, while isoform-2, Syn HO-2, has not. In this study, a full-length ho2 gene was cloned using synthetic DNA and Syn HO-2 was demonstrated to be highly expressed in Escherichia coli as a soluble, catalytically active protein. Like Syn HO-1, the purified Syn HO-2 bound hemin stoichiometrically to form a heme-enzyme complex and degraded heme to biliverdin IXalpha, CO and iron in the presence of reducing systems such as NADPH/ferredoxin reductase/ferredoxin and sodium ascorbate. The activity of Syn HO-2 was found to be comparable to that of Syn HO-1 by measuring the amount of bilirubin formed. In the reaction with hydrogen peroxide, Syn HO-2 converted heme to verdoheme. This shows that during the conversion of hemin to alpha-meso-hydroxyhemin, hydroperoxo species is the activated oxygen species as in other heme oxygenase reactions. The absorption spectrum of the hemin-Syn HO-2 complex at neutral pH showed a Soret band at 412 nm and two peaks at 540 nm and 575 nm, features observed in the hemin-Syn HO-1 complex at alkaline pH, suggesting that the major species of iron(III) heme iron at neutral pH is a hexa-coordinate low spin species. Electron paramagnetic resonance (EPR) revealed that the iron(III) complex was in dynamic equilibrium between low spin and high spin states, which might be caused by the hydrogen bonding interaction between the distal water ligand and distal helix components. These observations suggest that the structure of the heme pocket of the Syn HO-2 is different from that of Syn HO-1.
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PMID:Protein expressed by the ho2 gene of the cyanobacterium Synechocystis sp. PCC 6803 is a true heme oxygenase. Properties of the heme and enzyme complex. 1569 34

AZD3582 [4-(nitrooxy)-butyl-(2S)-2-(6-methoxy-2-naphthyl)-propanoate] is a COX-inhibiting nitric oxide donator (CINOD). Incubation of human endothelial cells (derived from umbilical cord) with AZD3582 (10-100muM) led to increased expression of heme oxygenase (HO)-1 mRNA and protein. Heme oxygenase-1 (HO-1) is a crucial mediator of antioxidant and tissue-protective actions. In contrast, naproxen (a non-selective NSAID) and rofecoxib (a selective inhibitor of COX-2), did not affect HO-1 expression. Pre-treating endothelial cells with AZD3582 at concentrations that were effective at inducing HO-1 also reduced NADPH-dependent production of oxygen radicals. Antioxidant activity in the endothelial cells persisted after AZD3582 had been washed out from the incubation medium. When added exogenously to the cells at low micromolar concentrations, the HO-1 metabolite, bilirubin, virtually abolished NADPH-dependent oxidative stress. AZD3582-induced blockade of free-radical formation was reversed in the presence of the HO-1 inhibitor, tin protoporphyrin-IX (SnPP). Similar results were obtained in human gastric mucosal cells (KATO-III). Our results demonstrate that HO-1 is a novel target of AZD3582.
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PMID:AZD3582 increases heme oxygenase-1 expression and antioxidant activity in vascular endothelial and gastric mucosal cells. 1591 Dec 18

Carbon monoxide (CO) is produced during the heme catabolism by heme oxygenase. In brain or blood vessels, CO functions as a neurotransmitter or an endothelial-derived relaxing factor. To verify whether crystallographically proposed CO-trapping sites of rat and cyanobacterial heme oxygenase-1 really work, heme catabolism by heme oxygenase-1 from rat and cyanobacterial Synechocystis sp. PCC 6803 has been scrutinized in the presence of 2-propanol. If 2-propanol occupies the trapping sites, formation of CO-bound verdoheme should be enhanced. Although effects of 2-propanol on the rat heme oxygenase-1 reaction were obscure, the reaction of cyanobacterial enzyme in the presence of NADPH/ferredoxin reductase/ferredoxin was apparently affected. Relative amount of CO-verdoheme versus CO-free verdoheme detected by optical absorption spectra increased as the equivalent of 2-propanol increased, thereby supporting indirectly that the hydrophobic cavity in cyanobacterial enzyme traps CO to reduce CO inhibition of verdoheme degradation.
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PMID:Evidence for the hydrophobic cavity of heme oxygenase-1 to be a CO-trapping site. 1612 69


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