Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0026916 (MAC)
 5,226 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Structural and chemical properties of a flavodoxin from Anabaena PCC 7119 are described. The first 36 residues of the amino-terminal amino acid sequence have been determined and show extensive homology with flavodoxins isolated from other sources. Anabaena flavodoxin exhibits a net negative change (-3) in the helix-1 segment as found with other cyanobacterial flavodoxins Synechococcus 6301 (Anacystis nidulans) and Nostoc MAC, but in contrast to the net positive charge found in this region in the case of flavodoxins isolated from nitrogen-fixing bacteria (Azotobacter and Klebsiella). The FMN cofactor can be reversibly resolved from the apoprotein by trichloroacetic acid treatment. Apoflavodoxin, thus prepared, binds FMN with a Kd value of 0.1 nM and binds riboflavin with a decreased affinity (Kd = 5 microM) at pH 7.2. The apoprotein is stable in dilute solutions at pH values around 7 but readily denatures at pH 8 as judged from loss in flavin-binding ability and by ultraviolet circular dichroism spectroscopy. Oxidation-reduction potential studies at pH values of 7 and 8 show OX/SQ couples of -195 mV and -255 mV, respectively, and show SQ/HQ couples of -390 mV and -418 mV, respectively. From these data, the binding constant for the FMN semiquinone is calculated to be approx. 5-fold tighter and the binding of the FMN hydroquinone is approx. 10(5)-fold weaker than that of the oxidized FMN to the apoprotein. Anabaena flavodoxin functions as an effective mediator of electron transfer from ferredoxin-NADP(+)-reductase to cytochrome c with a turnover number [4.5-5) x 10(3) min-1); a values similar to that determined for Anabaena ferredoxin. The flavodoxin binds tightly to the reductase with Kd values of 6.4 and 8.5 microM at pH values of 7.0 and 8.0, respectively.
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PMID:Structural and chemical properties of a flavodoxin from Anabaena PCC 7119. 211 31

In this study, the enzymology of mitomycin C (MMC) bioactivation in two murine colon adenocarcinomas, MAC 16 and MAC 26, was examined. Subcellular quinone reductase assessment via cytochrome c reduction confirmed a number of active enzymes. MAC 16 exhibited 22-fold greater levels of cytosolic DT-diaphorase than MAC 26, while microsomal NADPH:cytochrome P-450 reductase levels were similar in both tumour types. Metabolism of MMC by subcellular fractions isolated from both MAC 16 and MAC 26 was quantitated by monitoring the formation of the principle metabolite 2,7-diaminomitosene (2,7-DM) via high-performance liquid chromatography (HPLC). In MAC 16 only, activity displaying the properties of cytosolic DT-diaphorase and microsomal NADPH:cytochrome P-450 reductase was detected and confirmed, using the enzyme inhibitors dicoumarol and cytochrome P-450 reductase antiserum, respectively. The highest level of MMC metabolism was associated with the mitochondrial fraction from both tumours and was the sole enzyme activity detected in MAC 26. The greatest mitochondrial drug metabolism was achieved in the presence of NADPH as cofactor and hypoxia (MAC 16-specific activity, 3.67 +/- 0.58 nmol/30 min/mg; MAC 26 specific-activity, 3.87 +/- 0.71 nmol/30 min/mg) and was unaffected by the addition of the inhibitors dicoumarol and cytochrome P-450 reductase antiserum. NADH-dependent mitochondrial activity was only observed in MAC 16 at approximately 4-fold less than that seen with NADPH. MAC 26 homogenate incubations displayed enhanced metabolism under hypoxia, presumably due to the presence of the identified mitochondrial enzyme. MAC 16 homogenates showed no increase in metabolism under hypoxia, suggesting that other enzyme(s) may be predominant. These data indicate the presence of a novel mitochondrial one-electron reductase capable of metabolising MMC in MAC 16 and MAC 26.
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PMID:Enzymology of mitomycin C metabolic activation in tumour tissue. Characterization of a novel mitochondrial reductase. 868 77

EO9 is a novel bioreductive drug which has recently undergone extensive clinical evaluation. Its mechanism of action remains to be clearly defined. Antitumour activity of EO9 has been determined in 2 human colon cancer xenografts (HT-29 and BE) and 2 murine colon adenocarcinomas (MAC 16 and 26) after intratumoural injection of 250 microg of drug. Levels of the major bioreductive enzymes (DT-diaphorase, cytochrome P-450 reductase and cytochrome b5 reductase) were measured in tumours using cytochrome c reduction and menadione as the intermediate electron acceptor. There was no correlation between chemosensitivity (T/C: HT-29, 15%; BE, 27%; MAC 16, 33% and MAC 26, 60%) and enzyme activity (r2 = 0.47 for DT-diaphorase, r2 = 0.1 for cytochrome P-450 reductase and r2 = 0.52 for cytochrome b5 reductase). Drug metabolism was followed in vitro using tumour homogenates incubated under aerobic and anaerobic conditions. Four metabolites were identified by HPLC and characterised bv UV-visible spectroscopy. With the exception of the hydrolysis product EO5A, all other metabolites appeared to be drug adducts. No correlation was observed between the kinetics of metabolite formation and antitumour activity. A good correlation (r2 = 0.86) was found with the rate of disappearance of parent drug and antitumour activity. These data show that the overall capacity of a tumour to metabolise EO9 is the most important determinant of antitumour activity rather than the expression of the major bioreductive enzymes and that the parent drug rather than a metabolite leads to the active form of the drug.
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PMID:Pharmacological and biochemical determinants of the antitumour activity of the indoloquinone EO9. 948 90

Programmed cell death or apoptosis is central to many physiological processes and pathological conditions such as organogenesis, tissue homeostasis, cancer, and neurodegenerative diseases. Bcl-2 family proteins tightly control this cell death program by regulating the permeabilization of the mitochondrial outer membrane and, hence, the release of cytochrome c and other pro-apoptotic factors. Control of the formation of the mitochondrial apoptosis-induced channel, or MAC, is central to the regulation of apoptosis by Bcl-2 family proteins. MAC is detected early in apoptosis by patch clamping the mitochondrial outer membrane. The focus of this review is on the regulation of MAC activity by Bcl-2 family proteins. The role of MAC as the putative cytochrome c release channel during early apoptosis and insights concerning its molecular composition are also discussed.
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PMID:Regulation of the mitochondrial apoptosis-induced channel, MAC, by BCL-2 family proteins. 1605 9

Permeabilization of the mitochondrial outer membrane is a crucial event during apoptosis. It allows the release of proapoptotic factors, like cytochrome c, from the intermembrane space, and represents the commitment step in apoptosis. The mitochondrial apoptosis-induced channel, MAC, is a high-conductance channel that forms during early apoptosis and is the putative cytochrome c release channel. Unlike activation of the permeability transition pore, MAC formation occurs without loss of outer membrane integrity and depolarization. The single channel behavior and pharmacology of reconstituted MAC has been characterized with patch-clamp techniques. Furthermore, MAC's activity is compared to that detected in mitochondria inside the cells at the time cytochrome c is released. Finally, the regulation of MAC by the Bcl-2 family proteins and insights concerning its molecular composition are also discussed.
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PMID:The role of the mitochondrial apoptosis induced channel MAC in cytochrome c release. 1616 72

Respiratory particles containing an aa(3)-type cytochrome oxidase were prepared from Anacystis nidulans, Synechocystis 6714, Synechococcus lividus, Anabaena variabilis, Nostoc sp. strain MAC, Nostoc muscorum, and Mastigocladus laminosus. Oxidation of c-type cytochromes by membrane preparations of the different blue-green algae was observed using purified cytochromes from horse heart, Candida krusei, tuna, Saccharomyces oviformis, Rhodospirillum rubrum, Rhodospirillum molischianum, Rhodopseudomonas palustris, Rhodocyclus purpureus, Paracoccus denitrificans, Anacystis nidulans, Anabaena variabilis, Euglena gracilis, and Scenedesmus obliquus. Rapid oxidations were consistently observed with the mitochondrial c-type cytochromes (horse heart cytochrome c reacts most rapidly) and with cytochromes c(2) from Rhodopseudomonas palustris and Rhodocyclus purpureus; in contrast, the cytochrome c(2) from Rhodospirillum rubrum and the plastidic cytochromes from E. gracilis and Scendesmus obliquus were inactive with all membrane preparations. All reactions were inhibited by low concentrations of KCN, NaN(3), and CO, and they were activated by Tween 80, thus indicating participation of the terminal oxidase. The results are discussed in view of the spectral similarities between the terminal oxidase of blue-green algae and the mitochondrial aa(3)-type cytochrome oxidase of plants and other eukaryotes.
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PMID:Oxidation of c-Type Cytochromes by the Membrane-Bound Cytochrome Oxidase (Cytochrome aa(3)) of Blue-Green Algae. 1666 53

MAC (mitochondrial apoptosis-induced channel) forms in the mitochondrial outer membrane and unleashes cytochrome c to orchestrate the execution of the cell. MAC opening is the commitment step of intrinsic apoptosis. Hence closure of MAC may prevent apoptosis. Compounds that blocked the release of fluorescein from liposomes by recombinant Bax were tested for their ability to directly close MAC and suppress apoptosis in FL5.12 cells. Low doses of these compounds (IC50 values ranged from 19 to 966 nM) irreversibly closed MAC. These compounds also blocked cytochrome c release and halted the onset of apoptotic markers normally induced by IL-3 (interleukin-3) deprivation or staurosporine. Our results reveal the tight link among MAC activity, cytochrome c release and apoptotic death, and indicate this mitochondrial channel is a promising therapeutic target.
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PMID:MAC inhibitors suppress mitochondrial apoptosis. 1969 47

The death of one cell can precipitate the death of nearby cells in a process referred to as the bystander effect. We investigated whether mitochondrial apoptosis generated a bystander effect and, if so, by which pathway. Microinjection with cytochrome c mimicked function of the mitochondrial apoptosis-induced channel MAC and caused apoptosis of both target and nearby osteoblasts. This effect was suppressed by inhibiting gap junction intercellular communication. A bystander effect was also observed after exogenous expression of tBid, which facilitates MAC formation and cytochrome c release. Interestingly, in connexin-43 deficient osteoblasts, microinjection of cytochrome c induced apoptosis only in the target cell. These findings indicate that a death signal was generated downstream of MAC function and was transmitted through gap junctions to amplify apoptosis in neighboring cells. This concept may have implications in development of new therapeutic approaches.
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PMID:Mitochondrial apoptosis is amplified through gap junctions. 1976 91

Apoptosis is an elemental form of programmed cell death; it is fundamental to higher eukaryotes and essential to mechanisms controlling tissue homeostasis. Apoptosis is also involved in many pathologies including cancer, neurodegenerative diseases, aging, and infarcts. This cell death program is tightly regulated by Bcl-2 family proteins by controlling the formation of the mitochondrial apoptosis-induced channel or MAC. Assembly of MAC corresponds to permeabilization of the mitochondrial outer membrane, which is the so called commitment step of apoptosis. MAC provides the pathway through the mitochondrial outer membrane for the release of cytochrome c and other pro-apoptotic factors from the intermembrane space. While overexpression of anti-apoptotic Bcl-2 eliminates MAC activity, oligomers of the pro-apoptotic members Bax and/or Bak are essential structural component(s) of MAC. Assembly of MAC from Bax or Bak was monitored in real time by directly patch-clamping mitochondria with micropipettes containing the sentinel tBid, a direct activator of Bax and Bak. Herein, a variety of high affinity inhibitors of MAC (iMAC) that may prove to be crucial tools in mechanistic studies have recently been identified. This review focuses on characterization of MAC activity, its regulation by Bcl-2 family proteins, and a discussion of how MAC can be pharmacologically turned on or off depending on the pathology to be treated.
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PMID:MAC and Bcl-2 family proteins conspire in a deadly plot. 2008 86

Apoptosis is a phenomenon fundamental to higher eukaryotes that is integral to such diverse cellular processes as tissue homeostasis, organogenesis, and response to toxins. The release from mitochondria of apoptotic factors such as cytochrome c is a key step during apoptosis of most cells. Cytochrome c release occurs through the MAC (mitochondrial apoptosis-induced channel), a pore which forms in the mitochondrial outer membrane during early apoptosis and is exquisitely regulated by the Bcl-2 family of proteins. This unit presents basic and advanced tools for detecting MAC and defining its regulation by Bcl-2 family proteins and pharmacological agents. Protocols include the use of time-lapse video-microscopy to monitor the onset of apoptosis in living cells and patch-clamp techniques for mitochondria or proteoliposomes containing mitochondrial proteins, which allow direct detection of MAC. These approaches enable an evaluation of the role of MAC and mitochondria in apoptosis of a variety of cell types by many inducers.
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PMID:Detection of the mitochondrial apoptosis-induced channel (MAC) and its regulation by Bcl-2 family proteins. 2094 3


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