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Biomedical subjects

R E Ebel

Publications and source records attributed to R E Ebel.

At least 19 recordsLinked to original sources
PubMed1996

Spectroscopical and functional characterization of the hemoglobin of Nostoc commune (UTEX 584 (Cyanobacterial).

Structural analysis of a monomeric hemoglobin from the cyanobacterium Nostoc commune strain UTEX 584, cyanoglobin (Potts et al. (1992) Science 256, 1690-1692), is presented. Cyanoglobin binds molecular oxygen reversibly, with high oxygen affinity and non-cooperativity. There was no evidence for decreased stability of the pigment at 37 degrees C. Cyanoglobin-specific antibodies showed no cross-reactivity with two reference hemoglobins, leghemoglobin a and sperm whale myoglobin. The absorption spectral properties of cyanoglobin differ significantly from those of the two reference hemoglobins. The spectrum of oxy-cyanoglobin most closely resembles that of an oxy-hemoglobin from the protozoan Tetrahymena pyriformis, a hemoprotein that shares substantial amino-acid sequence identity with cyanoglobin. Met-cyanoglobin possesses spectral characteristics at pH 7.0-9.0 that resemble those of the alkaline met-hemoglobin (a putative hemichrome) of another protozoan, Paramecium caudatum. The spin-state character of met-cyanoglobin is pH-dependent. Met-cyanoglobin does not coordinate the strong-field ligands, cyanide and azide, at pH 7.0. The capacity of cyanoglobin to coordinate cyanide increased with decreasing pH. Far-UV CD spectra of cyanoglobin are indicative of a protein with a significant amount of alpha-helical structure. Data from Soret-region CD spectra suggest that the orientations of the heme moieties in cyanoglobin and leghemoglobin a are similar to one another.

Blotting, Western↗
PubMed1992

Myoglobin in a cyanobacterium.

Myoglobin was found in the nitrogen-fixing cyanobacterium Nostoc commune. This cyanobacterial myoglobin, referred to as cyanoglobin, was shown to be a soluble hemoprotein of 12.5 kilodaltons with an amino acid sequence that is related to that of myoglobins from two lower eukaryotes, the ciliated protozoa Paramecium caudatum and Tetrahymena pyriformis. Cyanoglobin is encoded by the glbN gene, which is positioned between nifU and nifH-two genes essential for nitrogen fixation-in the genome of Nostoc. Cyanoglobin was detected in Nostoc cells only when they were starved for nitrogen and incubated microaerobically.

Amino Acid Sequence↗
PubMed1989

Pyrazole treatment of rats potentiates CCL4-but not CHCL3-hepatotoxicity.

Rats were treated with pyrazole to increase the liver content of the "alcohol-inducible" form of cytochrome P-450. This treatment increased the sensitivity of these animals to CCl4-hepatotoxicity assessed by increases in SGPT and SGOT levels and decreases in microsomal cytochrome P-450 and aniline p-hydroxylase activity. However, the hepatotoxicity of CHCl3 was not increased by pyrazole-treatment. These data are consistent with the hypothesis that the "alcohol-inducible" form of cytochrome P-450 is capable of CCl4- but not CHCl3-activation.

Alanine Transaminase↗
PubMed1987

Chloroform hepatotoxicity in the Mongolian gerbil.

CHCl3 hepatotoxicity was studied in the male Mongolian gerbil and compared to that in the male Sprague-Dawley strain rat. Based on elevations in serum transaminase activities in response to CHCl3 exposure, control gerbils were more sensitive to CHCl3 than were gerbils treated with phenobarbital, chlordecone, mirex, or 3-methylcholanthrene. The increased sensitivity of the control relative to the induced gerbil was consistent with earlier observations of CCl4 hepatotoxicity (Ebel, R. E., and McGrath, E. A., 1984, Toxicol, Lett., 22, 205-210). Microsomal enzyme concentrations or activities were not decreased in the control or induced gerbils in response to CHCl3 exposures of up to 200 microliter/kg. At a dose of 500 microliter/kg, cytochrome P-450 and its reductase were decreased by about 25% in the chlordecone-induced gerbil. In contrast, chlordecone- and phenobarbital-induced rats were sensitive to CHCl3 as evidenced by marked elevations in serum transaminase activities, decreases in microsomal enzyme concentrations or activities, and a transient decrease in hepatic nonprotein sulfhydryl groups. Control rats were insensitive to CHCl3. Histopathological changes in the livers of these animals were consistent with alterations in the biochemical parameters measured. The relationship between sensitivity to the hepatotoxic effects of CHCl3 and CCl4 was different for the gerbil and rat.

Alanine Transaminase↗
PubMed1987

Benzo[a]pyrene metabolism in the Mongolian gerbil: influence of chlordecone and mirex induction.

1. The metabolism of benzo[a]pyrene (BP) by gerbil hepatic microsomes is increased following induction by phenobarbital (PB), chlordecone, mirex and 3-methylcholanthrene (3-MC). 2. By several criteria including the influence of alpha-naphthoflavone (alpha-NF) on BP-hydroxylase activity and BP-metabolite profiles, the cytochromes P-450 responsible for benzo[a]pyrene metabolism appear to be similar in microsomes isolated from PB-, chlordecone-, or mirex-treated gerbils. The cytochromes P-450 present in microsomes isolated from control animals and those treated with 3-MC are different from each other and from those present in PB, chlordecone, or mirex microsomes by the same criteria. 3. Of the inducers used, only PB induced microsomal epoxide hydrolase activity.

Animals↗
PubMed1987

Influence of chlordecone and mirex exposure on benzo[a]pyrene metabolism of rat-liver microsomes.

The metabolism of benzo[a]pyrene (BP) in hepatic microsomes isolated from rats exposed to chlordecone or mirex was compared to that of untreated rats and rats treated with 3-methylcholanthrene (3-MC) or phenobarbital (PB). Treatment with chlordecone resulted in a two- to three-fold increase in cytochrome P-450 content but the BP-hydroxylase activity per mg microsomal protein was unaffected. Addition of alpha-naphthoflavone (alpha-NF) or chlordecone caused changes in BP-hydroxylase activity indicating that chlordecone-induced cytochromes P-450 were similar to control. H.p.l.c. analyses of BP metabolites confirmed this similarity. Treatment with mirex caused a two-fold induction of cytochrome P-450, and BP-hydroxylase activity expressed per mg microsomal protein was increased 1.3-fold. Addition of chlordecone or alpha-NF caused changes in BP-hydroxylase activity, indicating differences between control and mirex-induced cytochromes P-450. H.p.l.c. analyses of BP metabolites confirmed this difference. Treatment with chlordecone or mirex increased microsomal epoxide hydrolase activity three-fold. Chlordecone accumulated in hepatic nuclei.

Animals↗
PubMed1984

Hepatic microsomal p-nitroanisole O-demethylase. Effects of chlordecone or mirex induction in male and female rats.

The effects of chlordecone (CD) or mirex treatment on the hepatic microsomal monooxygenase system of male and female rats were investigated, and kinetic parameters (apparent Vmax and apparent Km) for p-nitroanisole O-demethylase were studied in detail. Both pesticides elevated the levels of cytochrome P-450 in a time- and dose-dependent manner. The maximum rate of p-nitroanisole metabolism in males was increased about 100 and 50% and the apparent Km was elevated about 40- and 18-fold by CD and mirex respectively. p-Nitroanisole metabolism in females was reduced slightly by treatment with either agent, and the apparent Km was increased about 14-fold by CD but was relatively unaffected by mirex treatment.

Animals↗
PubMed1984

CCl4-hepatotoxicity in the Mongolian gerbil: influence of monooxygenase system induction.

The effects of chlordecone (CD), mirex or phenobarbital (PB) treatment of male Mongolian gerbils on CCl4-hepatotoxicity were determined. These monooxygenase inducers did not potentiate CCl4-hepatotoxicity in the gerbil although phenobarbital and CD are known potentiators in the rat. The control gerbil was more sensitive to CCl4-hepotoxicity than the control rat as reflected in loss of cytochrome (cyt) P-450 and increases in SGOT and SGPT. In addition, CCl4 treatment of the control gerbils resulted in significant reductions in cyt b5 and NADPH-cyt P-450 levels, a phenomenon not observed in the rat.

Alanine Transaminase↗
PubMed1977

Evidence that puriified liver microsomal cytochrome P-450 is a one-electron acceptor.

Two forms of highly purified liver microsomal cytochrome P-450, P-450LM2, and P-450LM4, have been titrated with standardized solutions of sodium dithionite under anaerobic conditions. Only 1 electron was consumed per hemin molecule, and reoxidation of the reduced heme is accompanied by the transfer of 1 electron to oxidizing agents such as cytochrome c, cytochrome b5, or potassium ferricyanide. The present results are in disagreement with earlier dithionite titrations and reoxidation experiments which indicate that liver microsomal cytochrome P-450 is a 2-electron acceptor, but are in accord with previous potentimetric titrations and product yield data which indicate that this hemeprotein is a 1-electron acceptor. The cause for the discrepancy between the present and previous results is not fully understood.

Animals↗
PubMed1976

Temperature dependence of cytochrome P-450 reduction. A model for NADPH-cytochrome P-450 reductase:cytochrome P-450 interaction.

The NADPH-dependent reduction of rat hepatic microsomal cytochrome P-450 has been studied as a function of temperature. In the temperature range 4-37 degrees the reduction reaction was found to be biphasic and composed of two concurrent first order processes. This phenomenon was observed with microsomes from untreated and phenobarbital-induced animals in the presence or absence of exogenous Type I substrates. The amount of cytochrome P-450 reduced in the fast phase comprised approximately 70% of the total cytochrome P-450 at temperatures above 20 degrees. The temperature dependence of the fast phase was unusual for a membrane-bound enzyme system in that it lacked a discontinuity in the Arrhenius plot at a presumed phase transition temperature for the microsomal membrane. The slow phase of reduction behaved in a normal fashion for a membrane-bound enzyme system with a break in the Arrhenius plot at about 20 degrees. The data presented here combined with previous observations which include (a) the ratio of cytochrome P-450 to NADPH cytochrome P-450 reductase (NADPH:ferricytochrome oxidoreductase, EC 1.6.2.4) is 20:1, (b) the catalytic portion of the reductase molecule probably protrudes above the surface of the membrane, and (c) the cytochrome P-450 molecules are presumably embedded in the membrane support the hypothesis that the hepatic microsomal drug-metabolizing system exists as clusters with most of the cytochrome P-450 molecules arranged about a central reductase molecule. This central flavoprotein reductase is able to randomly reduce those cytochrome P-450 molecules within the cluster without translational motion through the microsomal membrane. The slow phase of reduction represents the reduction of those molecules not directly associated with the clusters.

Animals↗
PubMed1975

Kinetic studies on rat liver and beef heart mitochondrial ATPase. Evidence for nucleotide binding at separate regulatory and catalytic sites.

Mitochondrial ATPases from rat liver and beef heart were used to study the effects of guanylylimidodiphosphate (GMP-P(NH)P) and adenylylimidodiphosphate (AMP-P(NH)P) on the kinetics of MgATP, MgITP, and MgGTP hydrolysis. AMP-P(NH)P was a noncompetitive inhibitor of hydrolysis of all substrates with the rat liver enzyme, whether activating anions were present or not. Also with the liver enzyme, AMP-P(NH)P caused only MgATP hydrolysis to appear to have positive cooperativity. With the beef heart enzyme, AMP-P(NH)P was a competitive inhibitor of ATPase activity and caused positive cooperativity; it gave noncompetitive patterns with GTP or ITP as substrates. In both enzyme systems, GMP-P(NH)P gave complex inhibition patterns with MgATP as the substrate, but was a competitive inhibitor of MgITP and MgGTP hydrolysis. These results are interpreted as indicating the existence of two types of nucleotide binding sites, with varying degrees of specificity and interaction on the ATPase molecules from both sources. It is postulated that MgATP and AMP-P(NH)P bind to regulatory site while MgATP, MgGTP, Mgitp, and GMP-P(NH)P bind to the catalytic site.

Adenosine Triphosphatases↗