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J R Lancaster

Publications and source records attributed to J R Lancaster.

At least 73 records · Page 4Linked to original sources
PubMed1989

Sodium, protons, and energy coupling in the methanogenic bacteria.

In this review, I focus on the bioenergetics of the methanogenic bacteria, with particular attention directed to the roles of transmembrane electrochemical gradients of sodium and proton. In addition, the mechanism of coupling ATP synthesis to methanogenic electron transfer is addressed. Evidence is reviewed which suggests that the methanogens possess great diversity in their bioenergetic machinery. In particular, in some methanogens the primary ion which is translocated coupled to metabolic energy is the proton, while others appear to utilize sodium. In addition, ATP synthesis driven by methanogenic electron transfer is accomplished in some organisms by a chemiosmotic mechanism and is coupled by a more direct mechanism in others. A possible explanation for this diversity (which is consistent with the relatedness of these organisms to each other and to other members of the Archaebacteria as determined by molecular biological techniques) is discussed.

Bacteria↗
PubMed1988

Iron-sulfur centers involved in methanogenic electron transfer in Methanobacterium thermoautotrophicum (delta-H).

Utilizing a subcellular particulate preparation from Methanobacterium thermoautotrophicum (delta-H) which contains all detectable methanogenic electron transfer activity, we present the results of the effects of the anaerobic addition of oxidized factor F420 and of methyl coenzyme M plus ATP on the EPR signals from reduced iron-sulfur centers and a rapidly-relaxing radical species. Based on these results, we report the existence of a minimum of three iron-sulfur centers which are capable of donating electrons to these cofactors.

Anaerobiosis↗
PubMed1988

Upper gastrointestinal bleeding.

Bleeding in the upper gastrointestinal tract is a problem that confronts all physicians involved in primary patient care. It continues as one of the most common acute medical management problems, leads to substantial morbidity and mortality, and presents both diagnostic and therapeutic challenges to the physician. The purpose of this paper is to provide an overview of the common causes of upper gastrointestinal bleeding and to discuss initial assessment, diagnosis, management, and, where possible, prevention.

Esophageal and Gastric Varices↗
PubMed1985

Electron transfer-driven ATP synthesis in Methanococcus voltae is not dependent on a proton electrochemical gradient.

Intracellular ATP levels in whole cells of Methanococcus voltae respond to electron transfer coupled to methanogenesis. ATP synthesis can also be induced by an artificially imposed transmembrane electrical potential [formed by electrogenic movement outwards of potassium (induced by valinomycin) or of protons (induced by an uncoupler], or by a pH gradient (acid outside). These results implicate the existence of a reversible ATPase coupled to electrogenic movement of an ion(s) other than potassium or proton, and that ionophores are competent to catalyze ion movement across the cytoplasmic membrane of this organism (which is the sole membrane structure in this species). ATP synthesis driven by electron transfer is, however, insensitive to the addition of such ionophores. These results indicate that although cells possess an ion-translocating ATPase (possibly involved in the maintenance of internal ionic composition homeostasis), methanogenesis-driven ATP synthesis does not involve the intermediacy of a transmembrane ion gradient. Primarily because methane formation has been previously demonstrated to involve true electron transfer, substrate-level phosphorylation (at least in analogy to other systems) has been generally ruled out. The results presented here suggest that at least one methanogenic bacterium may use a direct linkage of ATP synthesis to electron transfer.

Journal Article↗
PubMed1985

Hemosuccus pancreaticus. An unusual cause of upper gastrointestinal bleeding.

Two cases of hemosuccus pancreaticus as the source of upper gastrointestinal bleeding of unknown cause are presented. The literature on this rare cause of gastrointestinal blood loss is reviewed. Also, the influences of time-course and clinical appearance on the diagnosis of this problem are described.

Aneurysm↗
PubMed1983

Nitrite inhibition of Clostridium botulinum: electron spin resonance detection of iron-nitric oxide complexes.

Vegetative cells of Clostridium botulinum were shown to contain iron-sulfur proteins that react with added nitrite to form iron-nitric oxide complexes, with resultant destruction of the iron-sulfur cluster. Inactivation of iron-sulfur enzymes (especially ferredoxin) by binding of nitric oxide would almost certainly inhibit growth, and thus is probably the mechanism of botulinal inhibition by nitrite in foods.

Clostridium botulinum↗
PubMed1982

Mechanism of lactose-proton cotransport in Escherichia coli. Kinetic results in terms of the site exposure model.

Rigorous kinetic derivations are presented for the Site Exposure mechanism of lactose-proton cotransport in E. coli [J. Theor. Biol. (1978) 75, 35-50]. Proton translocation inwards is solely associated with the external exposure of the galactoside binding site. A symmetric dimer configuration of the transporter is proposed, resulting in two forms corresponding to the cis and the trans orientation of the binding sites. The cis to trans orientation is inherently unfavorable, induced only by transmembrane substrate gradients. Recently reported extensive kinetic data are straightforwardly predicted by this mechanism, including the complicated effects on the apparent affinity and maximal velocity of uptake exhibited by changes in the magnitude of the proton electrochemical gradient.

Escherichia coli↗
PubMed1982

Siderophore iron transport followed by electron paramagnetic resonance spectroscopy.

Siderophore iron transport was followed in Ustilago sphaerogena using isotope transport assays coupled with EPR spectroscopy. EPR spectroscopy was used as a quantitative tool to follow the rate of reduction of siderophore iron(III) to iron(II) in the cell suspension by following the disappearance of the signal at g = 4.3. This rate was compared with the rate of iron transport, measured by the disappearance of radioactively labeled iron from the medium. The transport of three iron chelates was examined: the ferric siderophores ferrichrome and ferichrome A, and iron(III) chelated to excess citrate. For the transport of ferrichrome, an iron(III) ionophore, the rate of reduction of iron(III) to iron(II) was significantly lower than the rate of uptake of isotope from the medium supernatant, which is consistent with the established mechanism of uptake of the entire complex followed by intracellular reduction to remove the iron from the ligand. However, the rate of reduction of ferrichrome A, a non-ionophore, was identical with the rate of transport of iron into the cell. Iron(III) citrate was reduced at a rate slightly lower than the rate of transport. These data suggest that reduction of iron(III) is involved in the transport of iron from ferichrome A and possibly from iron(III) citrate.

Biological Transport, Active↗
PubMed1982

Steroidogenic electron transport in adrenal cortex mitochondria.

The flavoprotein NADPH-adrenodoxin reductase and the iron sulfur protein adrenodoxin function as a short electron transport chain which donates electrons one-at-a-time to adrenal cortex mitochondrial cytochromes P-450. The soluble adrenodoxin acts as a mobile one-electron shuttle, forming a complex first with NADPH-reduced adrenodoxin reductase from which it accepts an electron, then dissociating, and finally reassociating with and donating an electron to the membrane-bound cytochrome P-450 (Fig. 9). Dissociation and reassociation with flavoprotein then allows a second cycle of electron transfers. A complex set of factors govern the sequential protein-protein interactions which comprise this adrenodoxin shuttle mechanism; among these factors, reduction of the iron sulfur center by the flavin weakens the adrenodoxin-adrenodoxin reductase interaction, thus promoting dissociation of this complex to yield free reduced adrenodoxin. Substrate (cholesterol) binding to cytochrome P-450scc both promotes the binding of the free adrenodoxin to the cytochrome, and alters the oxidation-reduction potential of the heme so as to favor reduction by adrenodoxin. The cholesterol binding site on cytochrome P-450scc appears to be in direct communication with the hydrophobic phospholipid milieu in which this substrate is dissolved. Specific effects of both phospholipid headgroups and fatty acyl side-chains regulate the interaction of cholesterol with its binding side. Cardiolipin is an extremely potent positive effector for cholesterol binding, and evidence supports the existence of a specific effector lipid binding site on cytochrome P.450scc to which this phospholipid binds.

Adrenal Cortex↗
PubMed1982

Multilocular cysts of the peritoneum.

Multilocular cysts of the peritoneum diagnosed at the Mayo Clinic from 1907 through 1981 were examined and divided, on the basis of their light microscopic features, into two groups--cystic mesotheliomas and cystic lymphangiomas. There are apparent clinical differences between the two groups. Cystic mesotheliomas tend to occur in adult females and often recur. Cystic lymphangiomas occur most often in males, often develop in children, and rarely recur, if at all. The distinguishing histologic features are the cytologic characteristics of the cells lining the cysts and the presence or absence of smooth muscle in the wall of the cysts.

Adolescent↗
PubMed1979

Participation of the membrane in the side chain cleavage of cholesterol. Reconstitution of cytochrome P-450scc into phospholipid vesicles.

Cytochrome P-450scc can be reconstituted into a phospholipid bilayer in the absence of added detergent by incubation of purified hemoprotein with preformed phosphatidylcholine vesicles. Salt effects demonstrate that the primary interaction between the cytochrome and phospholipid vesicles is hydrophobic rather than ionic; in contrast, neither adrenodoxin reductase nor adrenodoxin will bind to phosphatidylcholine vesicles by hydrophobic interactions. Insertion of cytochrome P-450scc into a phospholipid bilayer results in conversion of the optical spectrum to a low spin type, but this transition is markedly diminished if cholesterol is incorporated within the bilayer. Vesicle-reconstituted cytochrome P-450scc metabolizes cholesterol within the bilayer (turnover = 13 nmol/min/nmol of cytochrome P-450scc); virtually all (greater than 94%) of the cholesterol within the vesicle is accessible to the enzyme. "Dilution" of cholesterol within the bilayer by increasing the phospholipid/cholesterol ratio at a constant amount of cholesterol and cytochrome P-450scc results in a decreased rate of side chain cleavage, and cytochrome P-450scc incorporated into a cholesterol-free vesicle cannot metabolize cholesterol within a separate vesicle. In addition, activity of the reconstituted hemoprotein is sensitive to the fatty acid composition of the phospholipid. These results indicate that the cholesterol binding site on vesicle-reconstituted cytochrome P-450scc is in communication with the hydrophobic bilayer of the membrane. The reducibility of vesicle-reconstituted cytochrome P-450scc as well as spectrophotometric and activity titration experiments show that all of the reconstituted cytochrome P-450scc molecules possess an adrenodoxin binding site which is accessible from the exterior of the vesicle. Activity titrations with adrenodoxin reductase also demonstrate that a ternary or quaternary complex among adrenodoxin reductase, adrenodoxin, and cytochrome P-450scc is not required for catalysis, a finding consistent with our proposed mechanism of steroidogenic electron transport in which adrenodoxin acts as a mobile electron shuttle between adrenodoxin reductase and cytochrome P-450 (Lambeth, J.D., Seybert, D.W., and Kamin, H. (1979) J. Biol. Chem. 254, 7255-7264.

Adrenal Cortex↗
PubMed1979

Identification of the iron-sulfur center of spinach ferredoxin-nitrite reductase as a tetranuclear center, and preliminary EPR studies of mechanism.

EPR spectroscopic and chemical analyses of spinach nitrite reductase show that the enzyme contains one reducible iron-sulfur center, and one site for binding either cyanide or nitrite, per siroheme. The heme is nearly all in the high spin ferric state in the enzyme as isolated. The extinction coefficient of the enzyme has been revised to E386 = 7.6 X 10(4) cm-1 (M heme)-1. The iron-sulfur center is reduced with difficulty by agents such as reduced methyl viologen (equilibrated with 1 atm of H2 at pH 7.7 in the presence of hydrogenase) or dithionite. Complexation of the enzyme with CO (a known ligand for nitrite reductase heme) markedly increases the reducibility of the iron-sulfur center. New chemical analyses and reinterpretation of previous data show that the enzyme contains 6 mol of iron and 4 mol of acid-labile S2-/mol of siroheme. The EPR spectrum of reduced nitrite reductase in 80% dimethyl sulfoxide establishes clearly that the enzyme contains a tetranuclear iron-sulfur (Fe4S4) center. The ferriheme and Fe4S4 centers are reduced at similar rates (k = 3 to 4 s-1) by dithionite. The dithionite-reduced Fe4S4 center is rapidly (k = 100 s-1) reoxidized by nitrite. These results indicate a role for the Fe4S4 center in catalysis.

Dithionite↗
PubMed1977

Studies of the beta-galactoside transporter in inverted membrane vesicles of Escherichia coli. I. Symmetrical facilitated diffusion and proton gradient-coupled transport.

Facilitated diffusion of [14C]lactose into inverted membrane vesicles of Escherichia coli was measured using HgCl2 as a stopping reagent and polylysine to flocculate the vesicles for filtration. Equilibration of lactose between the internal and external volumes required expression of the y gene of the lac operon and was inhibited by thiodigalactoside or by prior incubation with N-ethylmaleimde or HgCl2. The initial rate of uptake was saturable, with a Kt of 0.95 mM. Counterflow of [14C]lactose was demonstrated in either direction. ATP hydrolysis or respiration drove the efflux of internal lactose. The effect of ATP required addition of F1 coupling factor (ATPase) from E. coli when lactose transport was studied in F1-deficient inverted vesicles. Accumulation of lactose against a concentration gradient was achieved by forming an artificial electrochemical proton gradient consisting of a membrane potential negative inside or a pH gradient basic inside. Addition of ATP inhibited this proton driven uptake showing that it occurred in inverted vesicles. It was concluded that the lactose-proton co-transport protein (M protein) is qualitatively symmetrical with respect to the facilitated diffusion of lactose and the coupling of proton and lactose transport.

Biological Transport↗