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Biomedical subjects

K van Dam

Publications and source records attributed to K van Dam.

At least 73 records · Page 4Linked to original sources
PubMed1981

The residual protonmotive force in mitochondria after an oxygen pulse.

Both from irreversible thermodynamics and from mass-action kinetics it can be derived that upon anaerobiosis in an oxygen-pulse experiment the protonmotive force across a mitochondrial membrane undergoes a sudden drop. Under representative conditions the protonmotive force after the drop (the residual protonmotive force) is shown to be less than 3 kJ . mol-1 as opposed to steady-state values for the protonmotive force of 19 kJ . mol-1. It is concluded that correction for proton leakage in pulse experiments by back extrapolation underestimate proton leakage. Consequently the observed H+/O stoichiometries must underestimate the true H+/O ratios.

Hydrogen-Ion Concentration↗
PubMed1981

Amino acid-dependent sodium transport in plasma membrane vesicles from rat liver.

The L-alanine-dependent transport of sodium ions across the plasma membrane of rat-liver parenchymal cells was studied using isolated plasma membrane vesicles. Sodium uptake is stimulated specifically by the L-isomer of alanine and other amino acids, whose transport is sodium-dependent in rat-liver plasma membrane vesicles. The L-alanine-dependent sodium flux across the membrane is inhibited by an excess of Li+ ions, but not by K+ or choline ions. Sodium transport is sensitive to -SH reagents and ionophores, and is an electrogenic process: a membrane potential (negative inside) can enhance L-alanine-dependent sodium accumulation. The data presented provide further evidence for a sodium-alanine cotransport mechanism.

Alanine↗
PubMed1981

The influence of asymmetrically distributed Ca2 on Na permeability of bovine brain phospholipid liposomes.

Liposomes prepared from bovine brain phospholipids in the absence of Ca2 spontaneously capture Na from the outside medium down a concentration gradient. When the Na concentration gradient is not yet completely equilibrated, addition of Ca2 causes an apparent efflux of Na against this gradient. This efflux cannot exclusively be ascribed to increased permeability as a consequence of asymmetrical distribution of Ca2. Another mechanism, for example lysis of the liposomes, must be involved. Liposomes prepared from bovine brain phospholipids in the presence of 3.5 mM Ca2 do not capture Na spontaneously. Removal of Ca2 on the outside by adding EDTA, inducing asymmetrical distribution of Ca2 in this way, provides for an influx of Na into the liposomes down a concentration gradient.

Animals↗
PubMed1980

Heterogeneous distribution of the sodium-dependent alanine transport activity in the rat hepatocyte plasma membrane.

The localization of the sodium-dependent alanine uptake activity in rat liver cells was studied. Fractions representative of the canalicular, the contiguous (lateral) and the blood-sinusoidal surface of the hepatocyte were isolated by means of centrifugal fractionation and density gradient centrifugation. The distribution of various marker-enzyme activities in conjunction with the occurrence of alanine transport activity was studied both in fractions obtained after zonal density gradient centrifugation, and in the subcellular fractions mentioned above. It is concluded that the sodium-dependent alanine transport activity is primarily located in the blood-sinusoidal plasma membrane of the hepatocyte.

Alanine↗
PubMed1979

Association of bacteriorhodopsin with lipid-impregnated filters. Evidence for fusion of bacteriorhodopsin-containing vesicles with the lipid phase of the filter.

Bacteriorhodopsin vesicles were associated with cellulose-nitrate filters impregnated with a solution of phospholipids in hexadecane. The generation of (photo)potentials upon illumination of the filter was studied in the absence and presence of ionophores, phospholipase A2, EDTA or polyene antibiotics. From these experiments the following conclusions are drawn. 1. Upon illumination of the filter, bacteriorhodopsin pumps protons into aqueous compartments located in the filter. 2. These aqueous compartments possibly do not originate from the compartments enclosed by the bacteriorhodopsin vesicles. Evidence is obtained that aqueous compartments are present in the surface layers of the lipid-impregnated filters. 3. The results are explained most easily by a mechanism, whereby fusion occurs between the vesicles and the lipids of the filter.

Amphotericin B↗
PubMed1978

Na+-dependent methyl beta-thiogalactoside transport in Salmonella typhimurium.

We have studied the role of sodium ions in methyl beta-thiogalactoside (TMG) transport via the melibiose permease (TMG II) in Salmonella typhimurium. TMG uptake via TMG II in anaerobic, straved and metabolically poisoned cells is dependent on an inward-directed Na+ gradient. Cells which have been partially depleted of endogenous substrates show H+ extrusion upon sodium-stimulated TMG influx. Measurements of the electrochemical H+ gradient in cells, starved in different ways for endogenous substrates, suggest that this proton extrusion is probably not linked to the actual translocation mechanism but is the result of metabolism induced by TMG plug Na+ uptake.

Biological Transport↗
PubMed1978

Bacteriorhodopsin vesicles. An outline of the requirements for light-dependent H+ pumping.

A systematic study was performed to determine under which conditions bacteriorhodopsin can be applied as an energy generator in reconstituted systems. It is concluded that reconstitution of an active light-driven proton pump is possible over a wide range of conditions. High extents (per bacteriorhodopsin molecule) of proton uptake by reconstituted vesicles are found at a high lipid to protein ratio, after long sonication and at high pH. No active proton pump is obtained if reconstitution is attempted at high pH with neutral phospholipids or at low ionic strength with negatively charged lipids. Attention was also paid to the requirement of a crystalline array for active pumping; most likely, monomeric bacteriorhodopsin molecules can effectively pump protons.

Bacteriorhodopsins↗
PubMed1978

Sodium-dependent alanine transport in plasma-membrane vesicles from rat liver.

L-Alanine transport was studied in plasma-membrane vesicles from rat liver. A gradient of NaSCN, but not of KSCN, stimulated alanine uptake. Monensin plus carbonyl cyanide p-trifluoromethoxyphenylhydrazone abolished the observed overshoot in uptake. After equilibration of alanine, NaSCN induced uphill transport.

Alanine↗
PubMed1978

Specific labelling of the (Ca2+ + Mg2+)-ATPase of Escherichia coli with 8-azido-ATP and 4-chloro-7-nitrobenzofurazan.

1. 8-Azido-ATP is a substrate for Escherichia coli (Ca2+ + Mg2+)-ATPase (E. coli F1). 2. Illumination of E. coli F1 in the presence of 8-azido-ATP causes inhibition of ATPase activity. The presence of ATP during illumination prevents inhibition. 3. 8-Azido-ATP and 4-chloro-7-nitrobenzofurazan (NbfCl) bind predominantly to the alpha subunit of the enzyme, but also significantly to the beta subunit. 4. The alpha subunit of E. coli F1 seems to have some properties that in other F1-ATPases are associated with the beta subunit.

4-Chloro-7-nitrobenzofurazan↗
PubMed1977

Leigh's encephalomyelopathy in a patient with cytochrome c oxidase deficiency in muscle tissue.

A patient is described with subacute necrotizing encephalomyelopathy proven by autopsy. A slight increase of blood pyruvate and lactate levels with an increased lactate/pyruvate ratio and frequently increased beta-hydroxybutyrate/acetoacetate ratio suggested a disorder of mitochondrial oxidation. A cytochrome c oxidase deficiency was shown in peripheral muscle tissue with some residual cytochrome c oxidase activity in heart muscle. Normal cytochrome c oxidase activity was present in liver tissue. Because of the markedly higher levels of pyruvate and lactate in CSF compared with blood and an increased lactate/pyruvate ratio in CSF, there may also have been defective activity of cytochrome c oxidase in brain tissue. After a period of apparently normal development, the child's clinical condition gradually deteriorated and she died at age 6 years due to respiratory insufficiency. This study illustrates the fact that Leigh's disease is not linked to a single inherited molecular defect.

Acetoacetates↗
PubMed1975

Control of choline oxidation by rat-liver mitochondria.

The steady-state concentrations of choline and its reaction products in intact rat-liver mitochondria were determined under different conditions. From these measurements, it is concluded that in a sucrose medium choline dehydrogenation and betaine aldehyde dehydrogenation are the rate-limiting steps in overall choline oxidation under "State-3" or uncoupled conditions, respectively. Ageing of the mitochondria leads to changes in the mitochondrial membrane, resulting in a markedly different pattern of oxidation products. This finding explains why rotenone inhibits oxygen uptake with choline as substrate in fresh but not in aged mitochondria.

Acetoacetates↗