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Biomedical subjects

J van Steveninck

Publications and source records attributed to J van Steveninck.

At least 37 records · Page 2Linked to original sources
PubMed1980

Temperature dependence of photodynamic red cell membrane damage.

1. The protoporphyrin-sensitized photo-oxidation of free amino acids, amino acid residues in solubilized spectrin and amino acid residues in red blood cell membranes appeared to be virtually independent of temperature over the range 0-37 degrees C. The photodynamically produced increase in cation permeability in intact cells was also almost temperature independent. 2. The photodynamic cross-linking of the membrane proteins, on the other hand, was clearly temperature dependent, both when the proteins were present in the membrane structure and when isolated and purified. 3. With red cell membranes, illuminated in the presence of protoporphyrin at 0 degrees C, it could be shown that during subsequent incubation in the dark at 37 degrees C the protein cross-linking increased considerably. 4. The results indicate that cross-linking of membrane proteins is a secondary reaction in which rather stable photo-oxidation products of susceptible amino acid residues are involved. Furthermore, these experiments strongly suggest that the deterioration of membrane function, leading to increased caption permeability, is caused by photo-oxidation of amino acid residues rather than by cross-linking of membrane proteins.

Erythrocyte Membrane↗
PubMed1979

Hypertonic cryohemolysis of human red blood cells.

Hypertonic cryohemolysis of human erythrocytes is caused by incubation of the cells in hypertonic medium at a temperature of 20--50 degrees C (stage 1), with subsequent cooling to 0 degrees C (stage 2). In 0.86 M sucrose hemolysis increases, with increasing stage 1 temperature, whereas in 1 M NaCl cryohemolysis has a temperature optimum at a stage 1 temperature of about 30 degrees C. Cryohmeolysis is inhibited by preceding ATP depletion of the cells and by preincubation of the cells in hypertonic medium at 0 degrees C. In general, anesthetics inhibit cryohemolysis strongly. Only in 1 M NaCl at stage 1 temperatures in the range of 40--50 degrees C is cryohemolysis stimulated by these drugs, if present during the entire incubation period. This effect is abolished, however, when the anesthetic is added after prior incubation of the cells at 40--50 degrees C in 1 M NaCl. Ghost-bound ANS fluorescence indicates complicated conformation changes in the membrane structure during the various experimental stages leading to cryohemolysis. Some of the experimental results can be considered as examples of molecular hysteresis, thus indicating several different metastable structures of the membrane, under various experimental conditions. The described results support the working hypothesis of Green and Jung that the experimental procedure results in membrane protein damage, preventing normal adaptation of the membrane during cooling.

Adenosine Triphosphate↗
PubMed1978

Photodynamic effects of protoporphyrin on human erythrocytes. Nature of the cross-linking of membrane proteins.

Protoporphyrin-sensitized photooxidation in human red blood cell membranes leads to severe deterioration of membrane structure and function. The membrane damage is caused by direct oxidation of amino acid residues, with subsequent cross-linking of membrane proteins. The chemical nature of these cross-links was studied in model systems, isolated spectrin and red cell ghosts. Cysteine and methionine are not involved in the cross-linking reaction. Further it could be shown that dityrosine formation, the crucial mechanism in oxidative cross-linking of proteins by peroxidase-H2O2 treatment, plays no role in photodynamic cross-linking. Experimental evidence indicated that a secondary reaction between free amino groups and a photooxidation product of histidine, tyrosine or tryptophan is involved in photodynamic cross-linking. This was deduced from the reaction observed between compounds containing a free amino group and photooxidation products of these amino acids, both in model systems, isolated spectrin and erythrocyte ghosts. In accordance, succinylation of free amino groups of membrane proteins or addition of compounds with free amino groups protected against cross-linking. Quantitative data and consideration of the reaction mechanisms of photodynamic oxidation of amino acids make it highly probable that an oxidation product of histidine rather than of tyrosine or tryptophan is involved in the cross-linking reaction, via a nucleophilic addition by free amino groups.

Amino Acids↗
PubMed1978

Erythrocyte membrane studies in familial hypokalemic periodic paralysis.

A study of RBC membrane functions was performed in four patients suffering from familial hypokalemic periodic paralysis who had permanent muscular weakness. Electrophoretograms of membrane proteins, cell deformability, calcium-promoted potassium efflux, calcium-ATPase activity, and endogeneous phosphorylation of membrane proteins were all within the normal range. These results are compared with similar studies performed in myotonic and Duchenne-type dystrophies, in which abnormalities in the RBC membrane have been described. The results do not support the theory of RBC involvement in hypokalemic periodic paralysis. However, this does not imply that the muscle cell membrane is not involved in the underlying pathological processes in this disorder.

Adenosine Triphosphatases↗
PubMed1977

Active transport of L-sorbose and 2-deoxy-D-galactose in Saccharomyces fragilis.

Sorbose and 2-deoxy-D-galactose are taken up in Saccharomyces fragilis by an active transport mechanism, as indicated by the energy requirement of the process and the accumulation of free sugar against the concentration gradient. There are no indications for transport-associated phosphorylation as mechanism of energy coupling with these two sugars. The measured sugar-proton cotransport and the influx inhibition by uncouplers suggest a chemiosmotic coupling mechanism. Thus there are at least two different active transport mechanisms operative in Saccharomyces fragilis: transport-associated phosphorylation in the case of 2-deoxy-D-glucose and chemiosmotic coupling in the case of sorbose and 2-deoxy-D-galactose. The differences between the two mechanisms are discussed. Uncouplers do not stimulate downhill sorbose transport in energy-depleted cells and evoke an almost complete inhibition of efflux and of exchange transport. The differences between this sugar-proton cotransport system and similar systems in bacteria and Chlorella are discussed.

Adenosine Triphosphate↗
PubMed1977

Binding of Protoporphyrin to hemoglobin in red blood cells of patients with erythropoietic protoporphyria.

Virtually all protoporphyrin in erythrocytes of patients with erythropoietic protoporphyria is bound to hemoglobin. The maximum of the fluorescence excitation spectrum of this protoporphyrin-hemoglobin complex shifted, with increasing concentration, from 405 nm to 389 nm. A similar shift was observed when titrating a solution of free protoporphyrin with hemoglobin. The Soret maximum of free protoporphyrin itself, on the other hand, was not concentration-dependent. These observations indicate that spectrofluorometric measurements do not allow conclusions concerning the mode of protoporphyrin binding to hemoglobin. Experiments on protoporphyrin exchange between the hemoglobins A, F and S reinforced the previously drawn conclusion that protoporphyrin is bound to hemoglobin at the heme-binding sites.

Binding Sites↗
PubMed1976

Photodynamic modification of proteins in human red blood cell membranes, induced by protoporphyrin.

Illumination of erythrocytes or erythrocyte membranes with visible light in the presence of protoporphyrin causes photodynamic damage of the cell membrane. This process is reflected a.o. by a mutilated ultrastructure and changes of the physical properties of the membrane proteins. Illumination in the presence of protoporphyrin causes association of membrane proteins, leading to blurring of the protein bands in electropheretograms, disappearance of bands and the appearance of protein aggregates on top of the gels. The formation of large protein aggregates is also indicated by Sephadex gel filtration of the solubilized membrane proteins. In kinetic studies it appeared that spectrin and the bands 2.1, 2.2, 2.3 and 6 are most susceptible and that band 3 is least susceptible to this cross-linking reaction. Experimental results indicate that this cross-linking is caused by direct photooxidation of membrane proteins. Peroxidation of unsaturated fatty acids is not involved in the process. The significance of this process for studies on membrane structure and on photodynamic membrane damage is discussed.

Blood Protein Electrophoresis↗
PubMed1975

Transport-associated phosphorylation of 2-deoxy-D-glucose in Saccharomyces fragilis.

2-Deoxy-D-glucose transport and metabolism was studied in Saccharomyces fragilis. Inside the cells four phosphorylated and three non-phosphorylated derivatives were found and identified. Accumulation of phosphorylated 2-deoxyglucose derivatives was balanced by a concomitant decrease of cellular ATP, orthophosphate and polyphosphates. The free sugar was concentrated against a concentration gradient, contradiciting facilitated diffusion. Pulse labeling experiments revealed transport-associated phosphorylation. Theoretical considerations and analysis of the effects of iodoacetate showed that an intracellular hexokinase activity was not involved in 2-deoxyglucose phosphorylation, although this sugar is a good substrate for the enzyme in in vitro experiments.

Adenosine Triphosphate↗
PubMed1975

Decreased haem synthetase activity in blood cells of patients with erythropoietic protoporphyria.

A constant finding in erythropoietic protoporphyria (E.P.P.) is a raised protoporphyrin content of the erythrocytes. It has been shown before that the biosynthesis of this protoporphyrin takes place in the erythroid cell. In circulating blood cells of patients with E.P.P. the haem synthetase activity is significantly decreased. This observation and the increased protoporphyrin concentration in the cells can be explained by assuming a decreased stability of haem synthetase in the red blood cells of E.P.P. patients.

Erythrocytes↗