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Biomedical subjects

U Cogan

Publications and source records attributed to U Cogan.

At least 37 records · Page 2Linked to original sources
PubMed1989

Age and membrane fluidity.

Male rats aged 1, 9 and 19 months were used to study changes in membrane fluidity with age, employing the fluorescence polarization technique with 1,6-diphenyl-1,3,5-hexatriene (DPH) as the fluorescent probe. The intestinal microvillus membranes derived from the 19-month-old rats were found to possess lower fluidity than that observed with the membranes derived from the younger animals. The decrease in fluidity with age was also reflected in a corresponding increase in the gel-to-liquid crystalline transition temperature. Only small insignificant changes with age, were observed in the fluidity of the red blood cell membrane.

Aging↗
PubMed1989

The safety evaluation of Dunaliella bardawil as a potential food supplement.

The safety of the alga Dunaliella bardawil for food use, was evaluated in a multigeneration study with rats. Four generations were raised on diets containing 0, 5 or 10% dehydrated D. bardawil. Each experimental group comprised ten males and 20 females. No significant differences were observed between the rats consuming algae and the controls, of any generation, in general appearance, behaviour, growth, reproductive performance or gross pathology. The blood chemistry and haematology of the first generation animals, after 1 yr on the diets, showed no appreciable differences between the experimental and control animals. The only differences in histopathology observed were a decrease in some chronic inflammations and an increased frequency of focal bronchopneumonia in rats fed 10% algae compared with the controls. The latter effect may be attributed to the powdery nature of the algal diet. Considering the large amount of algae consumed by the experimental rats, and the absence of adverse effects in these animals, this multigeneration feeding study may be indicative of the safety of D. bardawil for human consumption.

Animal Feed↗
PubMed1989

The thermal properties of intestinal alkaline phosphatase of three kinds of deep-water fish.

1. The thermal properties of intestinal alkaline phosphatase were investigated with three species of deep-water fish in the temperature range of 0-70 C. 2. A relationship was found between the thermal stability of the enzyme and the fish origin. 3. Maximum activity of alkaline phosphatase of the fish that originated in tropical water, namely, Aphanopus carbo and Epigonus telescopus was 60 C, whereas the respective maximum enzyme activity of Etmopterus princeps that originated in the burial zone was 30 C. 4. A breakpoint at 10 degrees C in the Arrhenius plot of emzyme activity in the case of A. carbo and a lack of a break point in the case of E. telescopus and E. princeps, are in accordance with the stenothermic nature of the former and the everythermic nature of the two latter fish species.

Alkaline Phosphatase↗
PubMed1989

An effective method for plasma lipoprotein separation: studies of various animal species.

1. Plasma lipoprotein separation by density gradient ultracentrifugation largely depends on visual examination based on the natural yellow pigments of lipoproteins. 2. In non-human species and in humans with dyslipoproteinemia, some lipoproteins are not well visualized due to the lack of pigments. 3. Using a fluorescent probe in minute quantity (1,6 diphenyl-1,3,5-hexatriene) we were able to demonstrate an effective plasma lipoprotein separation using a discontinuous density gradient ultracentrifugation technique. 4. Plasma lipoproteins of human, chicken, rat and carp were compared showing the unique character of carp HDL.

Animals↗
PubMed1987

Protein malnutrition and the function and fluidity of the intestinal microvillus membrane in growing rats.

The effect of protein malnutrition on the function, fluidity and composition of the intestinal microvillus membrane was studied in growing rats. Weanling male rats were fed diets containing 10% protein derived from either wheat gluten (experimental diet) or casein (control diet). Intestinal microvillus membranes were isolated after a 7-wk feeding period. The functionality of the membranes, as assessed by the level of activity of the four enzymes alkaline phosphatase, gamma-glutamyl transpeptidase, leucine aminopeptidase and maltase, showed no difference between the membranes derived from the experimental and the control animals. Similar Arrhenius plot patterns of alkaline phosphatase activity (13-50 degrees C) and of the fluorescence anisotropy parameter (8-40 degrees C) were observed for both types of membranes with respect to the transition temperatures and energies of activation. In addition, the similarity between the membranes derived from the experimental and the control animals was also manifested in the cholesterol and phospholipid content. The study demonstrates that despite the extreme nutritional stress exerted on the gluten-fed rats, the integrity and functionality of the intestinal microvillus membrane was adequately maintained.

Alkaline Phosphatase↗
PubMed1983

Lipid fluidity of the individual hemileaflets of human erythrocyte membranes.

The impermeant fluorescent probes (MIMAR reagents) described here permit the assessment of the lipid fluidity of individual membrane hemileaflets. They should also prove useful for examining the outer hemileaflets of the plasma membranes of intact cells. The observations, thus far, that normal human erythrocyte membranes have a characteristic asymmetry of fluidity, with the outer leaflet more fluid, correspond to prior findings with Mycoplasma, Newcastle Disease viral envelopes, and mouse LM cells. Hence, it is possible that the pattern is quite general in biological membranes. The particular lipid and protein components of the human-erythrocyte membrane that underly the fluidity asymmetry are unknown. The increased content of phosphatidylcholine in the outer leaflet and of the anionic phospholipids in the inner leaflet would be consonant with the fluidity difference. On the other hand, sphingomyelin, which tends to decrease fluidity, is localized mainly in the outer leaflet. Unknown at present is whether the cholesterol content of the two leaflets differs. From the results reported above, it is tempting to speculate that exogenously added cholesterol tends to localize in the outer leaflet, normally the more fluid leaflet, whereas endogenous cholesterol is more readily removed from the inner leaflet. This suggests, but clearly does not establish, that in the normal erythrocyte the cholesterol content of the inner leaflet exceeds that of the outer. Lastly, integral membrane proteins are expected to decrease lipid fluidity, and the usual pattern seen on freeze-fracture of large numbers of intra-membranous particles on the cytoplasmic face may signify a greater influence of protein in the inner leaflet. The hypothesis that perturbations of the fluidity of a given hemileaflet influence the membrane proteins (and their associated functions) in that leaflet is well-supported by the evidence described above. On the other hand, we understand less well the mechanisms by which lipid fluidity influences the proteins. For example, the decrease in sulfhydryl group reactivity of spectrin, actin, and Band 3 owing to cholesterol depletion (Table 7) may be due to a physical displacement of these proteins, as suggested by Borochov and Shinitzky. Why then does the reactivity of glyceraldehyde-phosphate dehydrogenase sulfhydryl groups increase under these conditions? There remains much to learn about membrane molecular mechanics and lipid-protein interactions. In such studies the impermeant MIMAR probes described here should prove useful.

Acanthocytes↗
PubMed1982

Asymmetry of lipid dynamics in human erythrocyte membranes studied with permanent fluorophores.

The fluorescence anisotropy and mean excited-state lifetime of 1,6-diphenyl-1,3,5-hexatriene, 12-(9-anthroyloxy)stearate, 2-(9-anthroyloxy)stearate, and pyrenedecanoic acid in the membranes of intact human erythrocytes, lysate suspensions, and ghost membranes were compared. The excited-state lifetime of each lipid fluorophore, estimated by single photon counting, is significantly shorter in the intact erythrocytes as compared to the lysates, owing to nonradiative energy transfer from the lipid fluorophore donors in the membrane to heme acceptors at the endothelial surface of the intact cell. The fluorescence observed in intact cell suspensions is thus weighted in favor of outer leaflet fluorophores, and estimates of the fluorescence anisotropy by steady-state fluorescence polarization indicate that all four fluorescent probes experience greater motional freedom in the outer as compared to the inner membrane leaflet. The results are in accord with prior studies of impermeant pyrene derivatives, which also indicate that the outer leaflet lipids have greater motional freedom.

Cell-Free System↗
PubMed1981

Asymmetry of lipid dynamics in human erythrocyte membranes studied with impermeant fluorophores.

The synthesis, purification, and application of five membrane-impermeant derivatives of pyrene are described. Each probe consists of a membrane-impermeant moiety, either an oligosaccharide or glutathione, linked to pyrene via a connecting arm. Intact human erythrocytes and leaky ghost membranes prepared from them were treated with the probes to label, respectively, the outer membrane leaflet and both leaflets. Motional freedom of the pyrene fluorophores in the membrane was assessed by estimation of the steady-state polarization of fluorescence, the excited-state lifetime, and the excimer/monomer fluorescence intensity ratio. The fluorescence anisotropy of each impermeant derivative was lower in the outer as compared to the inner hemileaflet, whereas the corresponding excited-state lifetimes were similar. Excimer formation was consistently greater in the outer leaflet. The results demonstrate that the impermeant fluorophores experience greater motional freedom ("fluidity") in lipid domains of the outer as compared to the inner leaflet of the human erythrocyte membrane.

Erythrocyte Membrane↗
PubMed1976

Comparative studies of human and chicken retinol-binding proteins and prealbumins.

Microheterogeneity of retinol-binding proteins of human plasma and urine, and of chicken plasma was studied by polyacrylamide gel electrophoresis. All three protein systems were found microheterogenous. Incorporation of retinol into the protein preparations on the one hand, and depletion of these proteins from retinol on the other hand, enabled us to clarify the extent to which the presence or absence of the ligand affects the apparent heterogeneity. Upon electrophoresis, each of the native proteins displayed two pairs of protein zones. It appeared that within each pair the fast moving band corresponded to aporetinol-binding protein which upon binding of retinol was converted to a holoprotein with a slightly lower mobility. However, it did not seem that proteins of one pair were converted to proteins of the second pair upon binding of retinol, substantiating ghe microheterogenous character of this protein system. A rapid, two step procedure for isolation of prealbumins from plasma is described. The method which consists of DEAE-cellulose chromatography follwed by preparative electrophoresis was utilized to separate human and chicken prealbumins. Routine dodecyl sulphate electrophoresis resulted in partial dissociation of human prealbumin but in no dissociation of the chicken protein. More drastic treatments prior to electrophoresis were needed to effect complete disruption of both proteins into subunits.

Animals↗
PubMed1976

The interaction between retinol-binding proteins and prealbumins studied by fluorescence polarization.

The interaction between retinol-binding proteins and prealbumins of human and chicken was studied by fluorescence polarization techniques. The binding affinity between chicken plasma retinol-binding protein and chicken prealbumin was essentially the same as between the respective human proteins. Human urine retinol-binding protein displayed a similar affinity, though possibly slightly smaller than that of the human plasma protein, toward human prealbumin. Retinol-binding proteins and prealbumins of human and chicken have been found to cross-interact displaying an affinity similar to that displayed by the proteins of the same species. Solution of a binding equation which assumes identical, independent sites, indicated that the number of binding sites on prealbumin for retinol-binding protein is somewhat less than 2 with the human system, and in the neighborhood of 4 with the chicken system. A possible interpretation suggests that prealbumin possesses four identical binding sites for retinol-binding protein, one for each subunit, but that the binding is of a negative cooperative nature. A major share of the negative cooperativity is likely to result from steric hindrance induced by already bound retinol-binding protein molecules, which have a sizable volume compared to the volume of the prealbumin molecule. The cooperativity is likely to be more pronounced with the human system. Rotational relaxation times derived from Perrin plots suggest that 1:1 molecular complexes of retinol-binding proteins with prealbumins have a compact structure.

Animals↗
PubMed1976

Binding affinities of retinol and related compounds to retinol binding proteins.

Fluorimetric titrations were used to determine apparent dissociation constants of the all-trans isomers of retinol, retinoic acid, retinyl acetate and retinyl palmitate to human-retinol binding protein and chicken-retinol binding protein. Enhancement of the fluorescence of retinol and retinyl acetate when bound to the protein was utilized to establish the binding affinity of these compounds. With retinoic acid which is essentially a non-fluorescent compound, quenching of protein fluorescence due to energy transfer to the bound ligand from tryptophanyl residues served to determine the binding affinity. The various ligands display 1:1 molecular complexes with both types of retinol binding proteins. Retinol, retinoic acid and retinyl acetate were found to have similar binding affinities to both species of carrier proteins: For retinol K'd=1.9 X 10(-7) M with human-retinol binding protein and K'd=1.5 X 10(-7) M with chicken-retinol binding protein; for retinoic acid K'd-2.1 X 10(-7) M with human-retinol binding protein; for retinyl acetate and K'd=2.2 X 10(-7) M with chicken-retinol binding protein; for retinyl acetate K'd=2.2 X 10(-7) M with human-retinol binding protein and K'd=1.7 X 10(-7) M with chicken-retinol binding protein. Retinyl palmitate appeared to have weak association with either of the two retinol binding proteins, if at all. The above results suggest that both human and chicken retinol binding proteins behave similar with respect to the binding of the ligands. Non-polar interactions probably play a primary role in the binding and effects of functional groups and charges are of secondary importance.

Animals↗