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Biomedical subjects

C Long

Publications and source records attributed to C Long.

At least 145 records · Page 8Linked to original sources
PubMed1971

The binding of calcium ions by erythrocytes and 'ghost' -cell membranes.

1. Washed human erythrocytes, suspended in iso-osmotic sucrose containing 2.5mm-calcium chloride, bind about 400mug-atoms of calcium/litre of packed cells. Sucrose may be replaced by other sugars. 2. Partial replacement of sucrose by iso-osmotic potassium chloride diminishes the uptake of calcium, 50% inhibition occurring at about 50mm-potassium chloride. 3. Other univalent cations behave like potassium, whereas bivalent cations are much more inhibitory. The tervalent cations, yttrium and lanthanum, however, are the most effective inhibitors of calcium uptake. 4. An approximate correlation exists between the calcium uptake and the sialic acid content of erythrocytes of various species and of human erythrocytes that have been partially depleted of sialic acid by treatment with neuraminidase. However, even after complete removal of sialic acid, human erythrocytes still bind about 140mug-atoms of calcium/litre of packed cells. 5. A Scatchard (1949) plot of calcium uptake at various Ca(2+) concentrations in the suspending media shows the presence of three different binding sites on the external surface of the human erythrocyte membrane. 6. Erythrocyte ;ghost' cells, the membranes of which appear to be permeable to Ca(2+) ions, can bind about 1000mug-atoms of calcium per ;ghost'-cell equivalent of 1 litre of packed erythrocytes. This indicates that there are also binding sites for calcium on the internal surface of the erythrocyte membrane.

Binding Sites↗
PubMed1971

A new reduced human-mouse somatic cell hybrid containing the human gene for adenine phosphoribosyltransferase.

A system that selects for the gene directing synthesis of the enzyme adenine phosphoribosyltransferase (APRT) uses the antibiotic alanosine to prevent endogenous synthesis of adenylic acid. With the aid of this system, a new series of human-mouse hybrids has been prepared between wild type human diploid fibroblasts and an enzyme-deficient mouse line. Survival of the hybrids depended upon the presence of the APRT, which was shown to have the isoelectric pH characteristic of the human enzyme and not that of the mouse. Reduced hybrids containing the enzyme lacked all human biarmed chromosomes, so that unless a rearrangement had occurred, the aprt gene must be located on an acrocentric chromosome. The hybrid cells became APRT(-) with a frequency of 2 x 10(-3), probably by loss of the human aprt chromosome. The APRT(-) progeny could be obtained selectively by growth in medium containing fluoroadenine.

Adenine↗
PubMed1968

The calcium content of human erythrocytes.

1. The calcium content of human erythrocytes, after removal of the buffy coat and washing free from plasma with isotonic sodium chloride, has been determined by atomic absorption spectrophotometry. The mean value found for normal subjects was 0.634 mug/ml. of packed erythrocytes (0.0158 mug-atom/ml.). The corresponding values for magnesium and zinc were 79.7 and 20.1 mug/ml., respectively.2. The calcium is considered to be mostly and perhaps exclusively located in the erythrocyte membrane, since, after osmotic haemolysis, the same amount was found in the ghost cells as was present in the erythrocytes from which they were prepared. By contrast, magnesium and zinc, which are essentially intracellular, were lost to the extent of about 96 and 92%, respectively.3. About 90% of the calcium was removed from erythrocytes by washing with isotonic sodium chloride containing 5 mM ethylenediaminetetraacetate (EDTA), or other complexing agents of high stability constant for calcium. A small fraction of the magnesium but none of the zinc was removed by this treatment.4. Other complexing agents of lower stability constant removed somewhat less calcium from the erythrocytes. Citrate was totally ineffective.5. The buffy coat had a high calcium content, but this could not be removed by washing with EDTA.6. Calcium was also determined in trichloroacetic acid extracts of ghost cells after ashing and treatment with bis-(o-hydroxyphenylimino)-ethane and measuring the red complex spectrophotometrically. The values obtained confirmed the atomic absorption measurements.

Calcium↗
PubMed1967

The action of cabbage-leaf phospholipase D upon lysolecithin.

1. The action of the water-soluble phospholipase D from Savoy cabbage leaves upon an aqueous solution of lysolecithin has been studied. 2. Optimum conditions required the presence of Ca(2+) ions and pH5.8. 3. Equivalence was found between the amounts of lysolecithin hydrolysed and free choline released. The reaction was not accompanied by deacylation. 4. As the enzymic degradation proceeded, an opalescence developed, owing to the insolubility of the reaction product in the presence of Ca(2+) ions. 5. Evidence has been obtained indicating the heterogeneity of this reaction product.

Calcium↗
PubMed1967

The chemical nature of the products obtained by the action of cabbage-leaf phospholipase D on lysolecithin: the structure of lysolecithin.

1. Lysolecithin, prepared by the action of snake-venom phospholipase A on ovolecithin, when incubated with Savoy-cabbage phospholipase D, in the presence of Ca(2+) ions, gave two degradation products (designated A and B) in the form of their calcium salts. 2. These calcium salts were separated quantitatively by solvent fractionation and converted into the corresponding sodium salts. 3. Substance B proved to be a lysophosphatidic acid of conventional structure (1-monoacyl-l-3-glycerophosphoric acid). When the phosphate group was removed by means of prostatic acid phosphomonoesterase, a 1-monoglyceride was formed quantitatively. Alkaline hydrolysis gave the theoretical yield of l-3-glycerophosphate. 4. Substance A, on the other hand, had all the properties expected for a cyclic phosphate of a 1-monoglyceride. It was unaffected by phosphomonoesterase. On alkaline hydrolysis, the acyl group was removed and ring opening of the presumed cyclic phosphate group gave an approximately equimolar mixture of 2- and l-3-glycerophosphates. 5. The structures of substances A and B confirm lysolecithin as 1-monoacyl-l-3-glycerylphosphorylcholine.

Acid Phosphatase↗
PubMed1966

Chromatographic behaviour of rat-liver monophosphoinositide.

1. Chromatography of rat-liver lipids on a column of silicic acid or a mixture of silicic acid and Hyflo Super-Cel, with chloroform-methanol mixtures, gave monophosphoinositide-containing fractions which were invariably contaminated by the presence of nitrogen-containing phospholipids. The behaviour of the inositide was extremely sensitive to column loading and the results with different batches of silicic acid were not reproducible. 2. However, when chromatography on an alumina column was used, the solvent system chloroform-methanol-water (23:23:4, by vol.) completely eluted the neutral lipids, choline-containing phospholipids and phosphatidylethanolamine. An increase of the water content of the solvent to 14% (by vol.) then led to the elution of the monophosphoinositide component, now free from nitrogen-containing phospholipids, but still contaminated by the presence of a phospholipid, which from its properties was taken to be polyglycerophosphatide. 3. Most of the polyglycerophosphatide could be removed from a rat-liver lipid extract by silicic acid chromatography with chloroform-methanol (19:1, v/v). The other phospholipids were then eluted and applied to an alumina column, whereby a monophosphoinositide fraction of much greater purity was obtained. 4. Further purification of the monophosphoinositide was achieved by chromatography on a mixture of silicic acid and cellulose powder. The final product was virtually pure by thin-layer chromatography and gave the expected analysis for monophosphoinositide.

Animals↗