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Biomedical subjects

I Friedberg

Publications and source records attributed to I Friedberg.

45 records · Page 3Linked to original sources
PubMed1972

Localization of phosphoglucose isomerase in Escherichia coli and its relation to the induction of the hexose phosphate transport system.

The localization of phosphoglucose isomerase (PGI) was studied in relation to the induction of hexose phosphate uptake in Escherichia coli. The uptake system is induced only by extracellular glucose-6-phosphate (G6P); there is no induction by intracellular G6P. Fructose-6-phosphate (F6P) is an indirect inducer, and isomerization of F6P to G6P must occur before induction. PGI has been considered to be an internal enzyme; therefore, uptake of F6P by noninduced cells and leakage of the G6P formed would be required for induction. In this study, it was concluded that part of the PGI activity is located in the cell surface because: (i) uninduced, intact cells are able to convert F6P to G6P, whereas the activity of G6P dehydrogenase is not detectable; (ii) when cells are subjected to osmotic shock, about 10% of the PGI activity is found in the shock fluid; and (iii) sorbitol-6-phosphate (S6P) inhibits both PGI activity of whole cells and the induction of hexose phosphate transport system by F6P. S6P was not taken by intact cells. The data indicate that the isomerization of F6P to G6P can take place on the cell surface, and this explains the indirect induction of hexose phosphate transport by F6P.

Biological Transport↗
PubMed1971

Biogenesis and Degradation of Starch: I. The Fate of the Amyloplast Membranes during Maturation and Storage of Potato Tubers.

Storage of mature or developing potato tubers (Solanum tuberosum "Up-to-Date" variety) at 4 C causes a reduction in the starch content and the elevation in the level of free sugars. This phenomenon is not observed when the tubers are stored at 25 C. Changes in the morphology of cells from developing or mature tubers after storage at 4 or 25 C have been followed by electron microscopy. During all stages of the tuber development the starch granules are surrounded by a membrane derived from the plastid envelope. Storage in the cold induces disintegration of this membrane. A membrane fraction isolated from starch granules of tubers stored at 4 C has a lower buoyant density, and the electrophoretic pattern of its proteins is different from that of a similar membrane fraction obtained from tubers stored at 25 C. It is suggested that the cold-induced changes in the starch and sugar content during storage of potato tubers might be correlated with damage to the membranes surrounding the starch granules and changes in their permeability to degradative enzymes and substrates.

Journal Article↗
PubMed1970

Interaction of Gram-Negative Bacteria with the Lysosomal Fraction of Polymorphonuclear Leukocytes II. Changes in the Cell Envelope of Escherichia coli.

Interaction of lysosomal fraction with Escherichia coli caused damage to the cell envelope of these intact cells and to the cytoplasmic membrane of E. coli spheroplasts. The damage to the cytoplasmic membrane was manifested in the release of 260-nm absorbing material and beta-galactosidase from the spheroplasts, and by increased permeability of cryptic cells to O-nitrophenyl-beta-d-galactopyranoside; damage to the cell wall was measured by release of alkaline phosphatase. Microscope observation showed morphological changes in the cell envelope.

Journal Article↗
PubMed1968

Structures containing polyphosphate in Micrococcus lysodeikticus.

Granular structures containing inorganic polyphosphate were found in Micrococcus lysodeikticus. These structures were isolated by fractionation of the bacterial extract obtained by lysing the organisms with lysozyme. The composition of the fraction which was enriched with these structures was found to be: protein, 24%; lipids, 30%; and polyphosphate, 27%. This fraction also contained small amounts of ribonucleic acids, carbohydrate, and polyvalent cations. The effect of different reagents and enzymes on the integrity of the granules was examined. It was noticed that they accumulate in the bacteria during the logarithmic phase of growth but disappear gradually during the stationary phase.

Amino Sugars↗
PubMedDate not supplied

Heat-induced alterations in cell membrane permeability and cell inactivation of transformed mouse fibroblasts.

Hyperthermia, has recently been extended in many permutations as a modality of anticancer treatment, but the mechanisms underlying heat-induced cell inactivation are poorly understood. In this study, the role of the cell permeability barrier in the process of heat cytotoxicity are examined. Changes in cell membrane permeability were determined by following the efflux of normally impermeant metabolites, e.g. nucleotides, in cultures of Swiss mouse 3T3 cells, and their transformed derivatives, 3T6 cells. The increase in cell membrane permeability as a function of temperature and exposure duration was found to be characterized by a sigmoid curve, with a threshold value, above which the permeability markedly increased. A correlation was found between cell membrane permeabilization and cell inactivation. Both heat-induced permeabilization and heat cytotoxicity were more pronounced in the transformed cells, as compared to their untransformed counterparts. The temperature-dependent permeabilization was more effective in the presence of the ionophore amphotericin B. The data suggest that heat-induced lesion in the cell membrane has a major role in hyperthermia cytotoxicity.

Amphotericin B↗