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Biomedical subjects

M Brenner

Publications and source records attributed to M Brenner.

At least 235 records · Page 13Linked to original sources
PubMed1978

Measurements of metabolites during cAMP oscillations of Dictyostelium discoideum.

During aggregation the cellular slime mold Dictyostelium discoideum synthesizes and releases pulses of cAMP about every five minutes. Current models proposed to explain this phenomenon postulate that oscillating levels of some key intracellular metabolite control the oscillatory synthesis of cAMP. We have assayed the levels of likely candidates for this metabolite during a cAMP oscillation, but have found them to remain constant. Compounds measured include ATP, GTP, glucose-1-phosphate, glucose-6-phosphate, isocitrate, alpha-ketoglutarate, amino acids, and other aminated metabolites. On the basis of this negative data, as well as results described elsewhere (Geller and Brenner, '78), we question whether the proposed models are correct, and discuss several alternatives.

Adenosine Triphosphate↗
PubMed1977

Cyclic AMP gradient in migrating pseudoplasmodia of the cellular slime mold Dictyostelium discoideum.

Several lines of experimental evidence suggest that an anterior-posterior gradient of cyclic AMP exists in migrating pseudoplasmodia of the cellular slime mold Dictyostelium discoideum, and that this gradient may be responsible for control of the proportions of stalk and spore cells that form during culmination. In experiments reported here, the amounts of cyclic AMP present in the anterior and posterior portions of pseudoplasmodia were measured using a protein binding assay, and the levels obtained normalized to protein and DNA. For a variety of pseudoplasmodia migration conditions examined, the anterior portion was found to contain cyclic AMP concentrations 40 to 70% higher than the posterior portions.

Cyclic AMP↗
PubMed1977

[Morphometry of breast tissue (author's transl)].

In conventional tissue slides it is possible to describe quantitatively the dysplasia of the breast with the aid of the Quantimet 720 and the image editor equipment. From several slides of each breast the areas of epithelium, lumina and connective tissue were measured out of 5 to 20 lobuli. The data were transformed into a descriptive index according to the formula: (epithelium--lumen): connective tissue. In normal mammae the indices are clustered and lower than 100. In the cases of increasing dysplasia the indices are scattered and elevated. In glands with carcinoma the normal values disappear, but the scattering and rising of indices increase. With these findings it seems possible to identify dysplasia in a precancerous state by morphometrical analysis.

Breast Diseases↗
PubMed1976

Membrane hybridization by centrifugation analysed by lipid phase transitions and reconstitution of NADH-oxidase-activity.

A procedure is described to hybridize cytoplasmic membranes of Escherichia coli. The method involves high-speed contrifugation of two different vesicle preparations at 37 degrees C in the presence of cations such as spermine or Mg2+. The occurrence of hybridization is shown by the following experiments. Firstly, formation of a mixed lipis phase starting from two membranes having a different hydrocarbon chain composition in their phospholipids. Secondly, formation of a hybrid membrane having an intermediate lipid to protein ratio from two membrane fractions having different lipid to protein ratios. Thirdly, reconstitution of NADH oxidase activity by hybridization of two membrane fractions, one lacking active cytochromes and the other being deficient in quinones. It is proposed that hybridization occurs by fusion of vesicles during the tight association of collapsed vesicles under high centrifugal forces. This interpretation is supported by electron microscopy of the membrane pellets after centrifugation. However, lipid transfer as the mechanism of hybridization cannot be excluded and attempts to reconstitute active galactoside transport by complementation of beta-galactoside transport-deficient membranes and cytochrome-deficient membranes have been unsuccessful.

Calcium↗
PubMed1975

Lipid phase transitions in cytoplasmic and outer membranes of Escherichia coli.

The cytoplasmic and outer membranes containing either trans-delta-9-octadecenoate, trans-delta-9-hexadecenoate or cis-delta-9-octadecenoate as predominant unsaturated fatty acid residues in the phospholipids were prepared from a fatty acid auxotroph, Escherichia coli strain K1062. Order-disorder transitions of the phospholipids were revealed in both fractions of the cell envelope by fluorescent probing or wide angle X-ray diffraction. The mid-transition temperatures, Tt, and the range of the transition, delta-T, are similar in the outer and cytoplasmic membrane. Relative to the corresponding extracted lipids, 60-80% of the hydrocarbon chains take part in the transition in the cytoplasmic membrane whereas in the outer membrane only 25-40% of the chains become ordered. The results suggest that in the outer membrane part of the lipids form fluid domains in the form of mono- and/or bilayers.

Cell Membrane↗
PubMed1973

Mutations affecting N-acetylglucosaminidase in Dictyostelium discoideum.

A procedure for screening several thousand clones for alterations in a specific gene product was apapplied to mutagenized cultures of Dictyostelium discoideum. Six strains were recovered which had less N-acetylglucosaminidase (EC 3.2.1.30) than the wild type. In addition, we isolated four strains in which the enzyme was temperature-sensitive. The enzyme from one of these strains had an altered substrate affinity.N-Acetylglucosaminidase is present at a low level in cells grown on bacteria and increases up to 10-fold during the aggregation stage of development. The enzyme appears to be essential to maintain migrating pseudoplasmodia of normal size, as shown by the fact that all of the mutant strains which accumulate very little N-acetyl-glucosaminidase formed only small migrating pseudoplasmodia containing less than 10% the number of cells found in the wild-type pseudoplasmodia. The small pseudoplasmodia migrated at less than a third the rate of wild-type pseudoplasmodia and ultimately formed diminutive fruiting bodies. N-Acetylglucosaminidase thus appears to be a developmental enzyme that functions during the migration stage.

Acetamides↗