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Biomedical subjects

H R Mahler

Publications and source records attributed to H R Mahler.

At least 73 records · Page 4Linked to original sources
PubMed1975

Subcellular and regional distribution of 125I-labeled alpha-bungarotoxin binding in rat brain and its relationship to acetylcholinesterase and choline acetyltransferase.

1. The subcellular distribution of binding sites for 125I-labeled alpha-bungarotoxin was studied in rat cerebral cortex. Primary fractions showing higher specific activity than homogenate were P2 (crude mitochondria and nerve endings) and P3-P2 was subfractionated on a Ficoll gradient with the P2B (nerve ending) subfraction exhibiting the greatest recovery (65%) and enrichment of toxin binding. Toxin binding showed a distribution similar to that of acetylcholinesterase, choline acetyltransferase, and sodium and potassium ion-activated ATPase. 2. P2B and P3 were subfractionated on five-step discontinuous sucrose gradients. The highest specific activity of toxin binding and acetylcholinesterase was associated with fractions of relatively low buoyant density, while choline acetyltransferase activity was associated with fractions of higher density. 3. Toxin binding, acetylcholinesterase, and choline acetyltransferase activities were relatively high in olfactory lobes, cerebral cortex, thalamic region, caudate nucleus, and brain stem; intermediate in hippocampus; low in cerebellum. 4. The relationship of toxin binding to the putative acetylcholine receptor in brain is discussed.

Acetylcholinesterase↗
PubMed1975

Synthesis of membrane protein in slices of rat cerebral cortex.

Protein synthesis was studied in slices from rat cerebral cortex and localized in various purified subcellular membrane fractions isolated after incubation with L-leucine. A synaptosomal fraction isolated from a several times washed crude mitochondrial pellet showed very little contamination by free membranes, and the synaptic membrane fraction isolated from it was estimated to c +ain about 50% of this component. Leucine incorporation into all fractions was highly sensitive (greater than 95%) to emetine except for the cell and synaptic mitochondrial subfractions. They were only 60 to 70% inhibited by emetine and showed 10 to 20% inhibition by chloramphenicol which probably was due to those proteins synthesized in situ by the mitochondria. The net rate of incorporation of labeled protein into the synaptosomal and synaptic membrane subfractions was low, and axonal flow was excluded as a significant source of this label. On the basis of autoradiography it was concluded that the majority of the protein label was contributed by free and membrane-enclosed ribosome-containing contaminants in these fractions. Unlabeled and labeled subcellular fractions were also analyzed by electrophoresis in the presence of sodium dodecyl sulfate. The staining profiles of the microsomal and synaptic membrane subfractions were nearly identical, whereas those of synaptic mitochondria and the soluble proteins of the cell bodies were unique. The labeling of all proteins was blocked by emetine, except for the synaptic mitochondria (cell mitochondria were not examined). These products of mitochondrial protein synthesis exhibited three labeling peaks, the major one with a molecular weight of approximately 38,000. In the absence of emetine, slices incorporated amino acids into soluble and microsomal proteins with high specific activity. The labeled proteins of the soluble fraction were more highly concentrated in the range of molecular weights smaller than 50,000 than were those in the microsomal fraction, and it was concluded that a considerable portion of the protein-synthesizing machinery of the brain is geared to form soluble proteins. The gel patterns of labeled microsomal and synaptic membranes were consistent with contamination by the former contributing most of the protein label in the latter.

Animals↗
PubMed1975

Derepression in Saccharomyces cerevisiae can be dissociated from cellular proliferation and deoxyribonucleic acid synthesis.

A method has been developed that permits precise control of release from catabolite repression in Saccharomyces cerevisiae. It consists of transferring cells growing exponentially on 5% glucose to derepression medium at high cell density. Derepression then proceeds with reproducible kinetics and is complete within 6 to 7.5 h for various intra- and extramitochondrial markers, in the absence of any substantial increase in cellular dry weight or protein. Nuclear (and mitochondrial) deoxyribonucleic acid synthesis can be interrupted in certain thermosensitive (cdc) mutants at the nonpermissive temperature; a shift to this temperature before the onset of derepression has no effect on its outcome.

Bacterial Proteins↗
PubMed1974

Coupling between mitochondrial mutation and energy transduction.

Upon incubation with ethidium bromide (Etd Br) isolated mitochondria of Saccharomyces cerevisiae have been shown to be capable of performing five novel reactions: (a) a single scission of their DNA (mtDNA) coincident with (b) the incorporation of Etd Br into the product (mtDNA --> 2 mtDNA'-Etd Br); (c) an energy- (and probably ATP-) requiring degradation of mtDNA'-Etd Br to acid-labile products. These reactions acting in series generate (d) a DNase dependent on both Etd Br and an energy supply with mtDNA'-Etd Br as an obligatory intermediate. Coincident with (d) there occurs (e) an activation of adenosinetriphosphatase. Experiments with specific inhibitors suggest that the enzyme responsible is the mitochondrial adenosinetriphosphatase complex itself, and that it and the ability to carry out reactions (a) through (e) are tightly coupled to the energy-transducing functions of the particle.

Adenosine Triphosphatases↗
PubMed1974

Nuclear gene dosage effects on mitochondrial mass and DNA.

In order to assess the effect of nuclear gene dosage on the regulation of mitochondria we have studied serial sections of a set of isogenic haploid and diploid cells of Saccharomyces cerevisiae, growing exponentially in the absence of catabolite repression, and determined the amount of mitochondrial DNA per cell. Mitochondria accounted for 14% of the cytoplasmic and 12% of the total cellular volume in all cells examined regardless of their ploidy or their apparent stage in the cell cycle. The mean number of mitochondria per cell was 22 in the diploid and 10 in the haploids. The volume distribution appeared unimodal and identical in haploids and diploids. The mitochondrial DNA accounted for 12.6 +/- 1.2% and 13.5 +/- 1.3% of the total cellular DNA in the diploid and haploid populations, respectively. These values correspond to 3.6 x 10(-15) g, 2.2 x 10(9) daltons, or 44 genomes (50 x 10(6) daltons each) per haploid and twice that per diploid cell. On this basis, the average mitochondrion in these cells contains four mitochondrial genomes in both the haploid and the diploid.

Alleles↗