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Biomedical subjects

U Henning

Publications and source records attributed to U Henning.

At least 127 records · Page 7Linked to original sources
PubMed1973

Cell envelope and shape of Escherichia coli K12.

Rod-shaped "ghosts" that are free of murein have been isolated from E. coli. The shape of these "ghosts" is maintained by a unit membrane soluble in sodium dodecyl sulfate. Ghosts consist of about 20-30% phospholipid (almost exclusively phosphatidylethanolamine) and 50-60% protein; a large fraction of the remaining material is lipopolysaccharide. Sodium dodecyl sulfate-gel electrophoresis reveals 4-5 different bands corresponding to molecular weights between 10,000 and 40,000. Treatment of ghosts with Pronase reduces this number to 3, and the rod shape still is not lost. Results of treatment of ghosts with a crude extract from Dictyostelium discoideum have supplied tentative evidence that at least one of these proteins is involved in the maintenance of rod shape. It does not appear too unlikely that these polypeptide chains are the final products of the genetic information specifying cellular shape.

Bacterial Proteins↗
PubMed1973

Model for the structure of the shape-maintaining layer of the Escherichia coli cell envelope.

The surface area per repeating murein unit (i.e. per molecule of diaminopimelate) has been determined for the cell envelopes of the Escherichia coli strains K-12 and W. This area was constantly found to be 1.3 nm(2). Using this value and other previously determined properties of E. coli murein, a three-dimensional model of murein is proposed. The model specifies a monomolecular layer in which disaccharide units are each 1.03 nm long, and the polysaccharide chains, all parallel, are 1.25 nm apart. The cross-linking peptide side-chains have the same atomic coordinates and are arranged above or below the polysaccharide chains.

Amino Acids↗
PubMed1972

Limiting availability of binding sites for dehydrogenases on the cell membrane of Escherichia coli.

Experiments are reported that demonstrate that in E. coli the pyridine nucleotide-independent D- and L-lactate dehydrogenases and the aerobic L-alpha-glycerophosphate dehydrogenase are membrane bound. These enzymes differed from succinate dehydrogenase in that they could be solubilized by treatment with nonionic detergent while succinate dehydrogenase could not. The binding of these enzymes to membrane was measured in mutants constitutive for the synthesis of various dehydrogenases: in cells in which the amount of dehydrogenases synthesized was greater than in others, the enzymes described above (except succinate dehydrogenase) were found in part in the soluble fraction of the cell extracts. Experiments of oxygen uptake indicate that when a fraction of the enzymes became soluble, this soluble fraction is no longer functional in respiration. These results indicate that it is possible to prevent membrane attachment of certain dehydrogenases by the excess production of other dehydrogenases; it may be that dehydrogenases compete for identical binding sites.

Binding Sites↗
PubMed1972

Molecular structure of the pyruvate dehydrogenase complex from Escherichia coli K-12.

The pyruvate dehydrogenase core complex from E. coli K-12, defined as the multienzyme complex that can be obtained with a unique polypeptide chain composition, has a molecular weight of 3.75 x 10(6). All results obtained agree with the following numerology. The core complex consists of 48 polypeptide chains. There are 16 chains (molecular weight = 100,000) of the pyruvate dehydrogenase component, 16 chains (molecular weight = 80,000) of the dihydrolipoamide dehydrogenase component, and 16 chains (molecular weight = 56,000) of the dihydrolipoamide dehydrogenase component. Usually, but not always, pyruvate dehydrogenase complex is produced in vivo containing at least 2-3 mol more of dimers of the pyruvate dehydrogenase component than the stoichiometric ratio with respect to the core complex. This "excess" component is bound differently than are the eight dimers in the core complex.

Acrylamides↗
PubMed1970

Malate dehydrogenase mutants in Escherichia coli K-12.

Mutants devoid of malate dehydrogenase activity have been isolated in Escherichia coli K-12. They do not possess detectable malate dehydrogenase when grown aerobically or anaerobically on glucose as sole carbon source. All mutants revert spontaneously; a few partial revertants have been found with a malate dehydrogenase exhibiting altered electrophoretic mobility. Therefore, only one such enzyme appears to exist in the strains examined. No evidence could be obtained for the presence of a malate dehydrogenase not linked to nicotinamide adenine dinucleotide. Mutants deficient in both malate dehydrogenase and phosphoenol pyruvate carboxylase activities will grow anaerobically on minimal glucose plus succinate medium; also, malate dehydrogenase mutants do not require succinate for anaerobic growth on glucose. The anaerobic pathway oxaloacetate to succinate or succinate to aspartate appears to be accomplished by aspartase. Malate dehydrogenase is coded for by a locus somewhere relatively near the histidine operon, i.e., a different chromosomal location than that known for other citric acid cycle enzymes.

Acyltransferases↗
PubMed1969

Effects of oleate starvation in a fatty acid auxotroph of Escherichia coli K-12.

The effects of oleate starvation on an oleate auxotroph of Escherichia coli K-12 were investigated. Following removal of oleate from the mutant growing in a minimal glycerol-peptone medium, the cells stopped making deoxyribonucleic acid, ribonucleic acid, protein, and phospholipids; they began to die exponentially and finally lysed. During oleate starvation in minimal medium minus peptone, inhibition of macromolecular syntheses and death occurred; however, lysis did not follow. When growth ceased, no further dying was observed. It is shown that none of the early effects (inhibition of macromolecular syntheses and death) can be due to leakiness of the cells, induction of a prophage or a colicin, or lack of energy sources. The cause of inhibition of macromolecular syntheses remained unknown. Since the rate of death was the same as the generation time under different conditions, it appears that death is due to the defective synthesis of some cellular structure (quite possibly, cytoplasmic membrane) during phospholipid deficiency. Lysis was found to require protein synthesis; electron microscopy revealed a peculiar type of "lysis from within"; i.e., the shape of the cells did not change but fragmentation of the inner layer of the cell envelope occurred. The murein was found to be unaltered. Most likely, lysis was a consequence of the cell's attempt to synthesize cytoplasmic membrane with altered phospholipid composition or during phospholipid deficiency. Several membrane functions (respiration, adenosine triphosphate formation, permeability) existing before oleate removal were not lost during starvation. Therefore, general damage to the membrane did not occur, and it could be that most, if not all, described effects were due to defective de novo membrane synthesis.

Adenosine Triphosphate↗