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J M Moehring

Publications and source records attributed to J M Moehring.

43 records · Page 3Linked to original sources
PubMed1968

The response of cultured mammalian cells to diphtheria toxin. II. The resistant cell: enhancement of toxin action by poly-L-ornithine.

We have investigated the response of the resistant mouse L cell to diphtheria toxin. Intact cells and cell-free systems were studied. It was determined that the cell-free system is as sensitive to toxin as those from sensitive reticulocyte, HeLa, and KB cells previously studied. Poly-L-ornithine, reported to stimulate macromolecular uptake, enhanced toxin activity under conditions which also stimulated acid phosphatase activity. Resistance, in the L cell, appears to be linked to the cell membrane and the process of macromolecular uptake, and not to any intrinsic property of either the polyribosomes or associated protein synthesizing factors. Because of the unique way in which diphtheria toxin inhibits protein synthesis, the ability of poly-L-ornthine to enhance this action provides convincing evidence that poly-L-ornithine stimulates a true absorption of macromolecules and not just increased surface adsorption.

Acid Phosphatase↗
PubMed1968

Response of cultured mammalian cells to diphtheria toxin. 3. Inhibition of protein synthesis studied at the subcellular level.

Diphtheria toxin inhibited protein synthesis in intact KB cells. The action of the toxin upon the cell did not result in disaggregation of polyribosomes, or in impairment of their ability to function in protein synthesis. A reduction in single ribosomes and a concomitant increase in polyribosomes did result from the action of toxin. Nascent peptides were not cleaved from polyribosomes by the action of toxin, but treatment of fully intoxicated cells with puromycin resulted in cleavage of these peptides, and caused accelerated polyribosome breakdown. Our data indicated that the toxin must enter the cell to exert its effect. The component or components sensitive to toxin were localized in the 100,000 x g supernatant fraction of cytoplasmic extracts. When extracts from intoxicated cells were treated with nicotinamide, a significant proportion of their capacity to synthesize protein was restored. The specificity of this reaction suggested that nicotinamide adenine dinucleotide is involved in the action of toxin in the intact cell, and that one component inactivated by toxin is soluble transferase II.

Amino Acids↗
PubMed1967

The response of cultured mammalian cells to diphtheria toxin. I. Amino acid transport, accumulation, and incorporation in normal and intoxicated sensitive cells.

The response to diphtheria toxin of two sensitive cell lines, KB and HeLa, was investigated. Inhibition of the incorporation of radioactively labeled amino acids into protein was the earliest detectable effect of diphtheria toxin. It was observed that, during the period of intoxication, the cell membrane was morphologically intact and retained its semi-permeable character, although it was rendered fragile and more easily disrupted by mechanical manipulations than the normal cell. The transport of amino acids continued even after intoxicated cells had ceased to synthesize protein, and the levels accumulated were equal to those of control cells. It was observed that cultural conditions, age, and handling of cells affected their response to toxin. In early log phase cells subjected to a minimum of handling before application of the toxin, the normally observed latent period preceding detectable effects was reduced to 15 min for KB cells and 30 min for HeLa cells, shorter times than previously reported. The data are consistent with the hypothesis that diphtheria toxin enters susceptible cells, possibly by pinocytosis, and there acts upon cytoplasmic sites of protein synthesis.

Amino Acids↗