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D M Gill

Publications and source records attributed to D M Gill.

At least 73 records · Page 4Linked to original sources
PubMed1976

Mechanism of activation adenylate cyclase in vitro by polymyxin-released, heat-labile enterotoxin of Escherichia coli.

Heat-labile enterotoxic material released from Escherichia coli by polymyxin B activates the adenylate cyclase of pigeon erythrocyte ghosts in a time- and concentration-dependent manner. The activation requires nicotinamide adenine dinucleotide, adenosine triphosphate, and another component of the erythrocyte supernatant. The active species has a molecular weight of about 23,000-24,000 daltons, is inhibited by antibodies to the toxin of Vibrio cholerae, and is not irreversibly denatured by sodium dodecyl sulfate. Thus in many respects the active species from E. coli behaves the same as peptide A1 of cholera toxin.

Adenosine Triphosphate↗
PubMed1976

Multiple roles of erythrocyte supernatant in the activation of adenylate cyclase by Vibrio cholerae toxin in vitro.

Peptide A1 of Vibrio cholerae toxin, nicotinamide adenine dinucleotide, adenosine triphosphate, and a soluble protein present in erythrocyte supernatant are required for the activation of pigeon erythrocyte ghost adenylate cyclase but are not required to maintain the activated state. The compounds are all required simultaneously, and when all are added to ghosts, adenylate cyclase activity increases at a linear rate without delay. Under optimal conditions significant activation of cyclase is given by less than one molecule of toxin per ghost. Intact cholera toxin may be inactive in vitro. There is a delay of about 1 min between the addition of intact toxin and the attainment of the final rate of increase of adenylate cyclase activity. During this period, glutathione reduces the disulfide bond between peptides A1 and A2. The delay is eliminated if the toxin is reduced before addition. More A1 is liberated if the toxin is also denatured with sodium dodecyl sulfate.

Adenosine Triphosphate↗
PubMed1975

The mechanism of action of cholera toxin in pigeon erythrocyte lysates.

The adenylate cyclase activity of intact pigeon erythrocytes begins to rise after about 20 min of exposure to cholera toxin. The maximum rate at which the cyclase activity increases appears to be limited by the number of toxin molecules which can reach an intracellular target. If the erythrocytes are made permeable to the toxin by a bacterial hemolysin, no such limit exists, and adenylate cyclase activity starts to rise immediately upon the addition of toxin, and continues to rise to a maximum at an initially constant rate which is dependent upon the concentration of toxin. On lysed erythrocytes, the addition of cholera antitoxin immediately prevents any further rise in adenylate cyclase activity, but does not reverse any activation already achieved. Erythrocyte lysates may also be activated by isolated peptide A1 of cholera toxin, although activation of adenylate cyclase of intact erythrocytes requires the complete toxin molecule. In the intact cells, toxin first attaches by its Component B to surface receptors of which there are about 30 per erythrocyte. Subsequently, peptide A1 but not Component B is inserted into the erythrocyte. It takes only about 1 min at 37 degrees for peptide A1 to be sufficiently deep within the cell membrane to be inaccessible to extracellular antitoxin, but its complete transit through the membrane appears to take longer. The surface receptors are used only once, for they remain blocked by Component B. The number of receptors available on the surface may be increased by soaking cells in ganglioside GM1. Cholera toxin also decreases the rate of apparently spontaneous loss of adenylate cyclase activity and increases the response to epinephrine. Theophylline inhibits the action of cholera toxin.

Adenylyl Cyclases↗
PubMed1975

Involvement of nicotinamide adenine dinucleotide in the action of cholera toxin in vitro.

NAD is a necessary cofactor for the activation of adenylate cyclase (ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1) by cholera toxin. Lysates of certain types of cell that hydrolyze their endogenous store of NAD after cell disruption respond poorly or not at all to cholera toxin. Lysates of pigeon erythrocytes, which lack enzymes that degrade NAD, provide a convenient and reproducible system for assaying the activity of cholera toxin in vitro and allow investigation of the mechanism of action of the toxin upon broken cells.

Adenylyl Cyclases↗
PubMed1974

Concentration of elongation factor 2 in rat skeletal muscle during protein depletion and re-feeding.

Rat skeletal-muscle elongation factor 2 was assayed by causing it to react with NAD(+) by using fragment A of diphtheria toxin as the catalyst. Dietary protein restriction decreased the concentration of elongation factor 2 in homogenates of whole muscle. These decreases paralleled a decline in muscle RNA so that the number of molecules of elongation factor 2 per ribosome appeared to be independent of the diet. We conclude that elongation factor 2 is probably not the factor limiting the rate of muscle protein synthesis and is not responsible for the fall in the protein-synthetic rate in vivo observed in the muscles of animals whose dietary protein intake is inadequate.

Animals↗
PubMed1973

Diphtheria.

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Animals↗
PubMed1970

Action of diphtheria toxin in the guinea pig.

The blood clearance and distribution in the tissues of (125)I after intravenous injection of small doses (1.5-5 MLD or 0.08-0.25 microg) of (125)I-labeled diphtheria toxin has been followed in guinea pigs and rabbits and compared with the fate of equivalent amounts of injected (125)I-labeled toxoid and bovine serum albumin. Toxoid disappeared most rapidly from the blood stream and label accumulated and was retained in liver, spleen, and especially in kidney. Both toxin and BSA behaved differently. Label was found widely distributed among all the organs except the nervous system and its rate of disappearance from the tissues paralleled its disappearance from the circulation. There was no evidence for any particular affinity of toxin for muscle tissue or for a "target" organ. Previous reports by others that toxin causes specific and selective impairment of protein synthesis in muscle tissue were not confirmed. On the contrary, both in guinea pigs and rabbits, a reduced rate of protein synthesis was observed in all tissues that had taken up the toxin label. In tissues removed from intoxicated animals of both species there was an associated reduction in aminoacyl transferase 2 content. It is concluded that the primary action of diphtheria toxin in the living animal is to effect the inactivation of aminoacyl transferase 2. The resulting inhibition in rate of protein synthesis leads to morphologic damage in all tissues reached by the toxin and ultimately to death of the animal.

Amino Acids↗
PubMed1969

Studies on the mode of action of diphtheria toxin. VII. Toxin-stimulated hydrolysis of nicotinamide adenine dinucleotide in mammalian cell extracts.

When diphtheria toxin and NAD are added to soluble fractions containing aminoacyl transfer enzymes isolated from rabbit reticulocytes or from HeLa cells, free nicotinamide is released and, simultaneously, an inactive ADP ribose derivative of transferase II is formed. The reaction is reversible, and in the presence of excess nicotinamide, toxin catalyzes the restoration of aminoacyl transfer activity in intoxicated preparations. In living cultures of HeLa cells, the internal NAD concentration is sufficiently high to account for the rapid conversion, catalyzed by a few toxin molecules located in the cell membrane, of the entire cell content of free transferase II to its inactive ADP ribose derivative. Completely inactive ammonium sulfate fractions containing soluble proteins isolated from cells that have been exposed for several hours to excess toxin, can be reactivated to full aminoacyl transfer activity by addition of nicotinamide together with diphtheria toxin. Transferase II appears to be a highly specific substrate for the toxin-stimulated splitting of NAD and thus far no other protein acceptor for the ADP ribose moiety has been found.

Amino Acids↗