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At least 469 records · Page 26Linked to original sources
PubMed1981

Regulation of methyl beta-galactoside permease activity in pts and crr mutants of Salmonella typhimurium.

We have studied the regulation of the synthesis and activity of a major galactose transport system, that of methyl beta-galactoside (MglP), in mutants of Salmonella typhimurium. Two classes of mutation that result in a (partially) defective phosphoenolpyruvate: sugar phosphotransferase system (PTS) interfere with MglP synthesis. pts mutations, which eliminate the general proteins of the PTS Enzyme I and/or HPr and crr mutations, which result in a defective glucose-specific factor IIIGlc of the PTS, lead to a low MglP activity, as measured by methyl beta-galactoside transport. In both ptsH,I, and crr mutants the amount of galactose binding protein, one of the components of MglP, is only 5%-20% of that in wild-type cells, as measured with a specific antibody. We conclude that synthesis of MGlP is inhibited in pts and crr mutants. Once the transport system is synthesized, its transport activity is not sensitive to PTS sugars (i.e., no inducer exclusion occurs). The defect in pts and crr mutants with respect to MGlP synthesis can be relieved in two ways: by externally added cyclic adenosine 3',5-monophosphate (cAMP) or by a mutation in the cAMP binding protein. The conclusion that MglP synthesis is dependent on cAMP is supported by the finding that its synthesis is also defective in mutants that lack adenylate cyclase. pts and crr mutations do not affect growth of S. typhimurium on galactose, however, since the synthesis and activity of the other major galactose transport system, the galactose permease (GalP), is not sensitive to these mutations. If the galactose permease is eliminated by mutation, growth of pts and crr mutants on low concentrations of galactose becomes very slow due to inhibited MglP synthesis. Residual growth observed at high galactose concentrations is the result of yet another transport system with low affinity for galactose.

Bacterial Proteins↗
PubMed1976

Glycolysis and glycogen metabolism after inhibition of hexose monophosphate pathway in C6-GLIAL cells.

1. 6-Aminonicotinamide (0.01 mg/ml) leads to a strong accumulation of 6-PG in C6 glial cells after 24h. 2. The accumulated 6-PG is dephosphorylated to gluconate which easily permeates the cell membrane. Extracellular gluconate is formed at a rate of 12% of the total glucose consumption. 3. 6-PG as competitive inhibitor of the PG1 caused a reduction of the glycolytic flux of about 40%. 4. The reduced glycolytic flux lowers the ATP concentration under anaerobic conditions to 75% of the controls. 5. The glycogen content after 6-AN is increased by 50%, probably by the activation of the glycogen synthetase due to the higher Glc 6-P concentration. 6. The fibroblast-like morphology of the C6 cell line has typically changed under 6-aminonicotinamide.

6-Aminonicotinamide↗
PubMed1975

The effects of increased glucose supply and thiopental anesthesia on energy metabolism of the isolated perfused rat brain.

The effects of glucose concentrations in the perfusion medium ranging from 5 to 15 mM and thiopental, on cerebral energy metabolism were studied using the isolated perfused rat brain. After a perfusion time of 30 min brain levels of the following substrates and metabolites were determined: P-creatine, ATP, ADP, AMP, glycogen, glucose, glucose-6P, fructose-6-P, pyruvate, lactate, alpha-ketoglutarate, glutamate, ammonia. In control experiments increasing the glucose concentration in the perfusion medium produced an increase of intracellular brain glucose concentration only, revealing a linear relationship between glucose content in brain and blood. Neither high-energy phosphates nor glycolytic intermediates were markedly affected by the changes in blood glucose. With an anesthetic dose of thiopental (0.15 mM) in the perfusion medium identical metabolic alterations occured in all experiments: P-creatine and glucose were significantly increased whereas ADP, AMP, lactate and pyruvate were diminished. Also with thiopental brain glucose was linearly related with the glucose concentration in the perfusion medium. The calculated regression line was apparently parallel with that from control experiments; that means thipental always caused an elevation of brain glucose by the same amount of 0.9 mumoles/g--irrespective of the initial cerebral glucose content. The results yield further evidence that glucose transport is not the rate-limiting step in glycolysis. The action of thiopetal on glycolytic pathway is discussed.

Adenine Nucleotides↗
PubMed1977

Glucose metabolism in C-1300 neuroblastoma cells after inhibition of hexose monophosphate pathway.

1. Application of 6-AN (0.01 mg/ml) leads to a strong accumulation of 6-PG in C-1300 neuroblastoma cells which, however, only amounts to one third of that found in C-6 glial cells. 2. In C-1300 neuroblastoma cells dephosphorylation of the accumulated 6-PG causes a rise of the intracellular gluconate to eight times the value found for 6-PG. It is four times higher than the gluconate content observed in C-6 glial cells. 3. Although 6-PG is a competitive inhibitor of PGI it causes no reduction of glycolytic flux and ATP content in stationary phase C-1300 neuroblastoma cells in contrast to the strong reduction of glycolytic flux and ATP content observed in C-glial cells. 4. The intracellular Glc-6-P and Fru-6-P content of C-1300 neuroblastoma cells increases by four to five times after treatment with 6-AN. Both this increase and the decrease of Fru-1,6-P2 content point to an inhibition of the phosphofructokinase. 5. In contrast to C-6 glial cells no morphological changes could be observed in C-1300 neuroblastoma cells up to 24 h after administration of 6-AN.

6-Aminonicotinamide↗
PubMed1987

Involvement of the macrophage mannose-6-phosphate receptor in the recognition of Leishmania mexicana amazonensis.

Significant differences were found in the ability of resident mouse peritoneal macrophages to ingest amastigote and promastigote forms of Leishmania mexicana amazonensis. Differences in the association index of the parasites to the macrophages were also found between infective and non-infective promastigotes. Evidence was obtained suggesting that the macrophage receptor, which recognizes mannose-6-phosphate-containing units found in lysosomal enzymes, is involved in the association with the macrophage of promastigotes, but not of amastigotes. Addition of mannose-6-phosphate, its structural analogue fructose-1-phosphate, Hansenula holstii phosphomannan or the mannose-6-phosphate-containing lysosomal enzyme alpha-D-mannosidase to the interaction medium, markedly inhibits the association of the parasites with macrophages.

Animals↗