Biomedical subjects

J B Stock

Publications and source records attributed to J B Stock.

57 records · Page 4Linked to original sources

PubMed1980

Enzymes II of the phosphotransferase system do not catalyze sugar transport in the absence of phosphorylation.

In Salmonella typhimurium, glucose, mannose, and fructose are normally transported and phosphorylated by the phosphoenolpyruvate:sugar phosphotransferase system. We have investigated the transport of these sugars and their non-metabolizable analogs in mutant strains lacking the phospho-carrier proteins of the phosphoenolpyruvate:sugar phosphotransferase system, the enzymes I and HPr, to determine whether the sugar-specific, membrane-bound components of the phosphonenolpyruvate: sugar phosphotransferase system, the enzymes II, can catalyze the uptake of these sugars in the absence of phosphorylation. This process does not occur. We have also isolated mutant strains which lack enzyme I and HPr, but have regained the ability to grow on mannose or fructose. These mutants contained elevated levels of mannokinase (fructokinase). In addition, growth on mannose required constitutive synthesis of the galactose permease. When strains were constructed which lacked the galactose permease, they were unable to grow even on high concentrations of mannose, although elevated levels of mannokinase (fructokinase) were present. These results substantiate the conclusion that the enzymes II of the phosphoenolpyruvate:sugar phosphotransferase system are unable to carry out facilitated diffusion.

Biological Transport, Active↗

PubMed1978

A protein methylesterase involved in bacterial sensing.

A protein methylesterase has been identified in soluble extracts of Salmonella typhimurium and Escherichia coli. This enzyme catalyzes the hydrolysis of gamma-glutamyl methyl ester residues from membrane-bound 60,000-molecular weight proteins that are essential for chemotaxis. Analyses of methylesterase activity in a variety of chemotactically defective strains suggest that the methylesterase is a product of the cheX gene in Salmonella and the cheB gene in E. coli. In addition, the cheT gene product in S. typhimurium seems to play a role in expression of methylesterase activity. Mutant strains lacking the protein methylesterase tumble incessantly in the absence of attractant gradients. This behavior is the converse of that shown by mutant strains defective in methyltransferase activity, which swim smoothly in the absence of repellent gradients. This finding indicates that reversible methylation acts as a control mechanism and that both a methyltransferase and a protein methylesterase are instrumental in bacterial sensing.

Chemotaxis↗

PubMed1977

Periplasmic space in Salmonella typhimurium and Escherichia coli.

The volume of the periplasmic space in Escherichia coli and Salmonella typhimurium cells was measured. This space, in cells grown and collected under conditions routinely used in work with these bacteria, was shown to comprise from 20 to 40% of the total cell volume. Further studies were conducted to determine the osmotic relationships between the periplasm, the external milieu, and the cytoplasm. Results showed that there is a Donnan equilibrium between the periplasm and the extracellular fluid, and that the periplasm and cytoplasm are isoosmotic. In minimal salts medium, the osmotic strength of the cell interior was estimated to be approximately 300 mosM, with a net pressure of approximately 3.5 atm being applied to the cell wall. A corollary of these findings was that an electrical potential exists across the outer membrane. This potential was measured by determining the distributions of Na+ and Cl- between the periplasm and the cell exterior. The potential varied with the ionic strength of the medium; for cells in minimal salts medium it was approximately 30 mV, negative inside.

Acetylglucosamine↗