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Biomedical subjects

W Epstein

Publications and source records attributed to W Epstein.

At least 127 records · Page 7Linked to original sources
PubMed1970

Potassium-dependant mutants of Escherichia coli K-12.

Mutants of Escherichia coli K-12 that grow more slowly in media containing low concentrations of K have been isolated. All independent mutants of this type which have been studied carry a mutation in a small region of the bacterial chromosome between the supE and gal loci. The growth rate of the mutants is the same as that of the parental strains in medium containing more than 1 mm K, but is only 50% that of the parent when the K concentration is reduced to 0.1 mm. The mutants do not appear to have a primary alteration in K transport, and are therefore referred to as K-dependent. The abbreviation kdp is proposed for this class of mutant.

Chromosomes, Bacterial↗
PubMed1970

Isolation and mapping of phosphotransferase mutants in Escherichia coli.

Mutants of Escherichia coli K-12 defective in enzyme I or Hpr, the two common components of the phosphoenolpyruvate-dependent phosphotransferase system, were isolated by a simple, direct method. The ptsI locus, the structural gene for enzyme I, and the ptsH locus, the site of mutations leading to loss of Hpr activity, are adjacent genes and could be part of a single operon. These two genes lie between the purC and supN markers in the order: strA... guaB-purC-ptsI-ptsH-supN-dsdA... his.

Chromosome Mapping↗
PubMed1967

Cation transport in Escherichia coli. VII. Potassium requirement for phosphate uptake.

When Escherichia coli K-12 is grown in media containing limiting amounts of K, growth continues normally until all the extracellular K has been consumed. Thereafter the rates of growth, glucose consumption, and oxygen consumption decrease progressively, and the cell contents of K and P fall. These changes, referred to as K limitation, are all reversed by the addition of K. By specifically altering the ionic composition of the cells it was shown that these metabolic disturbances are not due to changes in the cell content of K or Na, but are directly related to the absence of K from the extracellular medium. The cell pool of inorganic P and the uptake of PO(4) from the medium are low in K-limited cells and are immediately stimulated by the addition of K, suggesting that the primary effect of K limitation is to inhibit PO(4) uptake. All the metabolic effects of K limitation can be attributed to inhibition of PO(4) uptake. The requirement of extracellular K for PO(4) uptake may be due to a coupling between the uptake of K and PO(4).

Escherichia coli↗
PubMed1966

Cation transport in Escherichia coli. VI. K exchange.

K influx and net K flux have been measured in suspensions of chloramphenicol-arrested Escherichia coli. The rate of K exchange in the steady state was independent of the K concentration of the medium over a 200-fold range. Under a number of experimental conditions the rate of exchange may be considerably increased or decreased without changing the cellular K content. These results show that under these conditions changes in K influx are associated with equal changes in K efflux, and suggest that the latter process is, at least in part, both carrier-mediated and tightly coupled to the influx process.

Biological Transport↗