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Biomedical subjects

W Epstein

Publications and source records attributed to W Epstein.

At least 109 records · Page 6Linked to original sources
PubMed1975

Allocation of attention and the locus of adaptation to displaced vision.

Experimental subjects were exposed to prism-induced visual displacement of a target whose location was correctly given by proprioceptive-kinesthetic information. Control subjects were exposed alternately to visual displacement or proprioceptive-kinesthetic location information. During the adaptation period, experimental subjects in the visual attention condition performed a localization task that directed them to attend selectively to the visual modality; experimental subjects in the proprioceptive attention condition attended selectively to the proprioceptive modaltiy; control subjects performed the task on the basis of the available modality. Measures of adaptation and aftereffect were secured separately in each of the two modalities. These confirmed the predictions that the shifts in the experimental conditions would be confirmed to localization tests dependent on the unattended modality and that control subjects would not exhibit adaptation. We proposed that allocation of attention determines situational dominance and that dominance determines the locus of adaptation. The findings were compared to those reported by Canon (1970) and were applied to a reassessment of the "visual capture" phenomenon.

Adaptation, Physiological↗
PubMed1975

Recalibration by pairing: a process of perceptual learning.

When two cues which normally agree in determining perceived depth are experimentally paired so that they designate discrepant values for the depth dimension, an opportunity is created for the recalibration or re-evaluation of the cues. Experiments which show recalibration of the oculomotor cues and recalibration of binocular disparity as a result of pairing these cues with other discrepant cues are reviewed. The locus of change is related to the relative dominance of different cues and the contribution of allocation of attention in determining dominance is discussed. Implications of recalibration by pairing for understanding ontogenetic development are considered. It is suggested that some cues may acquire their effectiveness as a consequence of pairing during development.

Cues↗
PubMed1975

Adenosine 3':5'-cyclic monophosphate as mediator of catabolite repression in Escherichia coli.

Measurements of intracellular adenosine 3':5'-cyclic monophosphate (cAMP) concentrations in E. coli under a variety of conditions show that levels of this nucleotide are well correlated with the rate of synthesis of beta-galactosidase (beta-D-galactoside galactohydrolase, EC 3.2.1.23) in both catabolite repression and transient repression. These results, combined with extensive genetic and in vitro studies from a number of laboratories on the role of cAMP in E. coli, provide strong support for the concept that intracellular cAMP levels mediate the effects of catabolite and transient repression on rates on enzyme synthesis. Under all conditions studied, excretion can be described by a single rate constant, 2.1 min-1 at 37 degrees, indicating that intracellular levels cannot be regulated by alterations in the rate of cAMP excretion. Our data are fully consistent with the idea that carbon sources control intracellular cAMP levels by effects on its synthesis.

Cyclic AMP↗
PubMed1975

Updating the maximization test for identifying contact allergens.

The maximization test for detecting contact allergens has proved to possess both sensitivity and specificity. However, modifications have become necessary because of excessive irritancy reactions to sodium lauryl sulfate. Fewer exposures are now recommended during induction and lower concentrations for challenge patch testing. Pre-testing of each subject in the panel is now standard procedure. The problem of interpreting challenge patch tests is discussed in detail.

Allergens↗
PubMed1975

Phosphorylation of D-glucose in Escherichia coli mutants defective in glucosephosphotransferase, mannosephosphotransferase, and glucokinase.

Genetic studies show that Escherichia coli has three enzymes capable of phosphorylating glucose: soluble adenosine 5'-triphosphate-dependent glucokinase, which plays only a minor role in glucose metabolism; an enzyme II, called glucosephosphotransferase, with high specificity for the D-glucose configuration; and another enzyme II, called mannosephosphotransferase, with broader specificity. The former enzyme II is active on glucose and methyl-alpha-glucopyranoside, whereas the latter is active on D-glucose, D-mannose, 2-deoxy-D-glucose, D-glucosamine, and D-mannosamine. Mutations leading to loss of glucosephosphotransferase activity and designated by the symbol gpt are between the purB and pyrC markers in a locus previously called cat. The locus of mutations to loss of mannosephosphotransferase, mpt, is between the eda and fadD genes. Mutations to loss of glucokinase, glk, are between the ptsI and dsd genes.

Chromosome Mapping↗
PubMed1974

Phosphotransferase-system enzymes as chemoreceptors for certain sugars in Escherichia coli chemotaxis.

For D-glucose and analogs there are two distinct phosphotransferase enzymes II with different specificities. Transport and chemotaxis were studied in E. coli mutants having only one or the other of these two enzymes. It was found that the transport specificity of a given enzyme II correlates with taxis specificity, and mutational loss of an enzyme II abolishes taxis toward only those sugars which it alone transports. Although enzyme I and the phosphate-carrier protein are required for full D-glucose taxis, it could not be determined if phosphorylation and transport are also required.

Bacterial Proteins↗
PubMed1974

Accumulation of toxic concentrations of methylglyoxal by wild-type Escherichia coli K-12.

Wild-type strains of Escherichia coli K-12 accumulate toxic concentrations of methylglyoxal when grown in medium containing adenosine 3',5'-monophosphate and either d-xylose, l-arabinose, or d-glucose-6-phosphate, independent of the presence of other carbon sources. Mutations at a locus called cxm specifically block methylglyoxal formation from xylose in the presence of adenosine 3',5'-monophosphate. Accumulation in medium containing xylose, studied in some detail, is dependent on the ability to utilize xylose and is associated with an increased rate of xylose utilization without changes in levels of xylose isomerase. These results suggest that adenosine 3',5'-monophosphate results in induction of excessively high levels of an early rate-limiting step in xylose metabolism. This step may be the transport of xylose into the cell. The resulting excessive rates of xylose catabolism could stimulate methylglyoxal formation by overburdening late steps in glycolysis.

Adenosine Monophosphate↗
PubMed1973

Role of cyclic adenosine 3',5'-monophosphate in the in vivo expression of the galactose operon of Escherichia coli.

Studies of levels of galactokinase in Escherichia coli with mutations affecting synthesis of, or response to, cyclic adenosine 3',5'-monophosphate show that this nucleotide does not play a major role in expression of the galactose operon, causing at most a twofold stimulation. The discrepancy between our in vivo results and the marked stimulation by cyclic adenosine 3',5'-monophosphate in in vitro systems indicates that current cell-free systems lack a factor which allows efficient expression of the galactose operon even in the absence of cyclic adenosine 3',5'-monophosphate or of the binding protein for this nucleotide.

Carbon Isotopes↗
PubMed1971

Valinomycin-induced uptake of potassium in membrane vesicles from Escherichia coli.

Osmotically shocked Escherichia coli and membrane vesicle ghosts from E. coli cells have lost the ability to accumulate potassium by active transport. The addition of valinomycin to the membrane ghosts restores the capacity to accumulate radioactive (42)K and (86)Rb by a temperature- and energy-dependent process. Membrane vesicles prepared from mutants of E. coli altered in potassium transport show defects in the valinomycin-stimulated accumulation of (42)K that are related to the defects in the intact cells.

Anti-Bacterial Agents↗
PubMed1971

Potassium transport loci in Escherichia coli K-12.

Mutants of Escherichia coli K-12 requiring considerably elevated concentrations of potassium for growth are readily obtained as double mutants combining a kdp mutation with a mutation in one or more of five other loci. These loci are referred to as trk, for transport of K, because these mutations result in alterations in K transport. The kdp mutation is essential in the isolation and identification of this type of mutant; in a Kdp(+) strain, the presence of a trk mutation does not prevent growth of the strain in media containing very low concentrations of K. The trk loci are widely scattered over the E. coli chromosome; none of them is very near any other trk locus or near the kdp genes.

Adenine↗