The status of the minimum principle in the theoretical analysis of visual perception.
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Depth Perception↗
Biomedical subjects
W Epstein
Publications and source records attributed to W Epstein.
Potassium transport in Escherichia coli: genetic and biochemical characterization of the K+-transporting ATPase.
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Adenosine Triphosphatases↗
Sequence homology between two membrane transport ATPases, the Kdp-ATPase of Escherichia coli and the Ca2+-ATPase of sarcoplasmic reticulum.
We have determined the DNA sequences of the genes encoding the three structural proteins of the Kdp-ATPase, an ATP-driven potassium transport system of Escherichia coli. Regions of the predicted amino acid sequence of KdpB, the phosphorylated protein of the system, are homologous to regions of the Ca2+-ATPase of rabbit sarcoplasmic reticulum. The phosphorylated aspartate residue of the latter is within a region of homology.
Adenosine Triphosphatases↗
Transglutaminase activity in human and rabbit ear comedogenesis: a histochemical study.
Using monodansylcadaverine as a fluorescent, lysine-substrate analogue, alterations in the histochemical profile of transglutaminase activity during human and coal tar-induced rabbit ear comedogenesis were examined. When compared to the normal pilosebaceous follicles of both species, a marked increase in enzyme-specific fluorescence in the hyperplastic epidermal lining and in the epithelium of the sebaceous duct was observed in human and rabbit early lesions. In mature human open and closed comedones, an intact band of transglutaminase activity corresponding to the differentiating epidermal cell layers was seen to surround the lesion. In mature rabbit comedones this band of activity was most striking. In most lesions, transglutaminase activity was closely apposed to the plasma membrane of the differentiating keratinocytes, the site of cornified envelope formation. In normal human and rabbit interfollicular epidermis the cornified layer immediately above the fluorescent granular layer was histochemically inactive, while the surface stratum corneum showed an increase in activity. A similar phenomenon was observed in many comedones. This pattern of activity may relate to the process of desquamation. Finally, the changes in transglutaminase activity observed during comedogenesis suggest the possibility that inhibitors of transglutaminase could be useful in acne therapy.
Acne Vulgaris↗
Interaction between IIIGlc of the phosphoenolpyruvate:sugar phosphotransferase system and glycerol kinase of Salmonella typhimurium.
Purified IIIGlc of the phosphoenolpyruvate:sugar phosphotransferase system of Salmonella typhimurium inhibits glycerol kinase. Phosphorylation of IIIGlc via phosphoenolpyruvate, enzyme I, and HPr abolishes this inhibition. The glycerol facilitator is not inhibited by IIIGlc. It is proposed that regulation of glycerol metabolism by the phosphoenolpyruvate:sugar phosphotransferase system is at the level of glycerol kinase.
Bacterial Proteins↗
Tetracycline resistance element of pBR322 mediates potassium transport.
The tetracycline resistance element of plasmid pBR322 partially complements the potassium transport defect of Escherichia coli K-12 mutants having markedly impaired K+ transport. The plasmid increases K+ transport. The Tn10 element does not result in increased transport, demonstrating that the effect is not general for elements that increase resistance to tetracycline.
Drug Resistance, Microbial↗
Coactivation and comprehension: contribution of text variables to the illusion of knowing.
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Achievement↗
Purification and characterization of adenylate cyclase from Escherichia coli K12.
Adenylate cyclase of Escherichia coli K12 has been purified 17,000-fold to near homogeneity from a 5-fold overproducing strain. One major band of Mr = 92,000 and several minor bands are seen on sodium dodecyl sulfate-polyacrylamide electrophoresis of the purest fractions. Identification of the enzyme with the 92,000-Da protein is based on the correlation of this band with activity when highly purified enzyme is eluted from ADP-sepharose columns. The native enzyme has a molecular weight of 95,000 determined by gel filtration, showing that the enzyme is active as a monomer. The purest enzyme has a specific activity of 700 nmol min-1 mg-1, indicating a turnover number of about 100 min-1. Our data indicate that there are only about 15 molecules of the enzyme in wild type cells of E. coli. In crude extracts, over 80% of the activity is soluble after centrifugation at 100,000 x g, indicating the enzyme is soluble or, at most, loosely membrane bound. The enzyme is only moderately stable in crude extracts and becomes more unstable as purification proceeds. Activity is stabilized by ATP, or at -20 degrees C as an ammonium sulfate precipitate or in 50% glycerol. The enzyme has an absolute requirement for divalent cations. Maximum activity with Mg2+ is reached at 30 mM. Mn2+ is a good substitute; Co2+ activates well at low concentrations but becomes inhibitory at high concentrations; and Ca2+ is a potent inhibitor in the presence of Mg2+. The isoelectric point of the enzyme is 6.1, and its pH optimum is 8.5. The enzyme is inhibited by its substrate, with a Km of about 1 mM and a Ki of about 1.5 mM, and is noncompetitively inhibited by PPi, ADP, GTP, and a number of other compounds. The data suggest that dissociation of PPi from the first enzyme-product complex is the rate-limiting step in the reaction. Activation of the enzyme, inferred to occur in vivo, could be produced by a postulated regulatory effector which speeds release of PPi from the enzyme-product complex.
3',5'-Cyclic-AMP Phosphodiesterases↗
The relationship between texture gradient and perceived slant-in-depth: direct or mediated?
Judgments were obtained of the surface texture and rotation in depth of a briefly-exposed monocularly-viewed rectangular grid rotated in depth and a set of projective equivalents of the grid presented in the frontal parallel plane. The judgements were secured when the grids were presented alone and when they were followed by a masking textured surface after interstimulus intervals (ISIs) ranging from 0 to 120 ms. In the absence of the mask judged texture varied corresponding to the variations of optical texture both for the rotated rectangular grids and the frontalparallel projections. Judgements of orientation in the absence of the mask varied corresponding to the variations in objective orientation for the rectangular grid and corresponding to the projective equivalent rotations for the frontalparallel projections. Introduction of the mask at ISI = O led to disruption of discriminative gradient and orientation judgments. The degree of disruption decreased as ISI increased. These findings were interpreted as supporting a mediational hypothesis of the relationship between optical texture and perceived slant-in-depth. In contrast to the direct perception hypothesis advanced by Gibson, the mediational hypothesis assigns and important role to the perceptual representation to the optical gradient. When the formation of this representation is arrested by processing of the mask, the relationship between optical texture and perceived slant-in-depth is disrupted.
Cues↗
Percept-percept couplings.
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Depth Perception↗
Osmotic control of kdp operon expression in Escherichia coli.
Turgor pressure, the difference in osmotic pressure across the inner membrane, has been found to regulate expression of the kdp operon in Escherichia coli. The kdp operon codes for a high-affinity repressible transport system for the uptake of potassium. We have studied the regulation of Kdp expression in a strain in which the gene for beta-galactosidase, lacZ, was placed under control of the kdp promotor. Neither internal nor external K+ concentrations directly controlled Kdp expression. Only when the external K+ concentration was reduced to the point of limiting growth was the kdp operon expressed. An increase in external osmolarity at constant K+ concentration, a procedure that reduces turgor pressure, caused expression of the kdp operon. As the magnitude of the osmotic shift was increased, corresponding to greater decreases in turgor pressure, the amount of Kdp expression also increased. The kdp operon thus appears to be controlled by changes in a physical force, the turgor pressure.
Biological Transport, Active↗
Role of the membrane potential in bacterial resistance to aminoglycoside antibiotics.
The electrical potential difference (delta psi) across the membrane of Escherichia coli was measured by the distribution of lipid-soluble cations and correlated with resistance to dihydrostreptomycin, where resistance is presumed due to reduced uptake of the drug. A good correlation between the two measured parameters was found under all conditions tested, which included effects of several mutations, inhibitors, changes in pH, and osmolarity. The most dramatic changes were seen when pH was varied; in wild-type strains resistance increased more than 100-fold, and delta psi fell by 70 mV when pH was reduced from 8.5 to 5.5. These results were interpreted as support for a model in which the uptake of the polycationic aminoglycosides is electrogenic and therefore driven by delta psi. The factor common to mutations and conditions which increase resistance was a reduction in delta psi. A simple model was developed which relates the minimal inhibitory concentration to the rate of aminoglycoside uptake and the rate of growth.
2,4-Dinitrophenol↗
Escherichia coli mutants in which transcription is dependent on recA function.
A gene essential for viability in recA mutants of Escherichia coli K-12 was identified. This gene, rdg for recA-dependent growth, is near 16 min on the E. coli chromosome between phr and gltA and is 90% cotransduced with gltA. In a strain with an rdg deletion and the temperature-sensitive recA allele, recA200, growth stopped within 7 min after cells were shifted to the nonpermissive temperature (42 degrees C). The cells remained viable for many hours at 42 degrees C. The defect at the nonpermissive temperature is in ribonucleic acid synthesis, which was completely shut off within 20 min after the temperature shift. Protein synthesis was also shut off, but deoxyribonucleic acid synthesis continued for at least 2 h after the shift. The rdg mutation alone had no apparent effect on growth, deoxyribonucleic acid repair, or recombination.
Bacterial Proteins↗
Perception of relative velocity: a revision of the hypothesis of relational determination.
The conventional formulation of the hypothesis of relational determination asserts that the perceived relative velocities of two or more objects depend upon their relative rates of displacement with respect to stationary referents in the visual field. Experiment 1 showed that this formulation is too restrictive by demonstrating the transposition-of-velocity effect under conditions in which two light spots moved in the absence of static visible contours and traversed unequal path lengths. Experiment 2 showed that angular velocity per unit of relative angular extent, and not relative linear or perceived extent, of the respective motion paths influences perceived relative velocity in nonarticulated space. The retinal dimensions of static visible frameworks were shown in experiment 3 to influence perceived relative velocity in a direction consistent with the conventional formulation of the relational-determination hypothesis, but the weight of the evidence suggested a reformulation along the following lines: the perceived relative velocities of two objects are significantly affected by the proportions of the retinal projections of the respective movement fields traversed by the two objects in the same unit of time, even when the motion fields consist only of the objects' motion paths.
Discrimination Learning↗
A potent contact allergen of Phacelia (Hydrophyllaceae).
The major contact allergen of Phacelia crenulata (Hydrophyllaceae) has been identified as geranylhydroquinone. A maximization test of geranylhydroquinone showed this to be a potent sensitizer comparable in degree to poison oak/ivy urushiol. Comparative patch testing on humans with urushiol established that the phacelia allergen does not cross-react with poison oak or ivy.
Allergens↗
Work disability in rheumatoid arthritis: effects of disease, social, and work factors.
We explore here the relative contribution of selected disease, social, and work-related factors to disability status in a population of persons with rheumatoid arthritis. Our study differs from previous studies in that it is limited to one diagnostic entity, yet at the same time evaluates a broad range of social and work-related factors in disability. One hundred-eighty persons with rheumatoid arthritis sampled from 19 socially diverse practice settings were given a structured survey about their medical and work histories and social backgrounds. We found significant effects of stage and duration of illness on continued employment but no positive effect of selected therapies. Social and work factors combined had a far larger effect on work disability than all disease factors. Among work factors, control over the pace and activities of work and self-employment status had the greatest effect on continued employment, suggesting that time control issues are crucial to the maintenance of one's job after onset of this illness.
Absenteeism↗
Toward an epidemiology of work disability.
The indirect cost of illness due to lost wages exceeds the cost of medical services by a large margin. Social characteristics of persons with physical impairment are more important than the characteristics of their medical condition in predicting whether disability will lead to work loss. Public policy toward disability currently emphasizes the "human capital" with which persons with impairments confront the labor market; this study suggests a new emphasis on social characteristics of the workplace.
Arthritis, Rheumatoid↗
Thallous ion is accumulated by potassium transport systems in Escherichia coli.
The accumulation of 204T1+ by Escherichia coli occurs primarily via either of two K+ transport systems called Kdp and TrkA. T1+ influx is inhibited and T1+ efflux is stimulated by the addition of K+ to the assay medium. Mutants defective in both the Kdp and TrkA systems accumulate little T1+. Uptake of triphenylmethylphosphonium, a lipid-soluble cation whose distribution is widely used to estimate the membrane electrical potential in bacteria, occurs to about the same extent in mutants that accumulate little T1+ as in strains that accumulate T1+ to high levels. These findings indicate that T1+ may be useful as a probe of bacterial K+ transport systems but is not a reliable indicator of the membrane electrical potential in E. coli.
Biological Transport, Active↗