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Biomedical subjects

E Whitney

Publications and source records attributed to E Whitney.

34 records · Page 2Linked to original sources
PubMed1972

Manganese-resistant mutants of Escherichia coli: physiological and genetic studies.

Manganese is growth inhibitory for Escherichia coli. The manganese concentration required for inhibition is dependent upon the magnesium concentration of the medium. Mutants have been isolated which are partially resistant to manganese inhibition in both liquid and solid media. From conjugation experiments, the genetic locus for manganese-resistance, mng, appears to be between 34 and 37 min on the E. coli genetic map. Experiments with radioactive (28)Mg lead to the tentative conclusion that the mng mutants are altered in the inhibition constant for manganese as a competitive inhibitor for the mangnesium accumulation system. Once high manganese enters the cells, it displaces internal magnesium and leads to a net cellular loss and hence growth inhibition. The mng mutants are somewhat less subject to manganese-induced magnesium loss under comparable conditions than are manganese-sensitive wild-type cells.

Biological Transport↗
PubMed1970

Colicin-tolerant mutants of Escherichia coli: resistance of membranes to colicin E1.

Colicin E1 blocks proline accumulation by membrane vesicles prepared from wild-type sensitive Escherichia coli. Two classes of mutant cells are unaffected by colicin. Vesicles from colicin-resistant strains are sensitive to colicin E1, whereas vesicles from colicin-tolerant strains are unaffected by colicin El. These results suggest that the colicin E1 receptor is on the cell membrane and that colicin-tolerant strains have altered membranes while colicin-resistant strains have altered cell walls.

Biological Transport↗
PubMed1970

Two viruses isolated from rodents (Clethrionomys gapperi and Microtus pennsvlvanicus) trapped in St. Lawrence County, New York.

Four strains of C. gapperi virus were isolated from 3 Clethrionomys gapperi and 47 strains of Microtus virus from 15 Microtus pennsylvanicus and 1 Mus musculus. One of the Microtus strains was isolated from a pool of 20 mites while the others were from rodent tissues. These agehts were insensitive to ether and sodium desoxycholate, withstood freezing at -70 C for 3 years and lyophilization without loss of titer, and were not killed when heated at 60 C for 1 hour. Their size as determined by filtration was less than 50 mg and greater than 20-35 mmicro. The strains within each group appear to be similar. The illness induced in suckling mice by the C. gapperi agents had a 5-day incubation period followed by prostration and death with a histologic picture of extensive encephalomalacia. The incubation period in mice for the Microtus agents was 9 to 11 days followed by convulsions and death. Histopathology showed meningeal infiltration and necrosis of the molecular layer. No antigenic similarity was detected between the C. gapperi and Microtus viruses by cross complement-fixation test.

Animals↗
PubMedDate not supplied

Computational simulations of mitral regurgitation quantification using the flow convergence method: comparison of hemispheric and hemielliptic formulae.

Mitral regurgitation results from the incomplete closure of the mitral valve, and the noninvasive diagnosis of this disease remains an important clinical goal. In this study, steady flow computer simulations were used to evaluate flow convergence method for flow rate estimation. The hemispheric and hemielliptic formulae were compared for accuracy in the presence of complicating factors such as ventricular confinement, orifice shape, and aortic outflow. Results showed that in the absence of aortic outflow and ventricular confinement, there was a plateau zone where the hemispheric formula approximated the true flow rate, independent of orifice shape. However, in the presence of complicating factors such as aortic outflow and ventricular confinement, there was no clear zone where the hemispheric formula could be applied. The hemielliptic formula, however, worked in all cases, regardless of chamber size or magnitude of aortic outflow. Therefore, application of the hemielliptic formula should be considered in future clinical studies.

Aorta, Thoracic↗
PubMedDate not supplied

Comparison of crystal structure and theory for 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine.

The crystal structure of the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b] pyridine (PhIP) has been determined by single-crystal X-ray crystallography. Crystals grown by evaporation of an aqueous solution form in the monoclinic space group P2(1)/n with two molecules of PhIP per asymmetric unit, along with six water molecules. The phenyl groups of these two PhIP molecules have torsion angles of different magnitude with respect to the plane of the imidazopyridine moiety. To maintain centrosymmetry, the crystal also contains an oppositely torsioned symmetry equivalent of each. The amino groups of both PhIP molecules take part in an extensive hydrogen bond network with the water of crystallization, forming long channels through the crystals parallel to the crystallographic b axis. The diffraction results are compared to theoretical calculations of the optimized geometry for a single PhIP molecule in vacuo as well as with water hydrogen-bonded to the exocyclic amine. In general, the agreement between the X-ray crystal structure of PhIP and its theory-derived counterpart in vacuo is within the combined experimental-theoretical uncertainty. The C-N bond to the exocyclic amine and the neighboring C=N imidazole bond are exceptions. This is attributed to the combined neglect of the crystal environment, waters of hydration, and the lack of coplanarity between the imidazole ring and the amine group in the calculations. To address the effect of waters of hydration, additional calculations were performed to optimize the geometry of a PhIP molecule with two water molecules hydrogen-bonded to the exocyclic amine. The resulting C-N exocyclic amine and C=N imidazole bond lengths were closer to those obtained by X-ray diffraction. The accord between theory and experiment demonstrates the utility of applying theory to (1) accurately predict structures of PhIP metabolites and intermediates that are too labile for study by conventional structural techniques such as X-ray crystallography and (2) assist in studying the mechanisms by which PhIP and its metabolites interact with proteins and DNA.

Crystallization↗