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C Keith

Publications and source records attributed to C Keith.

14 recordsLinked to original sources
PubMed2004

Measurement of the electric form factor of the neutron at Q2=0.5 and 1.0 GeV2/c2.

The electric form factor of the neutron was determined from measurements of the d-->(e-->,e'n)p reaction for quasielastic kinematics. Polarized electrons were scattered off a polarized deuterated ammonia (15ND3) target in which the deuteron polarization was perpendicular to the momentum transfer. The scattered electrons were detected in a magnetic spectrometer in coincidence with neutrons in a large solid angle detector. We find G(n)(E)=0.0526+/-0.0033(stat)+/-0.0026(sys) and 0.0454+/-0.0054+/-0.0037 at Q(2)=0.5 and 1.0 (GeV/c)(2), respectively.

Journal Article↗
PubMed2003

Measurement of the proton spin structure function g1(x,Q2) for Q2 from 0.15 to 1.6 GeV2 with CLAS.

Double-polarization asymmetries for inclusive ep scattering were measured at Jefferson Lab using 2.6 and 4.3 GeV longitudinally polarized electrons incident on a longitudinally polarized NH3 target in the CLAS detector. The polarized structure function g(1)(x,Q2) was extracted throughout the nucleon resonance region and into the deep inelastic regime, for Q(2)=0.15-1.64 GeV2. The contributions to the first moment Gamma(1)(Q2)= integral g(1)(x,Q2) dx were determined up to Q(2)=1.2 GeV2. Using a parametrization for g(1) in the unmeasured low x regions, the complete first moment was estimated over this Q2 region. A rapid change in Gamma(1) is observed for Q2<1 GeV2, with a sign change near Q(2)=0.3 GeV2, indicating dominant contributions from the resonance region. At Q(2)=1.2 GeV2 our data are below the perturbative QCD evolved scaling value.

Journal Article↗
PubMed1992

Adrenergic receptor-mediated increase of intracellular Ca2+ concentration in isolated bovine corneal epithelial cells.

1. We determined if Ca2+ is a second messenger for adrenergic receptor-effector coupling in bovine corneal epithelial cells. 2. Methoxamine (10(-5) M) selectively increased intracellular Ca2+ concentration (Cai) by 65%. This increase was only partially suppressed through the removal of extracellular Ca2+ or pretreatment with 10(-6) M verapamil. 3. The beta-adrenergic-mediated increases in Cai were entirely dependent on extracellular Ca2+. These increases were directly elicited through stimulation of adenylate cyclase because 10(-6) M isoproterenol and the active analogues of forskolin (10(-5) M) all elevated Cai. 4. Therefore, increases in Cai serve a second messenger function for alpha-1 and beta-adrenergic receptor-effector coupling.

Adenylyl Cyclases↗
PubMed1992

Intracellular pH regulation by a Na+/H+ exchanger in cultured bovine trabecular cells.

Intracellular pH (pHi) of cultured bovine trabecular cells was measured using video-imaging techniques with a pH-sensitive intracellular fluorescent dye, BCECF. In bicarbonate-rich Ringer at pH 7.4, pHi was 7.29 +/- 0.03 (+/- SEM, n = 12 monolayers, 120 cells sampled). Exposure to 20 mM NH4Cl immediately alkalinized pHi: replacement with a Na(+)-rich solution acidified pHi before recovery to resting levels. When NH4Cl was replaced by a low Na+ solution, acidification was sustained but pHi recovery occurred after Na(+)-rich solution. A pHi of 7.11 +/- 0.02 (n = 2 monolayers, 20 cells) occurred in pH 6.8 and pHi was 7.72 +/- 0.03 (n = 2 monolayers, 20 cells) in pH 8.0. Amiloride (1 mM) acidified pHi but DIDS (1 mM) treatment, HCO3(-)-free condition, 1 mM ouabain, 50 mM K+, and 2 mM BaCl2 failed to change pHi. Hydrogen peroxide (1 mM) acidified pHi but no change occurred with 50 microM. Trabecular cells possess an Na+/H+ exchanger similar to that in other cell types.

Ammonium Chloride↗
PubMed1983

Microinjection of Ca++-calmodulin causes a localized depolymerization of microtubules.

The microinjection of calcium-saturated calmodulin into living fibroblasts causes the rapid disruption of microtubules and stress fibers in a sharply delimited region concentric with the injection site. This effect is specific to the calcium-bearing form of calmodulin; neither calcium-free calmodulin nor calcium ion at similar levels affects the cytoskeleton. If cells have previously been microinjected with calcium-free calmodulin, elevation of their intracellular calcium levels to 25 mM potentiates the disruption of microtubules throughout the cytoplasm. Approximately 400 mM free calcium is required to cause an equivalent disruption in uninjected cells. The level of calmodulin necessary to disrupt the full complement of cellular microtubules is found to be approximately in 2:1 molar ratio to tubulin dimer. These results indicate that calmodulin can be localized within the cytoplasm in a calcium-dependent manner and that it can act to regulate the calcium lability of microtubules at molar ratios that could be achieved locally within the cell. Our results are consistent with the hypothesis that calmodulin may be controlling microtubule polymerization equilibria in areas of high local concentration such as the mitotic spindle.

Animals↗
PubMed1981

The 2.5 A crystal structure of a dimeric phospholipase A2 from the venom of Crotalus atrox.

The crystal structure of the dimeric (alpha 2) phospholipase A2 from Crotalus atrox has been determined by multiple isomorphous replacement to 2.5 A resolution. A skeletal model was fit to the electron density, and the stereochemistry of the backbone was idealized. The dimeric molecule is a well defined oblate ellipsoid composed of two covalently identical subunits related by a local dyad axis which is essentially "exact" except for deviations at the periphery induced by ionic lattice contacts with neighboring dimers. As expected, the basic architecture of the individual protomers is similar to the structure of the homologous monomeric bovine enzyme (Dijkstra, B. W., Drenth, J., Kalk, K., and Vandermaalen, P. J. (1978) J. Mol. Biol. 124, 53-60). The intramolecular contact surface between the protomers is extensive and involves the catalytic and calcium-binding sites. Access to an internal cavity formed by the enclosed and abutting active center regions is quite restricted. The putative interfacial recognition surfaces of each protomer are exposed to the solvent but are on opposing surfaces of the ellipsoid, suggesting that both of these regions cannot interact with the same membrane surface simultaneously unless the membrane is distorted from planarity and/or the dimer is significantly modified.

Amino Acid Sequence↗
PubMed1980

Discussion group for posthysterectomy patients.

Hysterectomy, the second most common type of major surgery in this country, threatens the emotional and social well-being of many patients. This article not only notes some of the common problems experienced by women who undergo a hysterectomy but also describes an individual and group teaching-counseling program that included a posthysterectomy discussion group.

Adaptation, Psychological↗