Search PubMed⌕ Search

Biomedical subjects

L Davenport

Publications and source records attributed to L Davenport.

30 records · Page 2Linked to original sources
PubMed1986

Anisotropy decay associated fluorescence spectra and analysis of rotational heterogeneity. 1. Theory and applications.

Individual fluorescence spectra for species in a heterogeneous system can be determined by using differences between the rotational correlation times of those components. Each spectrum derived is associated with a particular fluorescence anisotropy decay function; hence, they are anisotropy decay associated spectra (ADAS). We have previously shown [Knutson, J. R., Walbridge, D. G., & Brand, L. (1982) Biochemistry 21, 4671-4679] that a system containing different decay functions for total intensity can be resolved into constituent decay-associated spectra. ADAS extends the technique into the realm of fluorescence polarization, making use of the often disparate Brownian rotations found in heterogeneous biochemical systems. In this paper, we present the basic theory for ADAS in various heterogeneous systems and then present an example of ADAS resolving a binary mixture of macromolecules into "fast-rotor" (smaller or more mobile) and "slow-rotor" (larger or less mobile) components. They correctly superimpose spectra taken for the unmixed components. In the companion paper [Davenport, L., Knutson, J. R., & Brand, L. (1986) Biochemistry (following paper in this issue)], a specific application to a problem of importance of lipid biochemistry--e.g., the origin of the membrane probe order parameter in lipid bilayers--is presented, demonstrating the role rotational heterogeneity may play in biochemical fluorescence.

Fluorescence Polarization↗
PubMed1986

Anisotropy decay associated fluorescence spectra and analysis of rotational heterogeneity. 2. 1,6-Diphenyl-1,3,5-hexatriene in lipid bilayers.

The application of a new spectroscopic tool [Knutson, J. R., Davenport, L., & Brand, L. (1986) Biochemistry (preceding paper in this issue)] for studying rotational microheterogeneity of probe location in lipid bilayer systems is described. Anisotropy decay associated spectra are derived from experimentally obtained polarized emission components. "Early" difference spectra (IV - IH) contain contributions from both fast and slow rotors, while "late" difference spectra predominantly reflect the emission from slowly rotating fluorophores. Anisotropy decay associated spectra have been used to resolve the emission spectra of 1,6-diphenyl-1,3,5-hexatriene (DPH) imbedded within a known rotationally heterogeneous mixture of two vesicle types (L-alpha-dimyristoyllecithin and L-alpha-dipalmitoyllecithin). At 29 degrees C, diphenylhexatriene within pure dimyristoyllecithin vesicles rotates rapidly, with a small r infinity, while diphenylhexatriene in dipalmitoyllecithin vesicles exhibits a large r infinity. Spectra for diphenylhexatriene imbedded in the two vesicle types show small but significant spectral differences. A spectrum of a mixture of the two vesicle types with DPH lies between these characteristic component spectra. The spectrum extracted for "immobilized" probes in the mixture correctly overlays the dipalmitoyllecithin spectrum. Further studies have shown that diphenylhexatriene exhibits more than one emission anisotropy decay associated spectrum in vesicles of a single lipid type, when that lipid is near its phase transition temperature. Diphenylhexatriene apparently inhabits more than one rotational environment even in these "homogeneous" vesicle preparations.

Dimyristoylphosphatidylcholine↗
PubMed1986

Excited-state proton transfer of equilenin and dihydroequilenin: interaction with bilayer vesicles.

The two-state excited-state proton-transfer process for d-equilenin [d-3-hydroxyestra-1,3,-5(10),6,8-pentaen-17-one] and dihydroequilenin is found to depend both on pH and on proton acceptor concentration. Both the protonated and deprotonated forms of the excited molecule are fluorescent. As is the case for 2-naphthol, the excited-state pKa (pKa*) is substantially lower than the ground-state pKa. Fluorescence decay studies have been performed as a function of emission wavelength in aqueous solutions at pH 6.9 in the presence of acetate anion (0.1 M). At this pH, both back-reaction from the excited-state and ground-state heterogeneity are minimal. A monoexponential decay is found in the blue region of the spectrum and a biexponential decay on the red edge. The lifetimes measured across both regions are constant, with a negative preexponential term, characteristic of an excited-state reaction, evident at longer wavelengths. Decay-associated spectra (DAS), the preexponential terms associated with the measured lifetimes, have been acquired for these aqueous solutions. Equilenin and dihydroequilenin are found to adsorb to dimyristoyllecithin (DML) vesicles. Rates for excited-state proton transfer are greatly reduced when dihydroequilenin adsorbs to vesicles. The accessibility of the bound probe to acetate as a proton acceptor depends on the cholesterol content of the vesicles.

17-Ketosteroids↗
PubMed1986

EEG spectra in dyslexic and control boys during resting conditions.

We studied the resting eyes open and eyes closed EEG in carefully screened samples of 9-13-year-old dyslexic and control boys within a 2-cohort cross-validation design with repeat testing 1-3 years later. We found: no difference between groups in delta or theta activity in either cohort or in repeat testing 1-3 years later; in the dyslexics, decreased beta (19-24 c/sec) activity at bilateral central, parietal and mid-temporal leads referenced to vertex; inconsistent group differences in the alpha band: the first cohort dyslexics had lower alpha power than did the controls, but there was no group difference in the second cohort; and significant relative delta differences between groups in the first cohort, which were shown to be a statistical artifact of the use of relative power. We conclude that: dyslexia per se is not associated with increased absolute power in the delta and theta bands; lower power in the high beta band is reliably found in these samples of dyslexics without other disorders; and alpha power levels are not consistently lower in the dyslexic group.

Alpha Rhythm↗
PubMed1986

Neurometrics does not detect 'pure' dyslexics.

Thirty-eight severely dyslexic boys and 38 good readers were evaluated with neurometrics, a diagnostic procedure based on the application of numerical taxonomy to EEG spectra obtained during resting conditions, supplemented by selected evoked potential features. This procedure generates deviance scores for the EEG spectra by comparing each individual's values to those obtained from a normative population and has been reported to discriminate learning disabled children from normal controls (Ahn et al. 1980). In the present study, all subjects, dyslexic and control, passed stringent screening to assure normal intellectual, neurological, sensory and emotional status. The false positive rate obtained in our control group was comparable to that reported earlier. However, none of the deviance scores significantly discriminated dyslexics from controls; most subjects from both groups were classified as normal. Severe dyslexia per se is thus not associated with the specific neurometric abnormalities reported previously in more heterogeneous learning disabled populations.

Adolescent↗
PubMed1986

Narrative speech deficits in dyslexics.

Narrative speech of 31 dyslexics and 33 good readers was studied. Subjects were 10- to 12-year-old right-handed boys of normal intelligence, and with normal neurological status, vision, and hearing. The dyslexics used shorter communication units (independent clauses with all their modifiers), and a higher percentage of their words were noncommunications (words which are extraneous to the speaker's intended meaning). Rate of speech was the same in both groups. These findings were replicated in an independent second cohort of 21 dyslexics and 21 controls, aged 9 to 13. Our findings support theories of a general language deficit in dyslexia, and demonstrate the involvement of the previously unexamined area of narrative speech.

Adolescent↗
PubMed1985

Transverse location of the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene in model lipid bilayer membrane systems by resonance excitation energy transfer.

A fluorescent phospholipid derivative, the fluoresceinthiocarbamyl adduct of a natural phosphatidylethanolamine, has been synthesized and incorporated into sonicated single-bilayer vesicles of egg lecithin and dipalmitoyllecithin. The surface location of this probe has been confirmed by using extrinsic fluorescence quenching studies together with steady-state emission anisotropy measurements. Electronic excitation energy transfer between 1,6-diphenyl-1,3,5-hexatriene incorporated within the hydrophobic core of the bilayer and the novel derivative has been investigated to estimate the depth within the bilayer at which the former is located. Efficiencies have been measured for two different phospholipids, egg lecithin and dipalmitoyllecithin, in the latter case both above and below the phospholipid phase transition, with and without added cholesterol. The observed dependence of the transfer efficiency on the acceptor concentration was compared with that calculated according to Förster theory applied to random two-dimensional distributions of donor and acceptor molecules in parallel planes for various interplanar separations, taking into account orientational effects. The Förster R0 of about 45 A for this donor-acceptor pair is particularly well suited to such studies since it is of the order of the width of the bilayer. The experiments showed that energy-transfer spectroscopy can provide useful quantitative information as to the transverse location of diphenylhexatriene in homogeneous phospholipid bilayers and may also reflect lateral partitioning of donor or of both donor and acceptor into different phases in systems exhibiting phase separations.

Diphenylhexatriene↗
PubMed1984

Nanosecond time-resolved emission anisotropy of the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene in human amniotic fluid.

The fluorescence emission anisotropy of 1,6-diphenyl-1,3,5-hexatriene in human amniotic fluid has been studied using nanosecond time-resolved emission techniques. These studies demonstrate that the previously reported decrease in the steady state emission anisotropy, [r], with gestational age is due to a change in the rate of rotational motion of the probe. The emission anisotropy decays to a limiting value (r infinity) greater than zero, suggesting a hindered rotation of the probe, and this is independent of gestational age. The decay function for the emission anisotropy of amniotic fluids from 17, 29, 40 and 41 weeks in gestational age can be best expressed as a single exponential plus a constant term, with rotational correlation times varying from 17 ns to 2.2 ns, respectively. The zero time emission anisotropy remains approx. 0.30 for both early and late gestational times.

Amniotic Fluid↗
PubMed1976

Comparison of human and hamster mitochondrial transfer RNA. Physical properties and methylation status.

We have compared mitochondrial transfer RNA from cultured human (HeLa) and hamster(BHK) cells, giving emphasis to distinctive properties previously noted for the BHK system. Both HeLa and BHK mitochondrial tRNA sedimented slower, and had lower mobilities in "warm" acrylamide gels, than their cytoplasmic counterparts, suggesting that both mitochondrial tRNA populations have unusually loose configurations. HeLa mitochondrial tRNA was found to contain 2.8 methyl groups per 100 nucleotides compared to 8.7 for cytoplasmic, figures similar to previous BHK results. Both mitochondrial tRNA populations were notably deficient in 7-methylguanine, methylribose, and methylated pyrimidines. We propose that mitochondrial tRNA (or perhaps animal mitochondrial tRNA) constitutes a distinct evolutionary class.

Animals↗
PubMedDate not supplied

MR imaging of the aging brain: patchy white-matter lesions and dementia.

Magnetic resonance (MR) imaging studies of the brain in five elderly patients with non-Alzheimer dementia were compared with those in two groups of nondemented control subjects. Group 1 included five subjects aged 59-66; group 2 included nine subjects aged 74-81. In all of the demented patients and in three of the subjects in the older control group, MR showed diffuse, patchy white-matter lesions. A rating scale was used to grade the severity of the changes. The results suggest a higher incidence of white-matter lesions in elderly patients with non-Alzheimer dementia and in cognitively normal elderly with advancing age.

Age Factors↗