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L Lee

Publications and source records attributed to L Lee.

At least 343 records · Page 19Linked to original sources
PubMed1982

Analysis and formation of nitrosamines in the human intestine.

The method employed for nitrosamine analysis gave high recovery values and did not produce artefactual nitrosamines. Nitrosation reactions are not catalysed by the microbial ecosystem of human feces. Rapid loss of nitrate and nitrite in feces also precludes nitrosamine formation, unless very high concentrations of precursors are present. These concentrations are not physiological and it is therefore unlikely that N-nitroso compounds form in the lower gastrointestinal tract of man.

Feces↗
PubMed1981

Proton nuclear magnetic resonance determination of the sequential ytterbium replacement of calcium in carp parvalbumin.

The substitution of the paramagnetic lanthanide ion ytterbium for the calcium ions bound to the CD and EF sites of carp parvalbumin results in a series of 1H NMR resonances which are shifted far outside the envelope of the 1H NMR spectrum of the diamagnetic form of the protein. Titration of Ca2+-saturated parvalbumin with ytterbium (YB3+) demonstrate that Yb3+ sequentially replaces the two bound calcium ions of the protein. Analysis of the 1H NMR data yields the relative affinities of the two sites (CD and EF) for ytterbium with respect to calcium. The dissociation constants for ytterbium are then calculated to be KYb3+CD equals (4-7) x 10(-10) M and KYb3+EF equals (2-6) x 10(-10) M from the known dissociation constants for calcium [Haiech, J., Derancourt, J., Pechere, J.-F., & Demaille, J. G. (1979) Biochemistry 18, 2752-2758]. The approximate equality of these constants is verified by Yb3+ titrations of apoparvalbumin.

Animals↗
PubMed1981

Accessory proteins for DNA polymerase alpha activity with single-strand DNA templates.

Three forms of DNA polymerase alpha [DNA nucleotidyltransferase (DNA-directed), EC 2.7.7.7] were partially purified from the combined nuclear extract and postmicrosomal supernatant solution of synchronized HeLa cells. These enzymes, designated DNA polymerases alpha 1, alpha 2, and alpha 3, on the basis of their order of elution from DEAE-Bio-Gel, differ in their abilities to utilize single-strand DNA templates. DNA polymerase alpha 2 has equal catalytic activities with activated and single-strand DNAs as template-primers. DNA polymerase alpha 1 has only partial catalytic activity with single-strand DNA templates, and DNA polymerase alpha 3 is essentially inactive with this template. Successive steps of hydrophobic affinity chromatography and phosphocellulose chromatography of DNA polymerase alpha 2 resolved the polymerase alpha activity and two protein factors (C1 and C2) that are required for its catalytic activity with a DNA template-primer that contains extended single-strand regions. In the absence of the factors, DNA polymerase alpha activity is measurable with activated but not single-strand DNA templates. In the presence of the C1 and C2 factors DNA polymerase alpha activity with single-strand DNA templates is restored to about 75% of the catalytic activity of DNA polymerase alpha 2 with this template.

DNA, Single-Stranded↗
PubMed1981

Influence of age on reactivity of 1-way mixed lymphocyte cultures in young chickens.

A reproducible 1-way mixed lymphocyte culture (MLC) assay was used to study the ontogeny of MLC in N, P, RPRL-72 and RPRL-63 strains of chickens. The chicks were progeny of specific-pathogen-free and lymphoid leukosis virus-free parents and grown in common isolators. When cells were from responder and stimulator chickens of the same age, the RPRL-72 chickens cells responded by 8 wk, whereas cells from chickens of the other 3 strains did not respond significantly until after 14 wk of age. In MLC with 6- and 32-wk-old RPRL-72 and N birds, the age of the responder was not crucial. However, young or old N birds responded extremely well to old 72 stimulator cells, whereas young 72 cells stimulated no, or minimal, response. Thus the age of the stimulator cell is vary important in chicken MLC and appears to depend upon the responder chicken strain.

Aging↗
PubMed1981

Absence of volatile nitrosamines in human feces.

Using a method for nitrosamine analysis that gives high recovery values and that is free from artifactual synthesis of nitrosamines, we have shown that human feces do not contain volatile nitrosamines (detection limit, 0.1 to 0.5 microgram/kg). We also showed that nitrosation reactions are not catalyzed by fecal organisms. Following a 2-day anaerobic incubation of feces with either a secondary amine (dimethylamine, dipropylamine, or morpholine) or nitrite, no nitrosamine was formed. When the amine and nitrite were added together, nitrosamine was formed, but at a level of 2 to 20% of that formed in autoclaved feces under the same conditions. Nitrosamines were stable following anaerobic incubation with feces for up to 4 days. These results suggest that fecal organisms inhibit the chemical formation of nitrosamines instead of catalyzing it. When morphine and nitrate were added together, nitrosomorpholine was formed. Morpholine nitrosates so rapidly that it intercepts nitrite formed by the action of nitrate reductase before the nitrite can be further reduced. However, very high concentrations of morphine and nitrate, which are far from the conditions in normal feces, were required to form measurable nitrosomorpholine. We may conclude that N-nitroso compounds are unlikely to be formed in any significant amounts in the human colon.

Feces↗
PubMed1980

Nuclear magnetic resonance determination of metal-protn distances in the EF site of carp parvalbumin using the susceptibility contribution to the line broadening of lanthanide-shifted resonances.

The substitution of the paramagnetic lanthanide ion ytterbium for the calcium ion in the EF calcium binding site of carp parvalbumin results in a series of 1H NMR resonances which are shifted well outside of the envelope of the 1H NMR spectrum of the diamagnetic form of the protein. The line broadening of these shifted resonances has been measured as a function of 1H NMR frequency between 200 and 400 MHz, and the spin-lattice relaxation rates have been measured at 270 MHz. The analysis of the relaxation rates based upon the theories of Vega & Fiat [Vega, A. J., & Fiat, D. (1976) Mol. Phys. 31, 347-355] and Guéron [Guéron, M. (1975) J. Magn. Reson. 19, 58-66] indicates that a major contribution to the line widths comes from the novel susceptibility relaxation mechanism and that the metal to proton distances can be directly calculated from this contribution.

Animals↗
PubMed1980

Strategies for the uses of lanthanide NMR shift probes in the determination of protein structure in solutio. Application to the EF calcium binding site of carp parvalbumin.

The homologous sequences observed for many calcium binding proteins such as parvalbumin, troponin C, the myosin light chains, and calmodulin has lead to the hypothesis that these proteins have homologous structures at the level of their calcium binding sites. This paper discusses the development of a nuclear magnetic resonance (NMR) technique which will enable us to test this structural hypothesis in solution. The technique involves the substitution of a paramagnetic lanthanide ion for the calcium ion which results in lanthanide induced shifts and broadening in the 1H NMR spectrum of the protein. These shifts are sensitive monitors of the precise geometrical orientation of each proton nucleus relative to the metal. The values of several parameters in the equation relating the NMR shifts to the structure are however known as priori. We have attempted to determine these parameters, the orientation and principal elements of the magnetic susceptibility tensor of the protein bound metal, by studying the lanthanide induced shifts for the protein parvalbumin whose structure has been determined by x-ray crystallographic techniques. The interaction of the lanthanide ytterbium with parvalbumin results in high resolution NMR spectra exhibiting a series of resonances with shifts spread over the range 32 to -19 ppm. The orientation and principal elements of the ytterbium magnetic susceptibility tensor have been determined using three assigned NMR resonances, the His-26 C2 and C4 protons and the amino terminal acetyl protons, and seven methyl groups; all with known geometry relative to the EF calcium binding site. The elucidation of these parameters has allowed us to compare the observed spectrum of the nuclei surrounding the EF calcium binding site of parvalbumin with that calculated from the x-ray structure. A significant number of the calculated shifts are larger than any of the observed shifts. We feel that a refinement of the x-ray based proton coordinates will be possible utilizing the geometric information contained in the lanthanide shifted NMR spectrum.

Animals↗
PubMed1980

Vasovasostomy: a comparison of macroscopic and microscopic techniques at one institution.

During a 5-year period between 1973 and 1977, 87 patients underwent vasovasostomy to correct postvasectomy sterility. Sixty-one patients had single-layer macroscopic reanastomoses and 26 patients had two-layer microscopic reanastomoses. Patency rates of 90% and 96% and pregnancy rates of 46% and 54% for the macroscopic and microscopic techniques were achieved.

Adult↗
PubMed1980

Influence of the age of erythrocytes on their insulin receptors.

Specific binding of 125I-insulin to erythrocyte receptors increased linearly with reticulocyte count in routine blood specimens from hospitalized patients. Specific binding as high as 30-35% is observed in patients with reticulocyte counts in the range of 20-25% compared with 9.0 +/- 0.5% specific binding in healthy control subjects with normal reticulocyte counts. It is concluded that care must be exercised in interpreting elevations of specific 125I-insulin binding to erythrocyte receptors as due to specific disease processes without considering how the disease itself may alter mean erythrocyte age at the time of sampling.

Erythrocyte Aging↗
PubMed1980

Primary gram negative pneumonia in adults in Papua New Guinea.

A retrospective review of gram-negative bacteraemia in Papua New Guinean adults revealed four cases of primary gram negative pneumonia over a two-year period. Patients with primary gram negative pneumonia constituted less than 1% of all pneumonias admitted to the medical ward. Pseudomonas pseudomallei, Haemophilus influenzae and Klebsiella pneumoniae were the aetiologic agents. Three of four patients died following a fulminant course. It is concluded that primary gram-negative pneumonia in Papua New Guinea is rare but carries a high mortality.

Adult↗