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Biomedical subjects

K Chen

Publications and source records attributed to K Chen.

At least 523 records · Page 29Linked to original sources
PubMed1988

Oxidation of hydroxylamines to nitroxide spin labels in living cells.

In the presence of oxygen, cells can oxidize hydroxylamines, which are the products of the reduction of nitroxides in cells, back to nitroxides. Lipid-soluble hydroxylamines are oxidized much more rapidly than water-soluble ones, and most of this oxidation is inactivated by heat or trichloroacetic acid, indicating that the principal mechanism is enzyme-linked. The rates of oxidation of some lipophilic hydroxylamines are comparable to the rates of reduction of the corresponding nitroxides. Hydroxylamines formed by reduction of aqueous soluble nitroxides are not oxidized by cells, except for slight oxidation of some pyrrolidine derivatives. The latter is due to autoxidation. The kinetics of oxidation of reduced lipid-soluble nitroxides are all first-order with respect to hydroxylamines, regardless of the position of the nitroxide group along the carbon backbone, indicating that the oxidation occurs within the membrane. The oxidation of hydroxylamines in cells in inhibited by cyanide but not by antimycin A or SKF-525A. We also describe an effective method to oxidize hydroxylamines and follow this reaction; the method is based on the use of perdeuterated [15N]Tempone.

Affinity Labels↗
PubMed1988

The major aeroallergens in Guangxi, China.

Over a 2-year period we have identified pollen grains from 48 families of grasses, as well as mould spores and mite particles during air sampling in Guangxi Province. The major aeroallergens were Artemisia, Moraceae and Euophoribiacea, and the spores of Aspergillus, Penicillinum, Cephalosporium and Helminthosporium. Mites were probably also one of the major outdoor aeroallergens. Our investigations also included inspection of the vegetation of the geographical area involved, as well as skin testing on 774 subjects using extracts of 37 aeroallergens. We believe that this work has provided fundamental information on seasonal allergy in Southern China and South-east Asia.

Air Pollution↗
PubMed1987

Further evidence that the pigment in the Dubin-Johnson syndrome is not melanin.

The pigment in the Dubin-Johnson syndrome (DJS) is shown unequivocally not to be a typical melanin or closely related polymer. In electron spin resonance (ESR) studies of DJS pigment from a hepatoma, it is shown that, unlike true melanins, the pigment associated with the DJS syndrome has no free radical in the absence of light. Exposure to even low levels of visible light over a broad frequency range induces a free radical in the DJS pigment. Previous studies did not appreciate the sensitivity to light of this pigment and therefore erroneously concluded that the DJS pigment had a permanent free radical. The light induced ESR signal in DJS tissue has spectroscopic properties that differ significantly from any known melanins. The pigment is not extracted by lipophilic solvents and is centrifuged down at 50,000g, but not at 5,000g.

Carcinoma, Hepatocellular↗
PubMed1987

Sarcoidosis of the stomach.

A 25-year-old housewife presented with an 8-month history of epigastric pain, vomiting and weight loss. This was found to be due to sarcoidosis of the stomach. Her condition improved remarkably on steroids.

Adult↗
PubMed1987

[[Age composition and population cycles]].

The author attempts to correlate the endogenous population cycle with changes in age composition by examining population trends in Taiwan. "It is argued that while the size of parental cohort is related to the size of offspring cohort by the renewal process, fluctuations in size are correspondingly transmitted and averaged time after time." The concepts of population cycles as a key factor in population change is also examined. (SUMMARY IN ENG)

Age Distribution↗
PubMed1987

Comparison of a noninvasive measurement of optic nervehead mechanical compliance with an invasive method.

We have postulated that abnormal mechanical support of the optic nervehead at the level of the lamina cribrosa could be the precursor of glaucomatous damage. Recent studies have shown deformations of the lamina cribrosa to be among the earliest changes in glaucoma. To evaluate the support of the nervehead, we have developed a noninvasive optical method to measure the optic nervehead compliance, namely, the displacement of the optic nervehead induced by an artificial increase in intraocular pressure. To test the validity of the method, we have compared noninvasive measurements obtained in post-mortem enucleated human eyes with those recorded using an invasive technique. Both methods had a reproducibility better than 6 microns and induced no damage capable of interfering with the results. The displacements measured by both methods were similar, thus indicating that our optical method is capable of measuring bulk motion of the optic nervehead. Our results were identical with those obtained by other authors using a third method. The data obtained also established the normal range of optic nervehead displacements induced by a range of intraocular pressure increments.

Adult↗
PubMed1987

Double immunoenzyme staining method for analysis of tissue and blood lymphocyte subsets with monoclonal antibodies.

Double immunoenzymatic method for sequential staining with two different monoclonal murine antibodies and two different enzymes was shown to be useful in defining hematopoietic cell subpopulations in human tissues and blood. The method allows for the identification, localization, and enumeration in the same section of distinct cell populations. Air-dried smears of cell mixtures can be stained. The optimal sequence of enzymes/substrates was: horseradish peroxidase/3-amino-9-ethylcarbazole followed by the alkaline phosphatase-anti-alkaline phosphatase complex/naphthol AS-MX phosphate. Red-and blue-colored reaction products are easy to view in a light microscope. Combinations of two different mouse monoclonal antibodies or of a mouse monoclonal antibody and polyclonal antiserum made in rabbits or goats can be sequentially applied to the same section or smear thus facilitating a definition of the distribution of two cell populations reactive with these antibodies. The relative distribution patterns in tissues of cells bearing distinctive antigens are important in studies of cellular differentiation and of human pathogenetic processes including neoplasia and transplant rejection.

Antibodies, Monoclonal↗
PubMed1986

Hypoxia-sensitive NMR contrast agents.

The rate of reduction of nitroxides is shown to be more rapid in hypoxic cells. The rate of reduction and the effect of hypoxia on the reduction rate vary for different nitroxides. These findings indicate that it may be feasible to develop in vivo NMR contrast agents that selectively will indicate areas of hypoxia and thereby aid in the detection of disease processes such as neoplasia, ischemia, and inflammation.

Animals↗
PubMed1986

Ultranarrowband searches for extraterrestrial intelligence with dedicated signal-processing hardware.

Multichannel spectroscopy with millihertz resolution constitutes an attractive strategy for a microwave search for extraterrestrial intelligence (SETI), assuming the transmission of a narrow-band radiofrequency beacon. Such resolution matches the properties of the interstellar medium, and the necessary receiver Doppler corrections provide a high degree of interference rejection. We have constructed a frequency-agile swept receiver with an 8,388,608-channel spectrum analyzer, on-line signal recognition, and multithreshold archiving. A search of 250 Sun-like stars at 1.4 and 2.8 GHz has been carried out with the Arecibo 305-m antenna, and a meridian transit search of the northern sky is in progress at the Harvard-Smithsonian 26-m antenna. Successive spectra of 400 kHz at 0.05 Hz resolution are searched for features characteristic of an intentional narrowband beacon transmission. These spectra are centered on guessable ("magic") frequencies (such as the 21-cm hydrogen hyperfine line), referenced successively to the local standard of rest, the galactic barycenter, and the cosmic blackbody rest frame.

Astronomy↗