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K S Yoon

Publications and source records attributed to K S Yoon.

31 records · Page 2Linked to original sources
PubMed1998

Stress: metaplastic effects in the hippocampus.

Memory impairments, which occur regularly across species as a result of aging, disease and psychological insults (for example, stress), constitute a useful area for investigation into the neurobiological basis of learning and memory. Memory researchers have identified the hippocampus as a crucial brain structure involved in key aspects of memory formation. The most widely accepted putative mechanisms of memory storage in this structure are LTP and LTD. The hippocampus is enriched with receptors for corticosterone (a glucocorticoid hormone released in response to stress) and it plays a role in glucocorticoid negative feedback and, therefore, some hippocampal functioning might be particularly susceptible to stress. In support of this view, stress-induced modifications in learning, synaptic plasticity and endangerment of neurons have been seen in the hippocampus. Stress and glucocorticoids appear to exert a metaplastic effect through the modulation of Ca2+ levels. We propose a synaptic model that provides a conceptual scaffold to structure our understanding of the manifold actions of stress on the hippocampus. Accordingly, we suggest that stress-induced metaplasticity could disrupt Ca2+ homeostasis and thus endanger hippocampal neurons.

Animals↗
PubMed1997

Purification and characterization of pyruvate:ferredoxin oxidoreductase from Hydrogenobacter thermophilus TK-6.

Pyruvate:ferredoxin oxidoreductase was purified to electrophoretic homogeneity from an aerobic, thermophilic, obligately chemolithoautotrophic, hydrogen-oxidizing bacterium, Hydrogenobacter thermophilus TK-6, by precipitation with ammonium sulfate and fractionation by DEAE-Sepharose CL-6B, polyacrylate-quaternary amine, hydroxyapatite, and Superdex-200 chromatography. The native enzyme had a molecular mass of 135 kDa and was composed of four different subunits with apparent molecular masses of 46, 31.5, 29, and 24.5 kDa, respectively, indicating that the enzyme has an alphabetagammadelta-structure. The activity was detected with pyruvate, coenzyme A, and one of the following electron acceptors in substrate amounts: ferredoxin isolated from H. thermophilus, FAD, FMN, triphenyltetrazolium chloride, or methyl viologen. NAD, NADP, and ferredoxins from Chlorella spp. and Clostridium pasteurianum were ineffective as the electron acceptor. The temperature optimum for pyruvate oxidation was approximately 80 degrees C. The pH optimum was 7.6-7.8. The apparent Km values for pyruvate and coenzyme A at 70 degrees C were 3.45 mM and 54 microM, respectively. The enzyme was extremely thermostable under anoxic conditions; the time for a 50% loss of activity (t50%) at 70 degrees C was approximately 8 h.

Amino Acid Sequence↗
PubMed1996

Purification and characterization of 2-oxoglutarate:ferredoxin oxidoreductase from a thermophilic, obligately chemolithoautotrophic bacterium, Hydrogenobacter thermophilus TK-6.

2-Oxoglutarate:ferredoxin oxidoreductase from a thermophilic, obligately autotrophic, hydrogen-oxidizing bacterium, Hydrogenobacter thermophilus TK-6, was purified to homogeneity by precipitation with ammonium sulfate and by fractionation by DEAE-Sepharose CL-6B, polyacrylate-quaternary amine, hydroxyapatite, and Superdex-200 chromatography. The purified enzyme had a molecular mass of about 105 kDa and comprised two subunits (70 kDa and 35 kDa). The activity of the 2-oxoglutarate:ferredoxin oxidoreductase was detected by the use of 2-oxoglutarate, coenzyme A, and one of several electron acceptors in substrate amounts (ferredoxin isolated from H. thermophilus, flavin adenine dinucleotide, flavin mononucleotide, or methyl viologen). NAD, NADP, and ferredoxins from Chlorella spp. and Clostridium pasteurianum were ineffective. The enzyme was extremely thermostable; the temperature optimum for 2-oxoglutarate oxidation was above 80 degrees C, and the time for a 50% loss of activity at 70 degrees C under anaerobic conditions was 22 h. The optimum pH for a 2-oxoglutarate oxidation reaction was 7.6 to 7.8. The apparent Km values for 2-oxoglutarate and coenzyme A at 70 degrees C were 1.42 mM and 80 microM, respectively.

Amino Acid Sequence↗
PubMed1996

Purification and characterization of ferredoxin from Hydrogenobacter thermophilus strain TK-6.

Ferredoxin was purified from cells of Hydrogenobacter thermophilus strain TK-6. Purification was performed aerobically by the addition of octyl-beta-glucoside to the buffers. The purified ferredoxin had a molecular mass of 13,000 and contained a [4F3-4S] cluster. The protein had a long stretch at the N-terminal region; however, the sequence was not similar to the sequences of ferredoxins with a long stretch from Archaebacteria.

Amino Acid Sequence↗
PubMed1995

Purification and characterization of membrane-bound hydrogenase from a thermophilic hydrogen-oxidizing bacterium, Pseudomonas hydrogenothermophila strain TH-1.

A membrane-bound hydrogenase was purified aerobically by one step using a hydroxyapatite column after solubilization by acetone treatment from a thermophilic hydrogen-oxidizing bacterium, Pseudomonas hydrogenothermophila strain TH-1. The enzyme consists of two polypeptides of 63 and 31 kDa, respectively. The amino-terminal amino acid sequences of both subunits were homologous to membrane-bound type [Ni-Fe] hydrogenases from other origins. The thermostability under a hydrogen gas atmosphere is highly stable at 50 degrees C, which is the optimum temperature for the cell growth.

Amino Acid Sequence↗
PubMed1995

Bone marrow findings before and after treatment with recombinant human erythropoietin in chronic hemodialyzed patients.

The stimulating effect of rHuEPO on erythropoiesis has been shown in several studies, using bone marrow cell culture or animal models. To investigate the effect of rHuEPO on bone marrow findings in vivo, we studied the bone marrow cellularity, the myeloid: erythroid (M:E) ratio, an estimate of the number of megakaryocytes, any cytomorphologic or maturation abnormalities, and an estimate of the storage iron before and after 3 months of treatment with rHuEPO in 10 chronic hemodialyzed patients. Nine patients showed a slight or moderate decrease of erythropoiesis in bone marrow in comparison to normal bone marrow before rHuEPO treatment. The bone marrow cellularity was a mean of 28.5% and decreased in 8 out of 10 patients compared to normal values. However, megakaryopoiesis and granulopoiesis were normal. Three months of treatment with rHuEPO had increased erythropoiesis in all 10 patients, including one patient whose bone marrow proved to be normal erythropoiesis on baseline examination. The M:E ratio was significantly decreased from 4.0 +/- 1.2:1 to 2.4 +/- 1.1:1 (p < 0.005). The bone marrow cellularity was also increased in 9 patients, except in 1 patient whose specimen was inadequate for diagnosis, after 3 months of treatment with rHuEPO. On baseline examination of bone marrow, iron staining was undetectable in one, low in one, normal in 2 and high in 5 sections. According to grading, iron staining had decreased from 3.1 +/- 1.7 to 2.1 +/- 0.9 (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

Intussusception into the enteroanastomosis after Billroth II gastric resection; diagnosed by gastroscopy.

A case of retrograde intussusception (acute type) of efferent limb into Braun side-to-side jejuno-jejunal anastomosis is presented. Intussusception, though infrequent, is well recognized complication after gastric surgery. Patient was 50 year old man who was admitted with epigastric pain and abdominal mass for 6 hours. Patient had a history of total gastrectomy 2 years before admission due to stage II gastric cancer. Seven hours after admission, hematemesis developed. Emergency fiberopticgastroscopy revealed type 4 jejunogastric intussusception. Segmental resection with end-to-end reanastomosis was performed.

Humans↗
PubMed1984

Ultrastructure of the secretory epithelium, nerve fibers, and capillaries in the mouse sweat gland.

The ultrastructure of the mouse sweat gland was examined, in support of neurological studies of sweat glands and their relationships to the autonomic nervous system. It was found that the mouse sweat gland is similar to that of the rat and has only one type of secretory cell. Many nerve fibers are entwined with the secretory tubule and contain accumulations of round, clear vesicles, some microtubules, but apparently no neurofilaments. Cholinesterase is found in the clefts between nerve fibers and their ensheathing Schwann cells. The nerve fibers tend to run parallel with capillaries, but have no close association with either the capillaries or the secretory epithelium. Capillaries provide an abundant blood supply to the sweat gland and are fenestrated. The relationships between cellular elements of the sweat gland provide no direct evidence of the mechanisms involved in neurogenic sweating, although it seems likely that effector substances are diffusely distributed.

Animals↗
PubMed1979

Morphometric comparison of capillaries in muscle spindles, nerve, and muscle.

Morphometric study was performed on transverse sections of microdissected muscle spindles from rabbit tenuissimus muscles. It showed a statistically significant difference in size and structure between the intrafusal capillaries and those of extrafusal muscle. The former are larger in diameter, circumference, and area due to a proportionate increase in the number of endothelial cells. Vesicles within spindle endothelial cells are fewer, mitochondrial counts are greater, but in proportion to the increased number of endothelial cells, intercellular junctions are tight and pericyte coverage is greater. The basement membrane around endothelial cells and pericytes is thicker and more often multilayered. The endoneurial capillaries of tenuissimus intramuscular nerve are morphologically identical to intrafusal capillaries. The similarity of the capillaries of spindles to those in brain suggests that a blood-nervous system barrier extends from brain into the peripheral nerves and muscle spindles.

Animals↗
PubMed1975

Human muscle spindles: fine structure of the primary sensory ending.

The primary sensory innervation of muscle spindles obtained by muscle biopsy of normal human volunteers was studied with the light and electron microscopes. The parent IA sensory fibre branched 4-6 times, became unmyelinated for 25-30 mum, then formed sensory terminals on each nuclear bag and chain intrafusal muscle fibre. The first 4--5 mum of the unmyelinated segment is believed to be an encoder zone because the plasmalemma was undercoated by a dense granular layer similar to that under other membranes where action potentials originate. A reconstruction from micrographs of serial longitudinal sections showed that the primary sensory ending on a nuclear bag fibre is an irregular coil with branches and varicose swellings. The terminals contain central aggregates of microfilaments often surrounded by mitochondria, small numbers of vesicles, cisterns and tubular profiles. The latter merge with the plasma membrane. Junctional complexes between the plasma membranes of the terminals and intrafusal muscle resemble fascia adherns and are postulated to act as attachment plaques. These could contribute to the transduction process by incresing the degree of distortion of the terminal's membrane when stretch is applied to the spindle. A mechanism is described which could account for some of the differences in sensitivity of the primary and secondary sensory endings.

Humans↗
PubMedDate not supplied

Permeability of muscle spindle capillaries and capsule.

The permeability of capillaries in rabbit muscle spindles, intramuscular nerves, and extrafusal muscle to intraaortically infused horseradish peroxidase (HRP) was studied. The permeability of the capsule cells of the muscle spindles was also examined. Immediately following the infusion of HRP, most extrafusal capillaries contained a dense accumulation of HRP reaction product, which began to escape into the surrounding extracellular space within 2-3 min. In contrast, the concentration of HRP in the intrafusal and endoneurial capillaries was much lower than that in extrafusal capillaries, and HRP was never found outside the former vessels. In addition, HRP never completely penetrated through the spindle capsule from the extracellular into the periaxial space, although it was regularly found between the outer two or three layers of capsule cells. The results indicate that the permeability characteristics of the muscle spindle capillaries and capsule to the tracer protein HRP are very similar to those of capillaries in peripheral nerve.

Animals↗