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Biomedical subjects

C K Chang

Publications and source records attributed to C K Chang.

138 records · Page 8Linked to original sources
PubMed1973

Synthesis of the myoglobin active site.

A simple heme-imidazole compound, having the same geometry as the heme-imidazole complex in myoglobin, has been synthesized. This compound, ferropyrroporphyrin-N-[3-(1-imidazolyl)propyl]amide, reversibly binds oxygen in the solid state or when dissolved in a polystyrene film. These results suggest that the principal factors governing reversible oxygen binding are the electronic nature of the base (imidazole), neighboring-group effects of the basic group, and immobilization of the heme group.

Binding Sites↗
PubMed1972

Antiviral action of camptothecin.

At a concentration of 10 mum, camptothecin inhibited vaccinia deoxyribonucleic acid (DNA) synthesis in HeLa cells. Inhibition of viral DNA synthesis was observed when the drug was added before infection or at 1 or 2 hr after infection. Inhibitory effects of camptothecin on vaccinia DNA synthesis could be reversed, even after exposure to the alkaloid for 2 hr. Viral DNA, isolated from vaccinia-infected, camptothecin-treated cells, displayed an altered sedimentation constant after alkaline sucrose density gradient centrifugation. Incorporation of uridine into vaccinia messenger ribonucleic acid was inhibited by camptothecin, but the activity of ribonucleic acid polymerase, as tested in isolated vaccinia cores, was not affected by the drug. Camptothecin had essentially no effect on replication of poliovirus in HeLa cells.

Antiviral Agents↗
PubMedDate not supplied

Molecular recognition with C-clamp porphyrins: synthesis, structural, and complexation studies.

Porphyrin-based molecular clefts equipped with a strategically positioned carboxylic group have been synthesized. These ditopic porphyrins exhibit excellent binding affinity for many neutral substrates. X-ray structures of a porphyrin-water inclusion complex and a Zn(porphyrin)-methanol complex reveal how the carboxylic group interacts with substrates via H-bonding. Multipoint recognition is demonstrated in the differential binding of 1,2,3- versus 1,2,4-triazole, suggesting the possible use of such receptors to separate heterocyclic bases.

Crystallography, X-Ray↗
PubMedDate not supplied

Inhibition of the dopamine system in rat amygdala attenuates the picrotoxin-induced locomoter hyperactivity and hypertension.

The aim of the present study was to investigate whether picrotoxin-induced locomotor hyperactivity and hypertension can be inhibited by dopaminergic inhibition in rat amygdala. Locomotor activity was detected using a modularized infrared light matrix system in freely moving rats. In anaesthetized rats, blood pressure was measured while dopamine release was detected using in vivo voltammetry with carbon fibre electrodes. Systemic administration of picrotoxin (1-4 mg/kg) increased both locomotor activity (including horizontal motion, vertical motion and total distance travelled) and the number of turnings (both clockwise and anticlockwise), but inhibited postural freezing. The locomotor hyperactivity induced by systemic administration of picrotoxin was mimicked by direct injection of a small dose (1-3 micro g in 1.0 micro L) of picrotoxin into the amygdala. In vivo voltammetry data revealed that systemic administration of picrotoxin increased the release of dopamine in the amygdala of rat brain accompanied by hypertension. Local injection of kainic acid into the paramedian reticular nucleus (PRN) of the medulla oblongata decreased both the spontaneous release of dopamine in the amygdala and spontaneous levels of locomotor activity in rats. Furthermore, the picrotoxin-induced locomotor hyperactivity, hypertension and increased amygdaloid dopamine release were all suppressed following chemical stimulation of the PRN with kainic acid. Blockade of dopamine receptors with systemic or intra-amygdaloid injection of haloperidol (a dopamine receptor antagonist) significantly attenuated the picrotoxin-induced locomotor hyperactivity and hypertension. These results demonstrate that picrotoxin-induced hyperactivity and hypertension involve an increase in amygdaloid dopamine transmission that can be modulated by ascending projections from the PRN in the medulla oblongata.

Amygdala↗