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Biomedical subjects

T M Chen

Publications and source records attributed to T M Chen.

136 records · Page 8Linked to original sources
PubMed1971

Photosynthetic CO(2) Fixation Products and Activities of Enzymes Related to Photosynthesis in Bermudagrass and Other Plants.

After a 5-second exposure of illuminated bermudagrass (Cynodon dactylon L. var. ;Coastal') leaves to (14)CO(2), 84% of the incorporated (14)C was recovered as aspartate and malate. After transfer from (14)CO(2)-air to (12)CO(2)-air under continuous illumination, total radioactivity decreased in aspartate, increased in 3-phosphoglyceric acid and alanine, and remained relatively constant in malate. Carbon atom 1 of alanine was labeled predominantly, which was interpreted to indicate that alanine was derived from 3-phosphoglyceric acid. The activity of phosphoenolpyruvate carboxylase, alkaline pyrophosphatase, adenylate kinase, pyruvate-phosphate dikinase, and malic enzyme in bermudagrass leaf extracts was distinctly higher than those in fescue (Festuca arundinacea Schreb.), a reductive pentose phosphate cycle plant. Assays of malic enzyme activity indicated that the decarboxylation of malate was favored. Both malic enzyme and NADP(+)-specific malic dehydrogenase activity were low in bermudagrass compared to sugarcane (Saccharum officinarum L.). The activities of NAD(+)-specific malic dehydrogenase and acidic pyrophosphatase in leaf extracts were similar among the plant species examined, irrespective of the predominant cycle of photosynthesis. Ribulose-1, 5-diphosphate carboxylase in C(4)-dicarboxylic acid cycle plant leaf extracts was about 60%, on a chlorophyll basis, of that in reductive pentose phosphate cycle plants.We conclude from the enzyme and (14)C-labeling studies that bermudagrass contains the C(4)-dicarboxylic acid cycle and that pyruvate-phosphate dikinase does not exist exclusively in C(4)-dicarboxylic acid cycle plants, and we propose that in C(4)-dicarboxylic acid cycle plants the transfer of carbon from a dicarboxylic acid to 3-phosphoglyceric acid involves a decarboxylation reaction and then a refixation of carbon dioxide by ribulose-1, 5-diphosphate carboxylase.

Journal Article↗
PubMed1969

Photosynthetic Activity of Chloroplasts Isolated From Bermudagrass (Cynodon dactylon L.), a Species With a High Photosynthetic Capacity.

Chloroplasts have been isolated from bermudagrass (Cynodon dactylon L.) leaves and assayed for photophosphorylation and electron transport activity. These chloroplasts actively synthesize adenosine triphosphate during cyclic electron flow with phenazine methosulfate and noncyclic electron flow concurrent with the reduction of such Hill oxidants as nicotinamide adenosine dinucleotide phosphate, cytochrome c, and ferricyanide. Apparent Km values for the cofactors of photophosphorylation have been determined to be 5 x 10(-5) M for phosphate and 2.5 x 10(-5) M for adenosine diphosphate. The influence of light intensity on photophosphorylation has been studied and the molar ratio of cyclic to noncyclic phosphorylation calculated. It is concluded that the high photosynthetic capacity of bermudagrass leaves probably could be supported by the photophosphorylation capacities indicated in these chloroplast studies and the anomalous lack of data in chlorolast studies on the production of sufficient reductant for CO(2) assimilation at high light intensities has been noted.

Journal Article↗
PubMedDate not supplied

Thermospray liquid chromatographic-mass spectrometric analysis of castanospermine-related alkaloids in Castanospermum australe.

Crude sample solution prepared from the seeds of Castanosperum australe was fractionated by preparative liquid chromatography. The fractions thus obtained were subsequently analyzed by means of thermospray liquid chromatography-mass spectrometry (tsp lc-ms). Under the conditions employed, castanospermine [1], 6-epi-castanospermine [2], australine [3], 3,8-di-epi-alexine [4], and fagomine [5] could be separated and detected. The possible structures of other castanospermine-related alkaloids found in the crude sample solution are also discussed.

Alkaloids↗
PubMedDate not supplied

Phase I clinical trial of curcumin, a chemopreventive agent, in patients with high-risk or pre-malignant lesions.

Curcumin (diferuloylmethane), a yellow substance from the root of the plant Curcuma longa Linn., has been demonstrated to inhibit carcinogenesis of murine skin, stomach, intestine and liver. However, the toxicology, pharmacokinetics and biologically effective dose of curcumin in humans have not been reported. This prospective phase-I study evaluated these issues of curcumin in patients with one of the following five high-risk conditions: 1) recently resected urinary bladder cancer; 2) arsenic Bowen's disease of the skin; 3) uterine cervical intraepithelial neoplasm (CIN); 4) oral leucoplakia; and 5) intestinal metaplasia of the stomach. Curcumin was taken orally for 3 months. Biopsy of the lesion sites was done immediately before and 3 months after starting curcumin treament. The starting dose was 500 mg/day. If no toxicity > or = grade II was noted in at least 3 successive patients, the dose was then escalated to another level in the order of 1,000, 2,000, 4,000, 8,000, and 12,000 mg/day. The concentration of curcumin in serum and urine was determined by high pressure liquid chromatography (HPLC). A total of 25 patients were enrolled in this study. There was no treatment-related toxicity up to 8,000 mg/day. Beyond 8,000 mg/day, the bulky volume of the drug was unacceptable to the patients. The serum concentration of curcumin usually peaked at 1 to 2 hours after oral intake of crucumin and gradually declined within 12 hours. The average peak serum concentrations after taking 4,000 mg, 6,000 mg and 8,000 mg of curcumin were 0.51 +/- 0.11 microM, 0.63 +/- 0.06 microM and 1.77 +/- 1.87 microM, respectively. Urinary excretion of curcumin was undetectable. One of 4 patients with CIN and 1 of 7 patients with oral leucoplakia proceeded to develop frank malignancies in spite of curcumin treatment. In contrast, histologic improvement of precancerous lesions was seen in 1 out of 2 patients with recently resected bladder cancer, 2 out of 7 patients of oral leucoplakia, 1 out of 6 patients of intestinal metaplasia of the stomach, I out of 4 patients with CIN and 2 out of 6 patients with Bowen's disease. In conclusion, this study demonstrated that curcumin is not toxic to humans up to 8,000 mg/day when taken by mouth for 3 months. Our results also suggest a biologic effect of curcumin in the chemoprevention of cancer.

Adult↗
PubMedDate not supplied

Pharmacokinetics and metabolism of vigabatrin following a single oral dose of [14C]vigabatrin in healthy male volunteers.

14C-labeled vigabatrin (50 microCi), an antiepileptic drug, was administered to six healthy male volunteers as a single oral dose containing 1500 mg of vigabatrin to determine the disposition profile of 14C and parent drug, and to investigate the metabolism of vigabatrin in humans. Vigabatrin was well tolerated by all subjects. There were no clinically important changes in any clinical laboratory parameter. Plasma concentration profiles of both 14C and vigabatrin exhibited biexponential decay. AUC, Cmax, Tmax, and terminal phase t1/2, for 14C were consistently greater than vigabatrin (248.2 vs. 176.0 micrograms-hr/ml; 48.8 vs. 42.8 micrograms/ml; 0.7 vs. 0.6 hr; and 9.5 vs. 7.7 hr, respectively). Mean renal clearance, oral clearance, and volume of distribution for 14C was consistently lower than vigabatrin (1.20 vs. 1.45 ml/min/kg; 1.26 vs. 1.77 ml/min/kg; and 1.01 vs. 1.18 liters/kg, respectively). The mean percentage of recovery of 14C in urine was higher than vigabatrin (95.4 vs. 82.0%). The mean percentage of recovery of 14C in feces was 1.0%. Concentration ratios of 14C showed that vigabatrin distributes into red blood cells at a concentration of 30-80% of that in plasma. The concentration of vigabatrin in saliva was approximately 10% of that in the plasma. The main radioactive component eliminated in the urine was vigabatrin. Two minor urinary metabolites (< 5% of total dose) of vigabatrin were detected using liquid scintillation counting of HPLC eluant fractions. One urinary metabolite was identified by thermospray-LC/MS as the lactam metabolite of vigabatrin.

Administration, Oral↗