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Biomedical subjects

Y M Yu

Publications and source records attributed to Y M Yu.

At least 91 records · Page 5Linked to original sources
PubMed1987

Pseudomonas cepacia 3-hydroxybenzoate 6-hydroxylase: stereochemistry, isotope effects, and kinetic mechanism.

A neutral flavin semiquinone species was formed upon photoreduction of Pseudomonas cepacia 3-hydroxybenzoate 6-hydroxylase whereas no flavin radical was detected by anaerobic reduction with NADH in the presence of m-hydroxybenzoate. In the latter case, the formation of flavin semiquinone is apparently thermodynamically unfavorable. A stereospecificity for the abstraction of the 4R-position hydrogen of NADH has been demonstrated for this hydroxylase. Deuterium and tritium isotope effects were observed with (4R)-[4-2H]NADH and (4R)-[4-3H]NADH as substrates. The DV effect indicates the existence of at least one slow step after the isotope-sensitive enzyme reduction by dihydropyridine nucleotide. A minimal kinetic mechanism has been deduced on the basis of initial velocity measurements and studies on deuterium and tritium isotope effects. Following this scheme, m-hydroxybenzoate and NADH bind to the hydroxylase in a random sequence. The flavohydroxylase is reduced by NADH, and NAD+ is released. Oxygen subsequently binds to and reacts with the reduced flavohydroxylase-m-hydroxybenzoate complex. Following the formation and release of water and gentisate, the oxidized holoenzyme is regenerated. The enzyme has a small (approximately 2-fold) preference for the release of NADH over m-hydroxybenzoate from the enzyme-substrates ternary complex.

Anaerobiosis↗
PubMed1985

Quantitative aspects of glycine and alanine nitrogen metabolism in postabsorptive young men: effects of level of nitrogen and dispensable amino acid intake.

The nutritionally indispensable amino acids (IAA) alone do not maintain body nitrogen (N) balance; a source of "nonspecific" nitrogen from dispensable amino acids (DAA), such as from glycine and alanine or other N compounds, is required. However, the in vivo regulation of the metabolism of these amino acids in humans with varying nutritional states has received little study. Hence, the effects of N intake and the IAA:DAA ratio on kinetic aspects of whole-body alanine and glycine metabolism were examined in eight healthy young adult male subjects. They received an L-amino acid diet supplying N equivalent to about 1.5 g and 0.6 g protein (N X 6.25) per kilogram body weight per day. All were studies at each N level with the IAA:DAA ratio (wt/wt) of 1:1 and 1:0, each for a 7-d diet period. Constant primed, intravenous infusions of L-[1-13C]leucine together with either L-[15N]alanine (four subjects) or [15N]glycine (four subjects) were given to each subject at the end of the diet period, after an overnight fast, to determine rates of de novo whole-body alanine and glycine N synthesis. The rate of alanine synthesis was similar (P greater than 0.05) for all four diets. Glycine de novo N synthesis declined (P less than 0.01) with removal of dietary DAA, especially at the lower intake, where the mean rates [micromoles/(kilogram X hour)] were 59 and 20 for 1:1 and 1:0 ratios, respectively. The possible significance of reduced rates of glycine N synthesis for maintenance of protein nutritional status in the healthy adult is discussed.

Adult↗
PubMed1976

Localization of mesenteric hyperemia during digestion in dogs.

For localization of the site of post-prandial mesenteric hyperemia, low-fat, low-protein food was placed in either the stomach, duodenum, or jejunum while blood flow was measured in the celiac artery, superior mesenteric artery (SMA), or jejunal vein of anesthetized dogs. Distribution of flow in the jejunal wall was also measured. After intragastric placement of food, celiac arterial flow increased within 5 min and remained elevated for 30-60 min; SMA flow increased within 30 min and stayed up for at least 3 h. Intra-duodenal infusion of digested food increased SMA flow but did not alter celiac flow or flow to an isolated jejunal segment. Placement of digested food into one jejunal segment increased flow to that segment did not affect flow was localized to the mucosal layer. These studies indicate that during digestion, blood flow increases in the mucosa of the intestine when exposed to chyme and is not changed in other areas of the gastrointestinal tract. Postprandial mesenteric hyperemia induced by low-fat, low-protein food is a local phenomenon.

Animals↗
PubMed1975

Distribution of blood flow in the intestine with hypertonic glucose in the lumen.

The effects of luminal placement of 50 percent glucose solution on distribution of blood flow within the jejunal wall were studied with radioactive microspheres. Two types of spheres, 15 +/- 5 mu in diameter, were used. One was labeled with cerium- 141 (Ce- 141) and the other with strontium-85 (Sr-85). They were injected sequentially to test for reproducibility of the results. These two types of spheres gave similar results qualitatively and quantitatively. Luminal placement of 50 percent glucose increased total blood flow to the jejunal wall but the increase occurred mainly in the mucosal layer. The flow to the submucosa or muscularis-serosa was not altered. This increased mucosal flow was attenuated by prior exposure of the mucosa to a local anesthetic, dibucaine. It is suggested that the increased intestinal blood flow that occurs in the experimental dumping syndrome is confined to the mucosa of the intestine and is mediated by mechanisms that can be inhibited by exposing the mucosa to a local anesthetic.

Anesthesia, Local↗