Rate Of Glutamine Oxidation Research Articles

Effects of dietary protein intake on the oxidation of glutamate, glutamine, glucose and palmitate in tissues of largemouth bass (Micropterus salmoides).

Largemouth bass (Micropterus salmoides, a carnivorous fish native to North America) prefers to utilize amino acids as energy sources rather than glucose and fatty acids. However, little is known about the nutritional regulation of substrate oxidation in the fish. Therefore, this study was conducted to determine whether the oxidation of glutamate, glutamine, glucose and palmitate in its tissues might be influenced by dietary protein intake. Juvenile largemouth bass (initial weight 18.3 ± 0.1g) were fed three isocaloric diets containing 40%, 45% and 50% protein for 8weeks. The growth performance, energy retention, and lipid retention of juvenile fish increased with increasing dietary protein levels. The rate of oxidation of glutamate by the intestine was much greater than that of glutamine, explaining why increasing the dietary protein content from 40% to 50% had no effect on the serum concentration of glutamate but increased that of glutamine in the fish. The liver of fish fed the 50% protein diet had a higher (P < 0.05) rate of glutamine oxidation than that in the 40% and 45% protein groups. In contrast, augmenting dietary protein content from 40% to 45% increased (P < 0.05) both glutamine and glutamate oxidation in the proximal intestine of the fish and renal glutamine oxidation, without changes in intestinal or renal AA oxidation between the 45% and 50% protein groups. Furthermore, the rates of glucose oxidation in the liver, kidney, and intestine of largemouth bass were decreased in response to an increase in dietary protein content from 40% to 45% and a concomitant decrease in dietary starch content from 22.3% to 15.78%, but did not differ between the 45% and 50% protein groups. The rates of oxidation of glucose in skeletal muscle and those of palmitate in all tissues (except for the kidney) were not affected by the diets. Collectively, these results indicate that the largemouth bass can regulate substrate metabolism in a tissue-specific manner to favor protein and lipid gains as dietary protein content increases from 40% to 50% and have a lower ability to oxidize fatty acids and glucose than amino acids regardless of the dietary protein intake.

PSIII-27 Dietary intakes of protein and starch affect the oxidation of nutrients in tissues of Largemouth bass

Abstract Largemouth bass (LMB, Micropterus salmoides) is a carnivorous fish. This study was conducted to test the hypothesis that dietary intakes of protein and starch affect the oxidation of nutrients in the intestine, liver, skeletal muscle and kidneys of LMB. Juvenile LMB (average initial weight = 18 g) were fed, for 8 weeks, fish meal- and soy protein concentrate-based diets containing 40%, 45% and 50% crude protein. The three isocaloric diets contained 22.3%, 15.78% and 9.2% dextrinized starch, respectively. The growth performance, energy retention, and lipid retention in LMB increased (P &amp;lt; 0.05) with increasing dietary protein levels, but the efficiency of nitrogen retention did not differ (P &amp;gt; 0.05) among the three groups of fish. Rates of oxidation of 2 mM glutamate and glutamine in the intestine were reduced (P &amp;lt; 0.05) in response to increased dietary protein intake. This adaptive metabolic change likely helps to prevent excessive production of ATP by the gut when the dietary provision of glutamate and glutamine was increased. Increasing dietary protein intake did not affect (P &amp;gt; 0.05) glutamate oxidation in the liver, kidneys or skeletal muscle, or glutamine oxidation in the muscle. In contrast, the rate of glutamine oxidation was increased (P &amp;lt; 0.05) in the liver but decreased (P &amp;lt; 0.05) in the kidneys as dietary protein intake was elevated from 40% to 50%. Rates of oxidation of 5 mM glucose were reduced (P &amp;lt; 0.05) in the liver, kidneys and intestine, but were not altered in skeletal muscle, in response to reduced starch intake. Rates of oxidation of 2 mM palmitate were reduced (P &amp;lt; 0.05) in the kidneys but were not influenced (P &amp;gt; 0.05) in the intestine, skeletal muscle or liver. We conclude that oxidation of energy substrates in LMB tissues is regulated by dietary protein and starch intake in a tissue-specific manner.

The Role of Glutamine as an Energy Source in the Developing Rat Lung

Because multiple substrates have been shown to play a role in the metabolic homeostasis of different tissues, a series of studies were initiated to examine the role of alternate substrates in the lung. In these studies, we measured rates of oxidation of glutamine, glucose, lactate and 3-hydroxybutyrate in fibroblasts isolated from d 19 fetal rat lungs by measuring the production of 14CO2 from labeled substrates and compared them with earlier studies of isolatedType II cells. The rate of glutamine oxidation was 16.04 nmol 14CO2·mg protein-1·hr-1 in the fibroblasts compared with 24.36 in Type II cells. Three-hydroxybutyrate had a rate of 10.75 in the fibroblastsand 14.9 in the Type II cells. Lactate oxidation in fibroblasts was similar to that of glutamine, with a rate of 18.49; however, in Type II cells the rate of lactate oxidation was significantly higher at 40.29. Glucose was oxidized at a rate significantly lower than the other three substrates. In the fibroblasts, that rate was 1.22 and in Type II cells it was 2.13. To examine the interactions of substrates normally found in the intracellular milieu, we measured the effect of unlabeled substrates as competitors on labeled substrate in the fibroblats, similar to our studies with Type II cells that identified multiple metabolic compartments of energy metabolism in these cell populations. Glucose, but not lactate, inhibited the oxidation of glutamine, suggesting a compartmentation of tricarboxylic acid cycle activity rather than simple dilution by glucose. Glucose and lactate had reciprocal inhibition in the Type II cells. Our data suggest at least two separate compartments in developing lung cells for substrate oxidation: one for glutamine metabolism and a second for glucose metabolism. In summary, we have documented that glutamine and other alternate substrates are oxidized preferentially over glucose for energy metabolism in the d 19 fetal rat lung.

Glutamine metabolism in a holostean (Amia calva) and teleost fish (Salvelinus namaycush).

Amino acid metabolism was examined in mitochondria from the lateral red muscle of a teleost (lake char, Salvelinus namaycush) and a nonteleost fish (bowfin, Amia calva). Isolated mitochondria oxidize a wide variety of substrates and have high respiratory control ratios. In both species, glutamine is oxidized more rapidly than any other amino acid. The rate of glutamine oxidation by bowfin mitochondria exceeds that of lake char mitochondria, and the bowfin displays correspondingly higher levels of mitochondrial phosphate-dependent glutaminase. It is suggested that amino acids in general, and glutamine in particular, are important oxidative substrates for nonteleost red muscle. The teleost red muscle, however, may rely on both glutamine and fatty acids as oxidative substrates. It appears that glutamate derived from glutamine is oxidized primarily via glutamate dehydrogenase, whereas exogenous glutamate is oxidized primarily via aspartate aminotransferase. Complete oxidation of glutamine may be accomplished in the absence of other substrates by conversion of glutamine-derived malate to pyruvate via malic enzyme. To assess the relative abilities of various tissues to synthesize and oxidize glutamine, the activities of glutamine synthetase and glutaminase were measured. The results of these studies indicate that the organization of glutamine metabolism of fish differs markedly from that in mammals.

Substrate oxidation by isolated rat brain mitochondria and synaptosomes

The rates of [6-14C]-glucose oxidation by reconstituted systems of cytosol and mitochondria or cytosol and synaptosomes were essentially the same as the rate of oxidation of [3-14C]-3-hydroxybutyrate. However, the rate of [U-14C]-glutamine oxidation by mitochondria was 2.5 times that by synaptosomes. The addition of glutamine (5 mM) caused a reduction in the rates of oxidation [6-14C]-glucose of 20% and 40% by mitochondria and synaptosomes, respectively. Conversely, the addition of glucose (5 mM) had little or no effect on the rate of [U-14C]-glutamine oxidation by either organelle. Amino-oxyacetate decreased [U-14C]-glutamine oxidation by mitochondria more than 35% but had little or no effect on the rate of glutamine oxidation by synaptosomes. When glucose (5 mM) was added to [3-14C]-3-hydroxybutyrate, the rates of oxidation by the mitochondria and synaptosomes were increased by 65% and 77%, respectively. However, in the reverse situation the addition of 3-hydroxybutyrate decreased [6-14C]-glucose oxidation by synaptosomes (35%) but did not decrease the rate by mitochondria. These results suggest that differences in the rates of substrate utilization by mitochondria and synaptosomes and differences in substrate interactions in these two subcellular organelles may contribute to metabolic compartmentation in the brain.

Glutamine oxidation by dissociated cells and homogenates of rat brain: kinetics and inhibitor studies.

The rates of [U-14C]glutamine oxidation to 14CO2 were determined under a variety of experimental conditions using whole homogenates and dissociated cells from rat brain. The pattern of glutamine oxidation by homogenates differed from that by dissociated brain cells in several respects. The rates of glutamine oxidation by dissociated brain cells showed saturation kinetics with an apparent Km of 0.30 mM. Lineweaver-Burk plots of glutamine oxidation by homogenates revealed two linear segments with two apparent Km values (0.58 mM and 3.0 mM). In the presence of aminooxyacetate, however, the Lineweaver-Burk plots for homogenates were linear with a single Km of 0.47 mM. The oxidation of glutamine by homogenates was inhibited by both rotenone and antimycin A (80-85%), as were glutamate and glucose oxidation, suggesting that a significant amount of glutamine is oxidized via the tricarboxylic acid cycle. In the presence of aminooxyacetate, glutamine oxidation was inhibited less than 40%, whereas the oxidation of glutamate was inhibited 75%; in contrast, glucose oxidation was enhanced 50%. The rates of glutamine oxidation by homogenates were highest in the presence of high levels of potassium (50 mM) and low levels of sodium (2.5 mM). Varying ionic composition, however, had little or no effect on the rates of glutamine oxidation by dissociated brain cells. Measurements of glutamine oxidation by homogenates prepared from 2-, 10-, 15-, 25-, and 90-day-old rats revealed little or no age-dependent difference. In contrast, the oxidation by dissociated brain cells from 2-day-old animals was significantly less than that obtained for animals 10 days or older (7.76 vs. 15.6 nmol/h/mg).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the oxidation of glutamine, glucose, ketone bodies and fatty acids by human diploid fibroblasts

The contribution of glutamine, glucose, ketone bodies and fatty acids to the oxidative energy metabolism of human diploid fibroblasts was studied. The rate of glutamine oxidation by fibroblasts was 98 nmol/h per mg cell protein compared to 2 nmol/h per mg cell protein or less for glucose, acetoacetate, d-3-hydroxybutyrate, octanoic acid and palmitic acid. Glucose inhibited glutamine oxidation by 85%, while the other substrates had no effect. Therefore, these cells meet their energy requirement almost solely by anaerobic glycolysis and glutamine oxidation.

Regulation of glutamine metabolism in vitro by bicarbonate ion and pH.

The effect of variations of medium pH and bicarbonate concentration on glutamine oxidation was studied in slices and mitochondria from dog renal cortex. Decreasing pH and bicarbonate concentration increased the rate of oxidation of glutamine-U-(14)C to (14)CO(2) in both slices and mitochondria, an effect comparable to the acute stimulation of glutamine utilization produced by metabolic acidosis. Decreases in the concentration of glutamate and alpha-ketoglutarate, which accompany metabolic acidosis in the intact animal, also occurred in tissue slices when pH and [HCO(3) (-)] were lowered; decrease in alpha-ketoglutarate but not in glutamate content occurred in mitochondria under these conditions. Study of independent variations of medium pH and [HCO(3) (-)] showed that simultaneous changes in both pH and [HCO(3) (-)] produced a greater effect on glutamine metabolism than did change in either of these parameters alone. The rate of glutamine oxidation was also compared in tissue preparations from pairs of litter-mate dogs with chronic metabolic acidosis and alkalosis. No significant difference in the rate of glutamine oxidation was present in mitochondria from the two sets of animals. Slices from animals with chronic metabolic acidosis consistently oxidized glutamine at a more rapid rate than slices from alkalotic dogs both at high and at low concentrations of bicarbonate in the medium. We believe this difference is a result of the same mechanism which leads to the delayed increase in ammonium excretion during induction of metabolic acidosis. The close parallel between the effects demonstrated here and the changes in ammonium production and glutamine utilization in the intact animal with metabolic acidosis suggest that the observed in vitro changes accurately represent the operation of the physiologic mechanism by which acid-base changes regulate ammonium excretion. The similarity between the changes in glutamine oxidation observed in this study and those described previously for citrate suggests that one control mechanism affects the metabolism of both citrate and glutamine. Thus, we believe that the increase in citrate clearance in metabolic alkalosis and the increase in glutamine utilization and ammonium production in metabolic acidosis reflect the operation of the same underlying biochemical mechanism. This mechanism permits changes in pH and [HCO(3) (-)] in the cellular environment to regulate the rate of mitochondrial uptake and oxidation of several physiologically important substrates.