The metabolism of glucose 1-phosphate and glucose 6-phosphate and their influence on the metabolism of glucose in rat-diaphragm muscle

1. The metabolism by the bovine lens of nine (14)C-labelled l-amino acids was studied. These were: alanine, aspartate, glutamate, leucine, lysine, proline, serine, tyrosine and tryptophan. 2. All were taken up by the tissue and incorporated into protein. 3. Aspartate and glutamate, although poorly taken up, were readily metabolized to CO(2). Radioactivity from glutamate was also found in glutathione, glutamine, proline and ophthalmic acid. Aspartate was converted into glutamate, glutathione, proline, alanine and lactate. 4. Alanine was largely converted into lactate, which was released into the medium, but incorporation of radioactivity into CO(2), glutamate, glutathione, aspartate and lipids also occurred. 5. Radioactivity from leucine was detected in CO(2), lipids, glutamate, glutathione, proline and glutamine. 6. Lysine was only slightly broken down by the bovine lens; radioactivity was observed in CO(2), glutamate, glutathione, proline and two unidentified compounds. 7. Proline was metabolized to glutamate from which CO(2), glutathione and glutamine were formed. Hydroxyproline in the capsule collagen was labelled. 8. Radioactivity from serine was found in CO(2), lipids, glutathione, glycine, cystine, ATP, lactate and three unidentified compounds, one of which was probably taurine. 9. Neither tyrosine nor tryptophan were metabolized by the bovine lens. 10. The ability of the lens to metabolize amino acids was also shown by measurement of NH(3) production: more NH(3) was formed when glucose was absent from the incubation medium. 11. These experiments suggest that oxidation of amino acids is a source of energy for the lens.

Section: Methodsmentioning

confidence: 99%

The metabolism of amino acids in the bovine lens. Their oxidation as a source of energy

Trayhurn

Heyningen

1973

“…[U-14C]Glucose, [U-14C] Incubation of rat brain tisue. The conditions of incubation were the same as those described by Beloff- Chain et al (1955a) and Beloff-Chain, Catanzaro, Chain, Masi & Pocchiari (1955b.…”

Section: Methodsmentioning

confidence: 99%

“…Preparation of samples for tissue-radioactivity measurements. The methods of preparation of tissue extracts after incubation and the methods of chromatography were those described by Beloff-Chain et al (1955a. The braincortex slices were removed from the Warburg vessels, blotted on filter paper and rapidly washed in three lots of Table 1.…”

Section: Methodsmentioning

confidence: 99%

Effect of triperidol on carbohydrate and amino acid metabolism in rat brain-cortex slices

Michałek

Gatti

Pocchiari

1968

1. The effect of triperidol on the metabolism of glucose, pyruvate, glutamate, aspartate and glycine was studied with rat brain-cortex slices, U-(14)C-labelled substrates and a quantitative radiochromatographic technique. 2. Triperidol at a concentration of 0.2mm decreased the oxygen uptake and the (14)CO(2) production by about 30% when glucose, pyruvate and glutamate were used as substrates, whereas no effects were observed with aspartate and glycine. 3. The drug did not alter qualitatively the metabolic pattern of the substrates. 4. Quantitatively, triperidol decreased the incorporation of (14)C from [U-(14)C]glucose and [U(14)-C]-pyruvate into glutamate, glutamine and gamma-aminobutyrate but not into lactate, alanine and aspartate. The overall utilization rates of glucose and pyruvate were decreased. The relative specific radioactivities of glutamate and aspartate were also decreased. 5. Triperidol increased the rate of disappearance of U-(14)C-labelled glutamate, aspartate and glycine from the incubation medium, and altered the distribution of their metabolites between medium and tissue. 6. No appreciable effect of triperidol on [1-(14)C]galactose disappearance was found.

“…(Nigam, 1967a) and in isolated rat diaphragm (Beloff-Chain et al 1964;Landau & Sims, 1967), glucose 6-phosphate is a poorer precursor of glycogen than glucose, although its catabolism to carbon dioxide or lactate or both exceeds that of glucose. Glucose 6-phosphate also activates glycogen synthesis from [14C]glucose in rat diaphragm (Beloff-Chain et al 1964) and in tumour cells (Nigam, 1967a) despite its being an inhibitor of mammalian hexokinase (Crane, 1962) and a diluent of label in glucose 6-phosphate formed from [14C]glucose. In other studies the rate of glycogen synthesis in the starved diabetic rat has been shown to be higher than the activity of hexokinase in the supernatant fraction of liver of these rats (Friedmann, Goodman & Weinhouse, 1967).…”

mentioning

confidence: 99%

Pathways of glycogen synthesis in Novikoff ascites-hepatoma cells

Nigam

1969

Affinity of glucose, fructose and mannose for tumour hexokinase and their rates of phosphorylation at saturation concentration have been correlated with rates of glycogen synthesis by intact tumour cells at different concentrations of the three substrates. Competition experiments with one sugar labelled and the other sugar unlabelled indicate inhibition of glycogen synthesis by the sugar with a low K(m) for hexokinase. Glycogen synthesis from glucose 1-phosphate in aged cells and from nucleoside in freshly prepared cells is stimulated by fructose and inhibited by glucose. The decrease in glycogen formation from glucose 1-phosphate by oligomycin is partially overcome by increased fructose concentrations. These results are explained by an activation of alpha-glucan phosphorylase by fructose and an inhibition of this enzyme by glucose. It is suggested that differences in localization of glucose 6-phosphate, available to the intact cell in various ways, determine its transformation into glycogen by either the UDP-glucose-alpha-glucan glucosyltransferase reaction or by the alpha-glucan phosphorylase reaction.