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D Canet

Publications and source records attributed to D Canet.

32 records · Page 2Linked to original sources
PubMed1996

Ca2+ translocation across sarcoplasmic reticulum ATPase randomizes the two transported ions.

Cytoplasmic Ca2+ dissociation is sequential, and the Ca2+ ions bound to the nonphosphorylated ATPase are commonly represented as superimposed on each other, so that the superficial Ca2+ is freely exchangeable from the cytoplasm, whereas the deeper Ca2+ is not. Under conditions where ADP-sensitive phosphoenzyme accumulates (leaky vesicles, 5 degrees C, pH 8, 300 mM K+), luminal Ca2+ dissociation is sequential as well, so that the representation of two superimposed Ca2+ ions still holds on the phosphoenzyme, with the superficial Ca2+ facing the lumen freely exchangeable and the deeper Ca2+ blocked by the superficial Ca2+. Under the same conditions, we have investigated whether a prebuilt Ca2+ order is maintained during membrane translocation. Starting from a prebuilt order on the cytoplasmic side, we showed that the Ca2+ ions cannot be identified after translocation to the luminal side. The same result was obtained starting from a prebuilt order on the luminal side and following the luminal to cytoplasmic translocation. We conclude that the two Ca2+ ions are mixed during ATP-induced phosphorylation as well as during ADP-induced dephosphorylation.

Adenosine Diphosphate↗
PubMed1996

Skeletal muscle beta-adrenoreceptors and phosphate metabolism abnormalities in heart failure in rats.

To investigate the mechanisms leading to skeletal muscle metabolic abnormalities in chronic heart failure (CHF), we studied phosphate metabolism and skeletal muscle beta-adrenoreceptors (beta-AR) in rats 12-14 wk after coronary ligation (CL). We performed 31P magnetic resonance spectroscopy in the gastrocnemius muscle during motor activity produced by electrical stimulation (5 Hz). The initial slope of phosphocreatine (PCr) depletion was higher in the CL rats compared with sham-operated rats (Pi/PCr/time: 0.211 +/- 0.045 vs. 0.113 +/- 0.029; P < 0.05). During recovery, both PCr resynthesis rate and maximal rate of oxidative ATP synthesis were reduced threefold in the CL rats compared with controls (11 +/- 2 vs. 37 +/- 7 mmol.l-1.min-1, P < 0.04; and 20 +/- 3 vs. 79 +/- 18 mmol.l-1.min-1, P < 0.03, respectively). There were no significant differences either for the skeletal muscle density (13 +/- 6 vs. 15 +/- 3 fM/mg) or for the affinity (0.244 +/- 0.149 vs. 0.246 +/- 0.146 nM) of beta-AR between the two groups. This study showed that, although in moderate CHF skeletal muscle metabolic abnormalities can be demonstrated, these changes could not be explained by skeletal muscle beta-adrenergic receptor alterations in this experimental model.

Animals↗
PubMed1995

Lumenal Ca2+ dissociation from the phosphorylated Ca(2+)-ATPase of the sarcoplasmic reticulum is sequential.

Once two radioactive Ca2+ coming from the cytoplasm are bound to the transport sites of the nonphosphorylated ATPase, excess EGTA induces rapid dissociation of both ions, whereas excess nonradioactive Ca2+ only reaches one of the two bound Ca2+. This difference has been explained assuming that the two Ca2+ sites are in a single file channel in which the superficial Ca2+ is freely exchangeable from the cytoplasm, whereas the deeper Ca2+ is exchangeable only when the superficial site is vacant. The same experiment was done using phosphorylated ATPase to determine whether Ca2+ dissociation toward the lumen is sequential as well. Under conditions that allow ADP-sensitive phosphoenzyme to accumulate (leaky vesicles, 5 degrees C, pH 8, 300 mM KC1), we found the same two pools of Ca2+. Excess EGTA induced dissociation of both ions together with dephosphorylation. Excess nonradioactive Ca2+ induced the exchange of half the radioactive Ca2+ without any effect on the phosphoenzyme level. Our results show a close similarity between the transport sites of the nonphosphorylated and the phosphorylated enzymes, although the orientation, affinities, and dissociation rate constants are different.

Animals↗
PubMed1995

Dipolar local field measurements from indirect observation of 1H nuclei via cross-polarization 13C nuclear magnetic resonance spectroscopy.

An extension of the exploitation of a simple pulse sequence designed for indirect observation of 1H nuclei through 13C resonances is presented. It is shown that by using this pulse sequence under conditions of rapid magic-angle rotation and coherent energy transfer between directly bonded protons and carbons, an insight into the local dipolar interactions is available in typical organic solids.

Calcium↗
PubMed1995

Measurement of Hartmann-Hahn cross-polarization dynamics with quenching of proton T1 rho relaxation dependence.

A simple modification of the standard cross-polarization method designed for quenching the proton T1 rho dependence when studying polarization transfer is presented. It is demonstrated that by using this simple procedure, new and subtle details of cross-polarization dynamics, previously hidden by the T1 rho(1H) effect, can be observed in dipolar-coupled spin systems.

Magnetic Resonance Spectroscopy↗
PubMed1988

Carbohydrate and Amino Acid Metabolism in the Ectomycorrhizal Ascomycete Sphaerosporella brunnea during Glucose Utilization : A C NMR Study.

Nuclear magnetic resonance spectroscopy was utilized to study the metabolism of [1-(13)C]glucose in mycelia of the ectomycorrhizal ascomycete Sphaerosporella brunnea. The main purpose was to assess the biochemical pathways for the assimilation of glucose and to identify the compounds accumulated during glucose assimilation. The majority of the (13)C label was incorporated into mannitol, while glycogen, trehalose and free amino acids were labeled to a much lesser extent. The high enrichment of the C1/C6 position of mannitol indicated that the polyol was formed via a direct route from absorbed glucose. Randomization of the (13)C label was observed to occur in glucose and trehalose leading to the accumulation of [1,6-(13)C]trehalose and [1,6-(13)C]glucose. This suggests that the majority of the glucose carbon used to form trehalose was cycled through the metabolically active mannitol pool. The proportion of label entering the free amino acids represented 38% of the soluble (13)C after 6 hours of continuous glucose labeling. Therefore, amino acid biosynthesis is an important sink of assimilated carbon. Carbon-13 was incorporated into [3-(13)C]alanine and [2-(13)C]-, [3-(13)C]-, and [4-(13)C]glutamate and glutamine. From the analysis of the intramolecular (13)C enrichment of these amino acids, it is concluded that [3-(13)C]pyruvate, arising from [1-(13)C]glucose catabolism, was used by alanine aminotransferase, pyruvate dehydrogenase, and pyruvate carboxylase (or phosphoenolpyruvate carboxykinase). Intramolecular (13)C labeling patterns of glutamate and glutamine were similar and are consistent with the operation of the Krebs cycle. There is strong evidence for (a) randomization of the label on C2 and C3 positions of oxaloacetate via malate dehydrogenase and fumarase, and (b) the dual biosynthetic and respiratory role of the citrate synthase, aconitase, and isocitrate dehydrogenase reactions. The high flux of carbon through the carboxylation (presumably pyruvate carboxylase) step indicates that CO(2) fixation is an important component of the carbon metabolism in S. brunnea, and it is likely that this anaplerotic role is particularly prevalent during NH(4) (+) assimilation. The most relevant information resulting from this investigation is (a) the occurrence of the mannitol cycle, (b) a large part of the trehalose pool is synthesized after the cycling of glucose-carbon through the mannitol cycle, and (c) pyruvate (or phosphoenolpyruvate) carboxylation plays an important role in the primary metabolism of glucose-fed mycelia.

Journal Article↗
PubMed1985

C Nuclear Magnetic Resonance Study of Mannitol Cycle and Trehalose Synthesis during Glucose Utilization by the Ectomycorrhizal Ascomycete Cenococcum graniforme.

(13)C nuclear magnetic resonance spectroscopy has been used to follow the utilization of glucose for the synthesis of carbohydrates in the ectomycorrhizal ascomycete Cenococcum graniforme. The fate of (13)C label was analyzed in vivo and in mycelial extracts. The major carbohydrates produced from [1-(13)C]glucose and [6-(13)C]glucose were mannitol and trehalose. Mannitol was mainly synthesized via a direct route from glucose. Scrambling of the (13)C label was observed to occur in trehalose during glycolysis. From the analysis of the scrambling patterns, it is concluded that the mannitol cycle was operative and that a large part of the carbon of glucose was used to form trehalose after cycling through the mannitol pool. The activities of NAD-mannitol-l-P dehydrogenase (EC 1.1.1.17) and NADP-mannitol dehydrogenase (EC 1.1.1.138), which participate in the mannitol cycle relative to the activity of glycolytic enzymes, provide evidence that the cycle is important for NADPH production.

Journal Article↗
PubMed1984

In Vivo Natural-Abundance C Nuclear Magnetic Resonance Studies of Living Ectomycorrhizal Fungi : Observation of Fatty Acids in Cenococcum graniforme and Hebeloma crustuliniforme.

Natural-abundance (13)C nuclear magnetic resonance spectroscopy has been used to study intact mycelia of the ectomycorrhizal fungi Cenococcum graniforme (Ascomycetes) and Hebeloma crustuliniforme (Basidiomycetes). A number of sharp resonances are observed in living fungi. These signals primarily arise from fatty acyl chains and carbohydrate nuclei. The spectra are interpreted in terms of relative concentrations of the major fatty acids present in the fungal triglycerides. The small line width of fatty acids (mainly oleic, linoleic, and palmitic acids) resonances and spin-lattice relaxation time are indicative of fast rotational reorientations and are consequently thought to arise from fatty acyl chains in fat droplets. We were able to locate the site of lipids accumulation within mycelia using light microscopy and histological staining. Many lipid droplets were observed in mycelia of both species.These results suggest that fatty acids droplets could be involved in carbon storage and metabolism from ectomycorrhizal fungi.

Journal Article↗
PubMed1983

Frequency dependence of water proton longitudinal NMR relaxation times in mouse tissues around the freezing transition.

Water proton longitudinal NMR relaxation times were measured in various tissues of healthy and tumor-bearing mice. Measurements were performed as a function of the Larmor frequency nu in the range 6-90 MHz, and at two temperatures (theta + and theta -) bracketing the 'freezing transition', at which the major part of the water signal disappears. At both temperatures, 1/T1 behaves according to: 1/T1 = A/square root nu + B A and B are obtained at theta + and theta -, and yield the proportion of bound water, which is convincingly identified with non-freezable water. The proportions found lie around 6% for tumors and 12% for other tissues. Discrimination between tissues via T1 is demonstrated to be essentially due to the bound water proportion. Bound water on the one hand and free water on the other hand behave similarly in all tissues including tumors. The activation energy for free water is found to be identical to that of pure water, although relaxation times are markedly different. It is noticed that determining the bound water proportion by signal intensity measurements at theta + and theta - is less reliable than by the T1 method.

Animals↗
PubMed1982

Frequency dependence of water proton longitudinal nuclear magnetic relaxation times in mouse tissues at 20 degrees C.

We have measured the proton longitudinal relaxation times of tissue water of healthy and tumor-bearing mice as a function of the Larmor frequency in the range 6.7 to 90 MHz. These data can be rationalized according to T1-1 = A v -1/2 +B, where A and B are constants specific to the tissue species. We present an interpretation of this frequency dependence within the Fast Exchange Two States model. It is shown that involving a distribution of correlation times for water proton-proton interaction does not yield consistent results, whereas a physically meaningful translational diffusion model pertinent to the dipolar interaction between water protons and macromolecules protons leads to the required frequency dependence. Essentially tissues would differ by the 'bound' versus 'free' proportion, or by structural properties of cells, rather than by the time-scales governing water motion.

Animals↗
PubMed1981

NMR proton longitudinal relaxation times in tissues of the tumour-bearing C3H mouse studied as a function of frequency.

Because of progress in NMR imaging techniques that open the feasibility of detecting cancer by recording water protein relaxation times, it is essential to elucidate the origin of the changes of this parameter by careful studies on animals. Water proton longitudinal relaxation times were measured in vitro between 7 and 90 MHz for several tissue samples of C3H male and female mice, controls and tumor-bearing. We showed that tumor and other tissues of cancerous animals gave higher T1 values than the same tissues of controls, but that this "systemic" effect of cancer was superimposed to larger genetical T1 changes. We draw conclusions for an optimum frequency around 10 MHz, giving maximum of contrast between tumor and other tissues. According to a two-site model of water in tissues, we found the "bound" water compartment to be smaller in tumor, or, preferably, that the magnitude of the water-protein interaction was smaller there.

Animals↗
PubMed1980

Nitrogen-15 chemical shifts and 1J15N1H of some tripeptides measured at the natural abundance level.

An indirect method combining double-resonance and difference spectroscopy has been used in order to determine 15N chemical shifts and 1J15N1H in glutathione (in H2O at pH 3 and under the same conditions with urea added) and in a series of tripeptides of the type Gly-Gly-L-X (with X = Glu, His, Val, Leu, and Ile) in H2O and at two different pH values. This method has proved to be very efficient as long as the NH proton is not in exchange. The chemical shifts are shown to depend on the considered sequence and especially on the substituent in the gamma position. One-bond couplings show some systematic trends which have been tentatively interpreted in terms of the s character of the N-H bond. Although these latter parameters seem of potential utility in structural determinations, additional data will be needed in order to rationalize their variations.

Amino Acid Sequence↗