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Query: EC:3.6.4.1 (myosin ATPase)
 1,140 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Control of mitochondrial respiration depends on ADP availability to the F1-ATPase. An electrochemical gradient of ADP and ATP across the mitochondrial inner membrane is maintained by the adenine nucleotide translocase which provides ADP to the matrix for ATP synthesis and ATP for energy-dependent processes in the cytosol. Mitochondrial respiration is responsive to the cytosolic phosphorylation potential, ATP/ADP.Pi which is in apparent equilibrium with the first two sites in the electron transport chain. Conventional measures of free adenine nucleotides is a confounding issue in determining cytosolic and mitochondrial phosphorylation potentials. The advent of phosphorus-31 nuclear magnetic resonance (P-31 NMR) allows the determination of intracellular free concentrations of ATP, creatine-P and Pi in perfused muscle in situ. In the glucose-perfused heart, there is an absence of correlation between the cytosolic phosphorylation potential as determined by P-31 NMR and cardiac oxygen consumption over a range of work loads. These data suggest that contractile work leads to increased generation of mitochondrial NADH so that ATP production keeps pace with myosin ATPase activity. The mechanism of increased ATP synthesis is referred to as 'stimulus-response-metabolism' coupling. In muscle, increased contractility is a result of interventions which increase cytosolic free Ca2+ concentrations. The Ca2+ signal thus generated increases glycogen breakdown and myosin ATPase in the cytosol. This signal is concomitantly transmitted to the mitochondria which respond to small increases in matrix Ca2+ by activation of Ca2+-sensitive dehydrogenases. The Ca2+-activated dehydrogenase activities are key rate-controlling enzymes in tricarboxylic acid cycle flux, and their activation by Ca2+ leads to increased pyridine nucleotide reduction and oxidative phosphorylation.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Control of mitochondrial respiration in muscle. 305 Apr 50

The time course of changes of inorganic phosphate (Pi) and phosphocreatine (PCr) was studied during and after brief isometric tetanic contractions using phosphorus nuclear magnetic resonance on isolated semitendinosus muscles of the bullfrog at 4 degrees C. We followed essentially the method of Dawson, Gadian and Wilkie and the signal-to-noise ratio was improved by using many muscles. Immediately following the relaxation of contraction, the fall of PCr was not sufficient to account for the Pi released. The level of PCr remained unaltered, or decreased further, in the early post-contractile period. The amount of Pi that appeared without PCr splitting was similar to the amount of myosin sites (0.3 mmol kg-1 muscle) irrespective of the duration of contraction. The post-contractile utilization of PCr was strongly temperature dependent. It was prolonged at 1 degree C, whereas it almost disappeared at 10 degrees C. When the filament overlap was much reduced by stretching the muscles the phenomenon became undetectable. All these results have indicated that the post-contractile utilization of PCr is closely associated with the actin-myosin ATPase cycle.
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PMID:Time-resolved 31P nuclear magnetic resonance studies on isometric contraction of frog skeletal muscle. 326 89

The purpose of this study was to examine the relationships between the relative contents of phosphocreatine (PCr), inorganic phosphate (Pi), beta-adenosine triphosphate (ATP), and transverse relaxation time (T2) with fiber composition, which determined histochemically in the human skeletal muscle. The vastus lateralis muscles of 28 volunteers were subjected to phosphorus nuclear magnetic resonance (31P NMR) spectroscopy, magnetic resonance imaging (MRI) and muscle biopsy. Muscle fibers were divided into type I and type II fibers using myosin ATPase stain. A wide range of fiber composition levels were observed in the subjects (27.3-74.6% type I fibers). The PCr/ATP, Pi/ATP and (PCr + Pi)/ATP ratios were positively related to the percentage of type II fibers (r = 0.695, p < 0.001, r = 0.429, p < 0.05 and r = 0.773, p < 0.001, respectively). There was no correlation between fiber composition and the PCr/Pi ratio (r 0.127, n.s.) or intracellular pH (r = 0.305, n.s.). Moreover, no correlation was found between T2 and fiber type (r = 0.144, n.s.). These results suggest that 31P NMR can detect the differences in relative content of phosphates between type I and type II fibers, thereby noninvasively evaluating fiber composition in human skeletal muscle.
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PMID:Relationships between fiber composition and NMR measurements in human skeletal muscle. 884 27