Creatine and phosphocreatine provide an intracellular, high-energy phosphate buffering system, essential to maintain ATP levels in tissues with high energy demands. A specific plasma membrane creatine transporter (CRT) is required for the cellular uptake of creatine. This transporter is related to the gamma-aminobutyric acid (GAT) and norepinephrine (NET) transporters and is part of a large gen...

The transition from rest to intense exercise is a challenge to cellular energetics (11, 13, 15). The metabolic fuels, i.e., the sources of ATP to sustain muscular contraction, are creatine phosphate and glycogen. Two anaerobic metabolic paths, leading to ATP generation, are catalyzed by creatine kinase and by the 12 enzymes of nonoxidative glycolysis, starting from glycogen. There is now genera...

The mitochondrial outer membrane separates the intermembrane space from the cytosol. The whole exchange of metabolites, cations and information between mitochondria and the cell occurs through the outer membrane. Experimental evidence is reviewed supporting the hypothesis of dynamic ADP compartmentation within the intermembrane space. The outer membrane creates a diffusion barrier for small mol...

Three fish species with different strategies for anoxic survival (goldfish, tilapia, and common carp) were exposed to environmental anoxia (4, 3, and 1 h, respectively). The concentrations of high energy phosphate compounds and inorganic phosphate, besides the intracellular pH in the epaxial muscle were measured during anoxia and recovery by in vivo 31P NMR spectroscopy. The concentration of fr...

Equations have been derived for calculating the concentrations of ATP, ADP, and AMP in equilibrium with phosphocreatine and creatine by use of association constants for the protonated species and Mg2+ complexes of the reactants and the equilibrium constants for the AMP kinase and creatine kinase reactions. The equations have been used to calculate the expected concentrations of free ATP, ADP, a...

Despite the above caveat, the impressive new technology described by Gupta et al1 in this issue of Circulation: Cardiovascular Imaging should help to resolve a number of issues relative to the hypothesis that the failing heart is energy starved and that depressed high-energy phosphate flux through the creatine kinase (CK) system is a causative factor.2,3 It will allow longitudinal measurements ...

Analyses of nucleotides and glycolytic intermediates were performed on perchlorate extracts of blood and quick-frozen brain from rats nephrectomized 48 hr previously, and from rats infused for 6 hr with adenosine or AMP. Blood nucleotides of acutely uremic rats were normal. Uremic brain showed an increase of creatine phosphate (CP), ATP, and glucose with a corresponding decrease in creatine, AD...

Creatinuria is one of the results of vitamin E deficiency. This was first demonstrated by Morgulis and Spencer (1) on rabbits. The effectiveness of a-tocopherol in reducing the excretion of creatine to normal levels was shown by Mackenzie and McCollum (2) and has been verified by many others. The creatine lost from muscle tissue during dystrophy (3) undoubtedly accounts for the creatinuria, and...

We find lag phases exceeding 20 min in measuring creatine kinase activity, by using the kinetic creatin phosphate leads to creatine assay, in sera of some patients with carcinoma metastatic to the liver. Such long lag phases are accompanied by a decreased apparent enzyme activity. These problems are eliminated by adding sulfhydryl agents to the serum before assay, but not by adding more of such...

The behavior of oxidative phosphorylation predicted by a model for the mechanism and kinetics of cytochrome c oxidase is compared with the experimentally observed behavior during the work-to-rest transition in skeletal muscle. For both experiment and model, when work stops, the increase in creatine phosphate and decrease in creatine and inorganic phosphate concentrations ([CrP], [Cr], and [Pi])...