ATP synthesis and storage (original) (raw)
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ATP Signaling in Skeletal Muscle
Exercise and Sport Sciences Reviews, 2014
Tetanic electrical stimulation releases adenosine triphosphate (ATP) from muscle fibers through pannexin-1 channels in a frequency-dependent manner; extracellular ATP activates signals that ultimately regulate gene expression and is able to increase glucose transport through activation of P2Y receptors, phosphatidylinositol 3-kinase, Akt, and AS160. We hypothesize that this mechanism is an important link between exercise and the regulation of muscle fiber plasticity and metabolism.
Archives of Biochemistry and Biophysics, 2002
Extracellular ATP acts as a signal that regulates a variety of cellular processes via binding to P2 purinergic receptors (P2 receptors). We herein investigated the effects and signaling pathways of ATP on glucose uptake in C 2 C 12 skeletal muscle cells. ATP as well as P2 receptor agonists (ATP-c S) stimulated the rate of glucose uptake, while P2 receptor antagonists (suramin) inhibited the stimulatory effect of ATP, indicating that P2 receptors are involved. This ATP-stimulated glucose transport was blocked by specific inhibitors of Gi protein (pertusiss toxin), phospholipase C (U73122), protein kinase C (GF109203X), and phosphatidylinositol (PI) 3-kinase (LY294002). ATP stimulated PI 3-kinase activity and P2 receptor antagonists blocked this activation. In C 2 C 12 myotubes expressing glucose transporter GLUT4, ATP increased basal and insulin-stimulated glucose transport. Finally, ATP facilitated translocation of GLUT1 and GLUT4 into plasma membrane. These results together suggest that cells respond to extracellular ATP to increase glucose transport through P2 receptors. Ó
ATP Synthase: Structure, Function and Inhibition
Biomolecular Concepts
Oxidative phosphorylation is carried out by five complexes, which are the sites for electron transport and ATP synthesis. Among those, Complex V (also known as the F1F0 ATP Synthase or ATPase) is responsible for the generation of ATP through phosphorylation of ADP by using electrochemical energy generated by proton gradient across the inner membrane of mitochondria. A multi subunit structure that works like a pump functions along the proton gradient across the membranes which not only results in ATP synthesis and breakdown, but also facilitates electron transport. Since ATP is the major energy currency in all living cells, its synthesis and function have widely been studied over the last few decades uncovering several aspects of ATP synthase. This review intends to summarize the structure, function and inhibition of the ATP synthase.
International journal of molecular sciences, 2008
Complete details of the thermodynamics and molecular mechanisms of ATP synthesis/hydrolysis and muscle contraction are offered from the standpoint of the torsional mechanism of energy transduction and ATP synthesis and the rotation-uncoiling-tilt (RUT) energy storage mechanism of muscle contraction. The manifold fundamental consequences and mechanistic implications of the unified theory for oxidative phosphorylation and muscle contraction are explained. The consistency of current mechanisms of ATP synthesis and muscle contraction with experiment is assessed, and the novel insights of the unified theory are shown to take us beyond the binding change mechanism, the chemiosmotic theory and the lever arm model. It is shown from first principles how previous theories of ATP synthesis and muscle contraction violate both the first and second laws of thermodynamics, necessitating their revision. It is concluded that the new paradigm, ten years after making its first appearance, is now perfe...
Regulation of the mitochondrial ATP-synthase in health and disease
Molecular genetics and metabolism, 2003
In most tissues the mitochondrial ATP-synthase plays a central role by synthesizing the bulk of ATP. According to the classical theory of respiratory control, flux through this enzyme is solely determined by substrate (ADP) concentration while the enzyme has a fixed capacity. However, in different cell types such as rat cardiomyocytes and neurons, dog heart, human fibroblasts, and skeletal and heart muscle from children, it has been shown that active regulation of the mitochondrial ATP-synthase in response to cellular energy demand exists. For example, in rat cardiomyocytes the mitochondrial ATP-synthase activity is down-regulated in response to anoxia or mitochondrial uncoupling. By this mechanism cellular ATP is conserved, as under these conditions the ATP-synthase would work in reverse and hydrolyze ATP. When cardiomyocytes are stimulated to contract, ATP-synthase activity is up-regulated in line with the increased energy demand. Preincubation of the cardiomyocytes with positive inotropic substances results in further up-regulation of the ATP-synthase. By blocking calcium transport, it has been shown that the up-regulation of the enzyme is calcium-dependent. On a molecular level, up-regulation is probably mediated by the calcium-binding inhibitor protein (CaBI) and down-regulation via the inhibitor protein IF 1. The ATP-synthase system is disturbed under several pathophysiological conditions. First, mutations can cause a primary defect in the mitochondrial ATP-synthase (respiratory chain defect). Furthermore, secondary defects of the ATP-synthase occur. In rat models abnormalities of ATP-synthase can be detected in different types of cardiomyopathy/heart hypertrophy. The changes are reversible in response to treatment of the heart diseases. Abnormalities of the ATPsynthase system can be observed in fibroblasts from patients with neuronal ceroidlipofuscinoses. Toxic metabolites accumulating in methylmalonic acidurias can inhibit ATP-synthase. When neurons are incubated with 3-OH glutarate-a substance accumulating in glutaric aciduria I-as a model for glutaric aciduria I, ATP-synthase activity is compromised. This lack of energy may lead to Ôslow onsetÕ excitotoxicity and finally cell death. Cells can be rescued by adding creatine to the incubation medium. In D D-2-hydroxyglutaric aciduria, inhibition of the ATP-synthase has been observed.
From ATP to PTP and Back: A Dual Function for the Mitochondrial ATP Synthase
Circulation research, 2015
Mitochondria not only play a fundamental role in heart physiology but are also key effectors of dysfunction and death. This dual role assumes a new meaning after recent advances on the nature and regulation of the permeability transition pore, an inner membrane channel whose opening requires matrix Ca(2+) and is modulated by many effectors including reactive oxygen species, matrix cyclophilin D, Pi (inorganic phosphate), and matrix pH. The recent demonstration that the F-ATP synthase can reversibly undergo a Ca(2+)-dependent transition to form a channel that mediates the permeability transition opens new perspectives to the field. These findings demand a reassessment of the modifications of F-ATP synthase that take place in the heart under pathological conditions and of their potential role in determining the transition of F-ATP synthase from and energy-conserving into an energy-dissipating device.
Compartmentalized ATP synthesis in skeletal muscle triads
Biochemistry, 1992
Isolated skeletal muscle triads contain a compartmentalized glycolytic reaction sequence catalyzed by aldolase, triosephosphate isomerase, glyceraldehyde-3-phosphate dehydrogenase, and phosphoglycerate kinase. These enzymes express activity in the structure-associated state leading to synthesis of ATP in the triadic junction upon supply of glyceraldehyde 3-phosphate or fructose 1,6-bisphosphate. ATP formation occurs transiently and appears to be kinetically compartmentalized, i.e., the synthesized ATP is not in equilibrium with the bulk ATP. The apparent rate constants of the aldolase and the glyceraldehyde-3phosphate dehydrogenase/phosphoglycerate kinase reaction are significantly increased when fructose 1,6bisphosphate instead of glyceraldehyde 3-phosphate is employed as substrate. These observations suggest that fructose 1,6-bisphosphate is especially effectively channelled into the junctional gap. The amplitude of the ATP transient is decreasing with increasing free [Ca*+] in the range of 1 nM to 30 FM. In the presence of fluoride, the ATP transient is significantly enhanced and its declining phase is substantially retarded. This observation suggests utilization of endogenously synthesized ATP in part by structure associated protein kinases and phosphatases which is confirmed by the detection of phosphorylated triadic proteins after gel electrophoresis and autoradiography. Endogenous protein kinases phosphorylate proteins of apparent M, 450 000, 180 000, 160 000, 145 000, 135 000, 90 000, 54 000, 5 1 000, and 20 000, respectively. Some of these phosphorylated polypeptides are in the M, range of known phosphoproteins involved in excitation-contraction coupling of skeletal muscle, which might give a first hint at the functional importance of the sequential glycolytic reactions compartmentalized in triads.
ATP synthesis at physiological nucleotide concentrations
Scientific Reports, 2019
synthesis of Atp by the F 1 F 0 Atp synthase in mitochondria and most bacteria is energized by the proton motive force (pmf) established and maintained by respiratory chain enzymes. Conversely, in the presence of Atp and in the absence of a pmf, the enzyme works as an Atp-driven proton pump. Here, we investigate how high concentrations of ATP affect the enzymatic activity of the F 1 F 0 Atp synthase under high pmf conditions, which is the typical situation in mitochondria or growing bacteria. Using the ATP analogue adenosine 5′-O-(1-thiotriphosphate) (ATPαS), we have developed a modified luminescence-based assay to measure Atp synthesis in the presence of millimolar Atp concentrations, replacing an assay using radioactive nucleotides. In inverted membrane vesicles of E. coli, we found that under saturating pmf conditions, ATP synthesis was reduced to ~10% at 5 mM ATPαs. this reduction was reversed by ADp, but not p i , indicating that the Atp/ADp ratio controls the Atp synthesis rate. our data suggests that the ATP/ADP ratio ~30 in growing E. coli limits the ATP synthesis rate to ~20% of the maximal rate possible at the applied pmf and that the rate reduction occurs via product inhibition rather than an increased Atp hydrolysis rate.
Biochemistry, 2007
The plasma membrane calcium ATPase (PMCA) reacts with ATP to form acid-stable phosphorylated intermediates (EP) that can be measured using (γ-32 P)ATP. However, the steady-state level of EP at [ATP] higher than 100 µM has not yet been studied due to methodological problems. Using a microscale method and a purified preparation of PMCA from human red blood cells, we measured the steady-state concentration of EP as a function of [ATP] up to 2 mM at different concentrations of Mg 2+ , both at 4 and 25°C. We have measured the Ca 2+-ATPase activity (V) under the same conditions as those used for phosphorylation experiments. While the curves of ATPase activity vs [ATP] were well described by the Michaelis-Menten equation, the corresponding curves of EP required more complex fitting equations, exhibiting at least a high-and a low-affinity component. Mg 2+ increases the apparent affinity for ATP of this latter component, but it shows no significant effect on its high-affinity one or on the Ca 2+-ATPase activity. We calculated the turnover of EP (k pEP) as the ratio V/EP. At 1 mM Mg 2+ , k pEP increases hyperbolically with [ATP], while at 8 µM Mg 2+ , it exhibits a behavior that cannot be explained by the currently accepted mechanism for ATP hydrolysis. These results, together with measurements of the rate of dephosphorylation at 4°C, suggest that ATP is acting in additional steps involving the interconversion of phosphorylated intermediates during the hydrolysis of the nucleotide.
Diabetologia, 2010
Aims/hypothesis Insulin resistance in skeletal muscle is linked to mitochondrial dysfunction in obesity and type 2 diabetes. Emerging evidence indicates that reversible phosphorylation regulates oxidative phosphorylation (OxPhos) proteins. The aim of this study was to identify and quantify site-specific phosphorylation of the catalytic beta subunit of ATP synthase (ATPsyn-β) and determine protein abundance of ATPsyn-β and other OxPhos components in skeletal muscle from healthy and insulin-resistant individuals. Methods Skeletal muscle biopsies were obtained from lean, healthy, obese, non-diabetic and type 2 diabetic volunteers (each group n=10) for immunoblotting of proteins, and hypothesis-driven identification and quantification of phosphorylation sites on ATPsyn-β using targeted nanospray tandem mass spectrometry. Volunteers were metabolically characterised by euglycaemic-hyperinsulinaemic clamps. Results Seven phosphorylation sites were identified on ATPsyn-β purified from human skeletal muscle. Obese individuals with and without type 2 diabetes were characterised by impaired insulin-stimulated glucose disposal rates, and showed a ∼30% higher phosphorylation of ATPsyn-β at Tyr361 and Thr213 (within the nucleotidebinding region of ATP synthase) as well as a coordinated downregulation of ATPsyn-β protein and other OxPhos components. Insulin increased Tyr361 phosphorylation of ATPsyn-β by ∼50% in lean and healthy, but not insulinresistant, individuals. Conclusions/interpretation These data demonstrate that ATPsyn-β is phosphorylated at multiple sites in human skeletal muscle, and suggest that abnormal site-specific phosphorylation of ATPsyn-β together with reduced content of OxPhos proteins contributes to mitochondrial dysfunction in insulin resistance. Further characterisation of phosphorylation of ATPsyn-β may offer novel targets of treatment in human diseases with mitochondrial dysfunction, such as diabetes.