Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: HUMANGGP:009336 (ATPase)
 59,826 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. Formycin triphosphate (FTP), a fluorescent analogue of ATP, is a substrate for (Na+ + K+)-ATPase (ATP phosphohydrolase, EC 3.6.1.3), with properties similar to those of ATP. 2. FTP and formycin diphosphate (FDP) bind to the enzyme with high affinity and, on binding, the nucleotide fluorescence is enhanced 3-4-fold. It is therefore possible, with a stopped-flow fluorimeter, to measure the rates of binding and release of FTP and FDP under conditions in which turnover does not occur. 3. When the enzyme-FTP complex is exposed to conditions permitting turnover (Mg2+, Na+ +/- K+), changes in fluorescence occur which can be explained by supposing that they reflect the interconversion of states with or without bound nucleotides. A rapid fall in fluorescence, that we attribute to the rapid release of FDP from newly phosphorylated enzyme, is followed by a steady state in which low fluorescence suggests that little nucleotide is bound. Eventually, exhaustion of FTP allows rebinding of FDP to the enzyme, which is signalled by a rise in fluorescence. 4. The estimated rate of FDP release from newly formed phosphoenzyme is unaffected by the presence of K+ (0-2 mM) or the concentration of FTP (1-20 micron). 5. Experiments with [gamma-32P]FTP show that about 1 mol of 32P is incorporated per mol of enzyme. The rate of phosphorylation of the enzyme by [gamma-32P]FTP has been measured with a rapid-mixing-and-quenching apparatus. 6. Kinetic data from the fluorescence and phosphorylation experiments show that the behaviour of the enzyme, at least at the low nucleotide concentrations employed, is consistent with the Albers-Post model, and is difficult to reconcile with models in which K+ acts at or before the step in which FDP is released during turnover.
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PMID:Elementary steps of the (Na+ + K+)-ATPase mechanism, studied with formycin nucleotides. 21 Aug 11

The influences of iron deficiency on erythrocyte spanning membrane proteins, band 3 protein and Na(+)-K(+)-ATPase, were studied in the growing rats with iron deficient anemia. The main findings were (1) reduction of band 3 and increment of band 4.1 protein. (2) diminished rate constant of pyruvate-chloride exchange (Kp:Cl.h-1) of the erythrocytes and (3) significant decrease of Na(+)-K(+)-ATPase activity only at the early stage of iron exhaustion. In addition, there was a significant negative correlation between Kp:Cl.h-1 and Na(+)-K(+)-ATPase activity both in iron deficient rats and in the controls. It is suggested that the composition and function of the erythrocyte spanning-membrane proteins for ion exchange could be affected by iron deficiency.
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PMID:Abnormalities of ion-exchange proteins of the red cell membrane in iron deficiency anemia. 131 72

Red cell membranes were isolated from blood samples obtained from athletes during exhaustive exercise on a bicycle ergometer and during the subsequent recovery period of 60 min. Plasma lactate levels were also determined. During exercise, cell membranes were progressively depleted of cholesterol and, at exhaustion, membrane cholesterol was less than 80% of the initial level. A parallel decline in Na+,K(+)-ATPase was also noted, while phospholipid reduction was around 5%. During recovery, the erythrocyte membrane cholesterol and Na+,K(+)-ATPase increased, but at a slow rate and were inversely proportional to plasma lactate content.
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PMID:Exercise-induced cholesterol depletion and Na+,K(+)-ATPase activities in human red cell membrane. 133 61

A specific complex of proteins involved in bacteriophage T4 replication has been visualized by cryoelectron microscopy as distinctive structures in association with DNA. Formation of these structures, which we term "hash-marks" for their characteristic appearance in association with DNA, requires the presence of the T4 polymerase accessory proteins (the products of T4 genes 44, 45 and 62), ATP and appropriate DNA cofactors. ATP hydrolysis by the DNA-stimulated ATPase activity of the accessory proteins is required for visualization of the hash-mark structures. If ATP hydrolysis is stopped by chelation of Mg2+, by dilution with a non-hydrolyzable ATP analogue, or by exhaustion of the ATP supply, the DNA-associated structures disappear within seconds to minutes, indicating that they have a finite and relatively short lifetime. The labile nature of the structures makes their study by more conventional methods of electron microscopy, as well as by most other structural approaches, difficult if not impossible. Addition of T4 gene 32 protein increases the number of hash-mark structures, as well as increasing the rate of ATP hydrolysis. Using plasmid DNA in either a native (supercoiled) or enzymatically modified state, we have shown that nicked or gapped DNA is required as a cofactor for hash-mark formation. Stimulation of the ATPase activity of the accessory proteins has a similar cofactor requirement. These conditions for the formation and visualization of the structures parallel those required for the action of these complexes in promoting the enzymatic activity of the T4 DNA polymerase, as well as the transcription of late T4 genes. Substructure in the hash-marks has been examined by image analysis, which reveals a variation in the projected density of the subunits comprising the structures. The three-dimensional size of the hash-marks, modeled as a solid ellipsoid, is consistent with that of the gene 44/62 protein subcomplex. Density variations suggest an arrangement of subunits, either tetragonal or trigonal, viewed from a variety of angles about the DNA axis. The hash-mark structures often appear in clusters, even in DNA that has a single nick. We interpret this distribution as the result of one-dimensional translocation of the hash-marks along the DNA after their ATP-dependent initial association with, and injection into, the DNA at nicks or gaps.
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PMID:Cryoelectron microscopic visualization of functional subassemblies of the bacteriophage T4 DNA replication complex. 153 38

In 15 conscripts, venous plasma potassium was followed during exercise on a training bicycle before and after 10 weeks of moderate physical training and a putative relationship with skeletal muscle Na,K-ATPase was evaluated. Peak plasma potassium concentration obtained at exhaustion was 6.1 +/- 0.2 and 5.6 +/- 0.2 mmol l-1 (mean +/- SEM, n = 14, P less than 0.05) before and after training, respectively. Throughout the exercise period and within the first minutes of rest plasma potassium concentration was 0.2-0.5 mmol l-1 higher before than after training. Neither peak values nor peak rises in plasma potassium concentration before nor after training were correlated to the 3H-ouabain binding site (Na,K-ATPase) concentration in vastus lateralis muscle. The results indicate that net loss of potassium from the skeletal muscle pool during exercise is reduced after training, that the heart during exercise may be exposed to a smaller rise in plasma potassium concentration after training than before, and that moderate improvement of capacity to clear extracellular potassium during exercise may be due to increased activity of existing Na,K-pumps in resting skeletal muscle fibres. This may reduce muscle fatigue, increase physical performance and explain the paradoxical observation that, despite an increased catecholamine response, there is a reduced risk of cardiac events after training.
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PMID:Exercise-induced hyperkalaemia can be reduced in human subjects by moderate training without change in skeletal muscle Na,K-ATPase concentration. 196 26

The release of Ca2+ from vesicles of heavy sarcoplasmic reticulum after its accumulation due to hydrolysis of ATP, GTP, CTP, UTP or ITP has been studied using Antipyrylazo III, a metal-chromic Ca-indicator. All the studied substrates of the Ca-pump provide Ca2+ accumulation inside the heavy sarcoplasmic reticulum vesicles, the spontaneous Ca2+ outflux rate being different for different nucleoside triphosphates. It is only ATP that provides Ca-(caffeine)-induced Ca2+ release, however AMP, ADP, beta, gamma-methylene-ATP induce Ca2+ ejection in the presence of nonadenylic nucleotides. The ruthenium red (10(-7M) inhibits the induced ejection of Ca2+ from vesicles of the heavy sarcoplasmic reticulum, but does not prevent the spontaneous release of Ca2+ in the same concentrations. A conclusion is drawn that besides Ca-channels sensitive to Ca2+ and caffeine in the presence of ATP (or to AMP, ADP, beta, gamma-methylene-ATP in the presence of nonadenylic nucleotides) and possessing high sensitivity to the ruthenium red there is another pathway for Ca2+ in the heavy reticulum membranes along which its spontaneous release occurs after the substrate exhaustion. It is supposed that this release is provided by the presence of the Ca-ATPase protein.
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PMID:[Calcium release from vesicles of heavy sarcoplasmic reticulum of rabbit skeletal muscles]. 247 98

Sarcoplasmic reticulum (SR) Ca2+ uptake and Ca2+-Mg2+-ATPase activity were examined in muscle homogenates and the purified SR fraction of the superficial and deep fibers of the gastrocnemius and vastus muscles of the rat after treadmill runs of 20 or 45 min or to exhaustion (avg time to exhaustion 140 min). Vesicle intactness and cross-contamination of isolated SR were estimated using a calcium ionophore and mitochondrial and sarcolemmal marker enzymes, respectively. Present findings confirm previously reported fiber-type specific depression in the initial rate and maximum capacity of Ca2+ uptake and altered ATPase activity after exercise. Depression of the Ca2+-stimulated ATPase activity of the enzyme was evident after greater than or equal to 20 min of exercise in SR isolated from the deep fibers of these muscles. The lowered ATPase activity was followed by a depression in the initial rate of Ca2+ uptake in both muscle homogenates and isolated SR fractions after greater than or equal to 45 min of exercise. Maximum Ca2+ uptake capacity was lower in isolated SR only after exhaustive exercise. Ca2+ uptake and Ca2+-sensitive ATPase activity were not affected at any duration of exercise in SR isolated from superficial fibers of these muscles; however, the Mg2+-dependent ATPase activity was increased after 45 min and exhaustive exercise bouts. The alterations in SR function could not be attributed to disrupted vesicles or differential contamination in the SR from exercise groups and were reinforced by similar changes in Ca2+ uptake in crude muscle homogenates.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effects of exercise of varying duration on sarcoplasmic reticulum function. 252 76

Since it has been demonstrated that endurance-trained cyclists are able to synthesize glycogen during mild exercise, glycogen synthesis was investigated in non-endurance-trained males and females as well. Seven males and nine females exercised on a cycle ergometer to deplete muscle glycogen. After the exhaustive exercise and taking a muscle biopsy, the males either exercised 2.5 h at 40% of maximal work load (trial A) or rested for 2.5 h (trial B). In both trials the subjects drank a 25% maltodextrin-fructose solution. After 2.5 h of exercise or rest, a second muscle biopsy was taken for determination of glycogen and for histochemistry (ATPase and PAS). In the females glycogen synthesis was only studied during 2.5 h rest, after prior glycogen depletion. In the male subjects, during mild exercise with carbohydrate feeding muscle glycogen did not increase. During rest muscle glycogen increased in the males from 123 +/- 49 mmol/kg DW at exhaustion to 229 +/- 70 mmol/kg DW (P less than 0.001), resulting in a net increase of 42 mmol/kg DW/h. Glycogen synthesis during rest occurred both in type I and type II fibers. In the females, during 2.5 h of rest, muscle glycogen increased from 130 +/- 56 mmol/kg DW at exhaustion to 224 +/- 51 mmol/kg DW, resulting in a net increase of 37 mmol/kg DW/h. The results demonstrate that glycogen synthesis during mild exercise does not occur in non-endurance-trained athletes, whereas in the resting state glycogen synthesis in non-endurance-trained males is not different from endurance-trained cyclists. In addition, glycogen synthesis during rest is similar in males and females.
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PMID:Glycogen synthesis during exercise and rest with carbohydrate feeding in males and females. 274 28

Phosphorescence of protein tryptophan was analyzed in sarcoplasmic reticulum vesicles, and in the purified Ca2+ transport ATPase in deoxygenated aqueous solutions at room temperature. Upon excitation with light of 295 nm wavelength, the emission maxima of fluorescence and phosphorescence were at 330 nm and at 445 nm, respectively. The phosphorescence decay was multiexponential; the lifetime of the long-lived component of phosphorescence was approximately equal to 22 ms. ATP and vandate significantly reduced the phosphorescence in the presence of either Ca2+ or EGTA; ADP was less effective, while AMP was without effect. The quenching by ATP showed saturation consistent with the idea that the ATP-enzyme complex had a lower phosphorescence yield. Upon exhaustion of ATP, the phosphorescence returned to starting level. Significant quenching of phosphorescence with a decrease in phosphorescence lifetime was also caused by NaNO2, methylvinyl ketone and trichloroacetate, without effect on ATPase activity; this quenching did not show saturation and was therefore probably collisional in nature.
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PMID:Tryptophan phosphorescence of the Ca2+-ATPase of sarcoplasmic reticulum. 297 55

The purpose of this study was to examine the Ca2+-Mg2+ myofibrillar ATPase and protein composition of cardiac and skeletal muscle following strenuous activity to voluntary exhaustion. Sprague-Dawley rats (200 g) were assigned to a control and exercised group, with the run group completing 25 m.min-1 and 8% grade for 1 hour. Following activity, the myocardial Ca2+-Mg2+ myofibrillar ATPase activity -pCa relationship had undergone a rightward shift in the curve. Electrophoretic analysis revealed a change in the pattern of cardiac myofibrillar protein bands, particularly in the 38-42 Kdalton region. Enzymatic analysis of myofibrillar proteins from plantaris muscle, revealed no change in Ca2+ regulation following exercise. Electronmicrographic and electrophoretic analysis revealed extensively disrupted sarcomeric structure and a change in the ratio of several plantaris myofibrillar proteins. No difference was observed for myosin: Actin: tropomyosin ratios; however a dramatic reduction in 58 and 95 Kdalton proteins were evident. The results indicate that prolonged running is associated with similar responses in cardiac and skeletal muscle myofibrillar protein compositions. The abnormalities in myofibrillar ultrastructure may implicate force transmission failure as a factor in exercised-induced muscle damage and/or fatigue.
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PMID:Influence of exercise on cardiac and skeletal muscle myofibrillar proteins. 297 50


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