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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The rates of the ATPase [EC 3.6.1.3] reaction of the H-meromyosin-F-actin-relaxing protein system were measured in 2 mM MgCl2, 50mM KC1, and 10mM Tris-HC1 at pH 7.8 and 20 degrees in the presence and absence of 0.05-0.1 mM Ca2+ ions. The concentrations of H-meromyosin (HMM) and the F-actin-relaxing protein (F-A-PR) complex were 3.4 and 3 mg/ml, respectively, and the ATPase reaction was coupled with 4 mg/ml of pyruvate kinase [EC 2.7.1.40] and 1 or 20 mM phosphoenolpyruvate to regenerate ATP. The amount of ADP bound to HMM during the ATPase reaction was determined by measuring the amount of ADP remaining in the reaction mixture. The amount of ATP bound to HMM was determined by subtracting the amount of bound ADP from the total amount of nucleotides bound to HMM, which was measured by a rapid flow-dialysis method. The following results were obtained. 1. The ATPase activity of the HMM-F-A-RP system increased linearly with increase in the amount of ATP added, and was independent of the presence of 0.05 mM Ca2+, when the amount of ATP added was less than 1 mole/mole of HMM. In the presence of 0.05 mM Ca2+, the ATPase activity reached a maximal level when 1.2-1.5 mole of ATP was added per mole of HMM, and maintained this level even at 3 moles of added ATP/mole of HMM. In the presence of 3mM EGTA, the ATPase activity decreased with increase in the amount of ATP added, from 1.5 to 3 moles of ATP/mole of HMM, and reached the level of the HMM ATPase reaction at 3 moles of added ATP/mole of HMM. Similar results were observed when the concentration of HMM was maintained at 3.4 mg/ml and the concentration of the F-A-RP complex was decreased from 3 to 1 or 0.5 mg/ml.
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PMID:The amounts of adenosine di- and triphosphates bound to H-meromyosin and the adenosinetriphosphatase activity of the H-meromyosin-F-actin-relaxing protein system in the presence and absence of calcium ions. The physiological functions of the two routes of myosin adenosinetriphosphatase in muscle contraction. 12 89

In 2 mM MgATP, 0.08 ionic strength and 1 mM free Mg++ cardiac myofibrils bound 3.5 nmoles Ca/mg protein at maximal ATPase activation. Significant amounts of Ca were also bound to cardiac myosin with these same conditions. By subtraction of this myosin-bound Ca we obtained an estimate of 4 moles Ca bound per mole of myofibrillar troponin at maximal ATPase. We found, however, that Ca activation of myofibrillar ATPase could be estimated assuming that only two of troponin's Ca-binding sites are engaged in regulation of crossbridge activity. Increases in MgMTP from 0.3 to 5.0 mM raised the free Ca, giving half-maximal isomteric tension or ATPase. Although part of this shift is most probably due to changes in the number of rigor (nucleotide-free) actin-myosin linkages, the rightward shift of the free Ca++-activation relation with increase in MgATP from 2 to 5 mM appears to be due to effects of active (nucleotide-containing) actin-myosin linkages.
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PMID:Calcium regulation of cardiac myofibrillar activation: effects of MgATP. 12 91

Tightly bound adenine nucleotides are removed from multiple binding sites on beef heart mitochondrial ATPase (F1) by chromatography on columns of Sephadex equilibrated with 50% glycerol. Release of nucleotides from the enzyme is associated with large decreases in sedimentation velocity (from 11.9 S to 8.4 S) which may be observed in concentrated solutions of polyols. Polyol-induced conformational changes are reversed when the enzyme is returned to dilute buffers. The nucleotide-depleted enzyme restores oxidative phosphorylation in F1-deficient submitochondrial particles. Reconstitution of nucleotide-depleted F1 with the ATP analog (adenylyl-imidodiphosphate (AMP-PNP), almost 5 moles of AMP-PNP per mole of enzyme, results in preparations with substantially inhibited ATPase activity which nevertheless restores oxidative phosphorylation and the 32Pi-ATP exchange reaction in F1-deficient submitochondrial particles. Incubation of the analog-labeled enzyme with ATP and Mg++ results in partial displacement of the analog and a time-dependent recovery of ATPase activity.
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PMID:Physical and enzymatic properties of nucleotide-depleted beef heart mitochondrial adenosine triphosphatase. 12 61

A method is presented for obtaining the preparation of N+, K+-ATPase from the cattle brain. The specific activity of the preparation is 5 units (mu mole Pi per 1 min) per 1 mg of protein. A water-soluble derivate of carbodiimide is shown to inhibit reversibly both Na+, K+-ATPase and K+-phosphatase. ATP, Na+ and K+ manifest a protective effect against inhibition, and Na+ and K+ revealed a competition with the inhibitor for the enzyme. p-Chloromercuribenzoate inhibits irreversibly Na+, K+-ATPase and K+-phosphatase activities. The substrates ATP and p-nitrophenylphosphate protected these activities against inhibition. The phosphororganic compound O-n-butyl-S-(beta-ethyl-mercaptoethyl)-methyl thiophosphate has no significant effect on the Na+, K+-ATPase and K+-phosphatase activities.
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PMID:[Isolation of active preparation of Na+, K+-ATPase from cattle brain and study of the role of carboxyl, sulfhydryl and hydroxyl groups]. 12 66

Ouabain-binding and phosphorylation of (Na+ mk+)-ATPase (EC 3.6.1.3) of the plasma membranes from kidney were investigated after treatment with N-ethylmaleimide or oligomycin. Either of these inhibitors brought about the following changes: the phosphoenzyme, formed in the presence of Na+, Mg2+ and ATP became essentially insensitive to splitting by K+ but was split by ADP. One mole of this ADP-sensitive phosphoenzyme bound one mole of ouabain but the enzyme-ouabain complex was less stable than in the native enzyme primarily because the rate of its dissociation increased. Ouabain was bound to the ADP-sensitive phosphoenzyme in the presence of Mg2+ alone and addition of inorganic phosphate enhanced both the rate of formation and the steady-state level of the enzyme-ouabain complex. The inhibitors did not affect the properties of this second type of complex. Both in the native enzyme and in the enzyme treated with the two inhibitors inorganic phosphate enhanced ouabain binding by phosphorylating the active center of the enzyme as shown (a) by mapping the labeled peptides from the enzyme after peptic digestion, (b) by inhibition of this phosphorylation with Na+ and (c) by the 1:1 stoichiometric relation between this phosphorylation and the amount of bound ouabain. Unlike the phosphoenzyme, the binding of ouabain remained sensitive to K+ in the enzyme treated with the inhibitors. K+ slowed ouabain-binding either in the presence of Na+, Mg2+ and ATP or of Mg2+ and inorganic phosphate. A higher concentration of K+ was needed to slow ouabain-binding either in the presence of Na+, Mg2+ and ATP or of Mg2+ and inorganic phosphate. A higher concentration of K+ was needed to slow ouabain-binding than to stimulate dephosphorylation. This finding is interpreted as being an indication of separate sites for K+ on the enzyme: a site(s) with high K+-affinity which stimulates dephosphorylation, another site(s) with moderate K+-affinity which inhibits ouabain-binding. Inhibitors may enhance formation of the ADP-sensitive phosphoenzyme by blocking interaction between K+ and the site(s) with high affinity.
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PMID:Ouabain-binding and phosphorylation of (Na+ + K+) ATPase treated with N-ethylmaleimide or oligomycin. 12 64

Mild pulmonic stenosis was performed in dogs to evaluate the effect of systolic pressures overloading on the activity and subunits of myosin in the early hypertrophied right ventricle. Three weeks following pulmonary constriction, six hypertrophied dogs were sacrificed and compared to six sham-operated dogs which served as controls. In the right ventricular free wall of hypertrophied right ventricles (HRV), the heart/body weight was 46% greater than that of normal right ventricles (NRV) (p less than 0.01). Myosin ATPase activity (Vmax values) in mumoles phosphate/mg/min, was elevated significantly in the stressed ventricle for both K+ and Ca++ activity in hypertrophied right ventricles. Associated with the increase in myosin activity, there was an increase in proportion of heavy to light chains in myosin from HRV. There were approximately 2 moles of myosin light chains per mole of myosin heavy chains in NRV and approximately 1 mole of myosin light chains per mole of myosin heavy chains in HRV. The proportion of light chain C1 to C2, did not change in myosin from NRV and HRV. Of the C1 light chains, according to two-dimensional gel electrophoresis, there was less C1d as compared to C1c in HRV as compared to NRV. Thus K+- and Ca++- activated myosin is elevated in early canine HRV by pressure overload. It is suggested taht the augmented myosin activity is due to a reduction of light chain inhibition of myosin ATPase activity, which appears to result from the slower turnover rate of myosin light chains relative to heavy chains. Furthermore, when myosin light chains are added to hypertrophied right ventricular myosin, the ATPase activity is lowered.
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PMID:Modulation of myosin in right ventricular hypertrophy. 12 38

The subunit composition, the thiol group content and the biological activities of cardiac tropomyosins (TM) of various animal species were compared. Cardiac TM from small animals such as rabbit, guinea-pig, rat and dog contain 2 SH/mole and were resolved into one band on SDS and acid urea electrophoresis and into two bands on alkaline urea electrophoresis. Chicken cardiac TM likewise gave one band and it contains 4 SH/mole. In contrast pig, sheep and human cardiac TM contain respectively 2.6, 2.4, and 2.4 SH/mole and were resolved into two bands alpha and beta on the different electrophoresis systems used, with a beta:alpha ratio respectively of I:4.2, I:4.6, I:4.8. The alpha-TM components from sheep skeletal and pig and sheep cardiac muscles were more positively charged than the rabbit skeletal alpha-TM component, as shown in alkaline urea electrophoresis system. The alphaalpha and alphabeta combinations of dimers found for skeletal muscle by other authors, were also found for cardiac pig TM. All the TM have the same effect on the Ca2+-stimulated ATPase activity of desensitized actomyosin (DAM) and on the Mg2+-stimulated ATPase activity of DAM with troponin-complex. This work suggests that the subunits of the TM from skeletal and cardiac muscles are heterogenous in their M.W. and their charges and that in the heart as well as in skeletal muscle a relationship seems to exist between the amount of the beta component and the speed of contraction of the muscle: a higher amount of this component was found in the bulky hearts which are also those which contract slower.
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PMID:A comparative study of skeletal and cardiac tropomyosins: subunits, thiol group content and biological activities. 13 Dec 98

As previously reported, rho-nitrobenzenediazonium fluoroborate strongly inhibits Ca2+- ATPase of myosin [EC 3.6.1.3] without appreciable suppression of its EDTA-K+- ATPase activity, and the presence of ATP in the reaction medium reverses the pattern of alteration in both ATPase activities, i.e., causing selective inhibition of EDTA-K+ -ATPase. Spectrophotometric studies on the azo-coupling products of 17 amino acids and their derivatives revealed that the amino acid residue of myosin modified by the diazonium dye was cysteine in both the presence and absence of ATP. It is also suggested that the number of cysteinyl residues responsible for the activity changes was one mole per mole of myosin subunit.
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PMID:Thiols of myosin. III. Spectrophotometric identification of the amino acid residue of myosin modified by rho-nitrobenzenediazonium fluoroborate. 13 31

1. By changing the concentrations of Mg2+ and Ca2+ ions and ATP, the Ca2+, Mg2+-dependent ATPase [EC 3.6.1.3] of SR was converted to various enzymatic states, E, MgE, MgECa, MgEATP' CaECa, and CaECap at pH 8.0 and 0 degrees (cf. Eq. 1). 2. SR vesicles were allowed to react with 0.5 mM 2,4,6-trinitrobenzenesulfonate (TBS) at pH 8.0 and 0 degrees, keeping the ATPase in one of the enzymatic states listed above. Trinitrophenyl (TNP)-protein and TNP-lipid were separated by gel-filtration, and the amounts of TNP incorporated into protein and lipid were determined. 3. In all the enzymatic states of ATPase tested, the amount of TBS bound with SR protein increased exponentially with time, and reached a maximum level 10 min after starting the reaction. On the other hand, the amount of TBS bound to lipid increased with time, and did not reach a maximum level for at least 20 min. 4. The SR ATPase activity and the amount of EP formed decreased only slightly, even when the amount of TBS bound to SR protein reached the maximum level. 5. The maximum amount of TBS bound to SR protein varied on changing the enzymatic state of SR ATPase. Namely, about 2,3,1,3, or 4, and 3 moles of TNP were incorporated per mole of SR ATPase, when SR was allowed to react with TBS in the enzymatic states MgE, MgECa, MgEATP' CaECa, and CaECap, respectively. 6. When the enzymatic state was changed from MgE to MgECa 10 min after starting the reaction with TBS, about 4 moles of TBS was bound per mole of ATPase within 10 min, while the maximum levels of TBS bound in states MgE and MgECa were about 2 and 3 moles per mole of ATPase, respectively, as mentioned above. 7; When the enzymatic state was changed from MgE to MfEATP 10 min after starting the reaction with TBS, about 3 moles of TBS was bound per mole of ATPase within 10 min, while the maximum levels of TBS bound in states MgE and MgEATP were about 2 and 1 moles per mole of ATPase, respectively, as mentioned above. 8. When the enzymatic state was changed from CaECa to CaECap 10 min after starting the reaction with TBS, about 4 moles of TBS was bound per mole of ATPase, while the maximum levels of TBS bound in states CaECa and CaECap were about 3 or 4 moles per mole of ATPase, respectively. 9. A diagrammatic model of functional movements of the ATPase molecule coupled with elementary steps in the ATPase reaction is proposed on the basis of these results.
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PMID:Chemical modification of the Ca2+ -dependent ATPase of sarcoplasmic reticulum from skeletal muscle. II. Use of 2, 4, 6-trinitrobenzenesulfonate to show functional movements of the ATPase molecule. 13 37

The Mg-ATPase and (Na+ + K+)-stimulated Mg-ATPase in the mitochondrial and microsomal fraction of smooth muscular cells of the sheep's common carotid artery have been characterized in more detail. Optimal enzyme activities were found for all ATPases to be at pH 7.5-8.0 and 45 degrees C-50 degrees C. The energies of activation were found to be at 5-9 kcal/mole for both ATPases. Two-thirds of the (Na+ + K+)-stimulated Mg-ATPase were found to be ouabain-sensitive and thus attributed to the coupled (Na, K)-transport system. The pI 50 values of ouabain for microsomal and mitochondrial fractions are 6.3 and 6.0, respectively. The highest activity of (Na+ + K+)-stimulated Mg-ATPase is at 5-10 mM K+ and more than 50 mM Na+. One-third of the (Na+ + K+)-stimulated Mg-ATPase activity was found to be due to a stimulation of Mg-ATPase by Na+ alone, which is not inhibited by ouabain. The relationship of this activity to the ouabain-sensitive part of the (Na+ + K+)-stimulated Mg-ATPase and to Na+-transport is discussed. For the Mg-ATPases apparent KM(ATP) values were determined to be 1.4 and 1.0 mM, resp., and for the (Na+ + K+)-stimulated Mg-ATPases 0.15 and 0.14 mM, resp.
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PMID:Characterization of Mg-ATPase and (Na+ + K+)-stimulated Mg-ATPase in smooth muscular cells of the sheep's common carotid artery. 13 64


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