Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.6.1.3 (ATPase)
 65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The calcium-dependent regulatory proteins, calmodulins, have been isolated from human blood platelets and guinea pig peritoneal polymorphonuclear leucocytes using the urea methanol procedure of Grand et al. [Biochem. J. 177, 521-529 (1978)]. The calmodulins were purified to homogeneity as indicated by polyacrylamide gel electrophoresis and both proteins comigrated with bovine brain calmodulin with mobilities corresponding to molecular weights of 16 000-17 000. The yield of calmodulin from platelets was higher on a wet weight basis than the yield from leucocytes but the former compared favourably with yields reported for brain and other tissues. Both calmodulin preparations significantly stimulated brain cyclic nucleotide phosphodiesterase, erythrocyte ghost Ca2+ ATPase and platelet phosphorylase kinase activities at the microgram level. Stimulation of Lubrol-solubilised brain adenylate cyclase was only marginally significant with platelet calmodulin and rarely demonstrable with the leucocyte preparations. Although biological activities of both proteins were retained during storage at -20 degrees C, higher-molecular-weight aggregates slowly formed which could not be dissociated during dodecylsulphate/mercaptoethanol denaturation.
 ...
PMID:Platelet and leucocyte calmodulins: isolation and characterisation. 627 36

Sarcolemmal vesicles were prepared from bovine cardiac muscle by differential and discontinuous sucrose density gradient centrifugation. Na+/K+-ATPase was purified 33-fold to a specific activity of 53 +/- 0.5 (12) mumol Pi X mg-1 X h-1, binding sites for strophantin 20-fold to a density of 56.3 +/- 5.3 (14) pmol/mg and that for the calcium antagonist nitrendipine 5.5-fold to a density of 0.72 +/- 0.07 (6) pmol/mg. The specific activity of the Na+/Ca2+ exchanger was 61.1 +/- 3.7 (6) nmol/mg. The vesicles had an intravesicular volume of 20 +/- 4 (4) microliter/mg and 56.9 +/- 6 (4)% of the vesicles were right-side-out oriented. Several peptides of the purified membranes were phosphorylated in the presence of Mg . ATP and EGTA. Most of the radioactive phosphate was incorporated into a peptide with an apparent molecular mass of 22 kDa. Denaturation of the membranes at 100 degrees C changed the mobility of this peptide to 15 kDa and 11 kDa. This peptide could not be distinguished from a sarcoplasmic reticulum peptide of similar molecular mass. The phosphorylation of the sarcolemmal peptide was stimulated by Ca2+/calmodulin, cAMP and the catalytic subunit of cAMP-dependent protein kinase. A comparison of the phosphorylation of sarcolemmal membranes with that of sarcoplasmic reticulum showed that Ca2+/calmodulin stimulated in each membrane, the phosphorylation of the 22-kDa peptide and a 44-kDa peptide, and in the sarcoplasmic reticulum the phosphorylation of an additional peptide of 55-kDa. Ca2+/calmodulin-dependent phosphorylation of a 55-kDa peptide could not be demonstrated in sarcolemma, regardless if sarcolemmal membranes were incubated together with sarcoplasmic reticulum or if the phosphorylation was carried out in the presence of purified cardiac myosin light chain kinase or phosphorylase kinase. 'Depolarization' induced Ca2+ uptake which was measured according to Bartschat, D.K., Cyr, D.L. and Lindenmayer, G.E. [(1980) J. Biol. Chem. 255, 10044-10047] was 5 nmol/mg protein. This uptake was not enhanced after preincubation of the vesicles with Mg . ATP or Mg . ATP and cAMP-dependent protein kinase. The value of 5 nmol/mg protein is in agreement with the theoretical amount of Ca2+ which can be accumulated by the bovine cardiac sarcolemma in the absence of a driving force other than the Ca2+ gradient. The potassium-stimulated Ca2+ uptake was not blocked by the organic Ca2+ channel blockers. Prolonged incubation of Mg . ATP with sarcolemmal vesicles in the presence of various ATPase inhibitors led to the hydrolysis of ATP. The liberated phosphate precipitated with Ca2+ in the presence of LaCl3. These precipitates amounted to an apparent Ca2+ uptake ranging from 50 to over 1000 nmol/mg. The results suggest that potassium-stimulated Ca2+ uptake of bovine cardiac sarcolemmal vesicles is not enhanced in the presence of ATP or by phosphorylation of a 22-kDa peptide.
 ...
PMID:Phosphorylation of purified bovine cardiac sarcolemma and potassium-stimulated calcium uptake. 630 17

khe conformational and functional events in calmodulin (CaM) are disproportionate to the mean saturation by Ca2+. The enhancement of intrinsic tyrosine fluorescence closely follows the appearance of species CaM X Can greater than or equal to 1; the exposure of the hydrophobic patch at the surface of CaM coincides with the appearance of CaM X Can greater than or equal to 2. For the activation of four different target enzymes, i.e., brain phosphodiesterase and adenylate cyclase, red blood cell Ca,Mg-ATPase, and skeletal muscle phosphorylase b kinase, CaM X Can greater than or equal to 3 is required. The different enzymes have the same affinity for the active species. The direct interaction of CaM with Ca2+ and phosphorylase b kinase has been analyzed according to the theory of energy coupling: whereas the first two stoichiometric calcium-binding constants in the complex are not significantly different from those of free CaM, the third Ca2+ binds with an affinity at least 10(6)-fold higher to enzyme-bound CaM than to free CaM, which corresponds to a free energy coupling of -7 kcal/mol CaM. The similarities in the activation mechanism of different enzymes suggest the existence of one unique CaM-binding domain. The characteristics of the interaction between CaM and melittin, a small amphiphatic cytotoxin, led us to propose melittin as a model for such a CaM-binding domain.
 ...
PMID:Sequential events in calmodulin on binding with calcium and interaction with target enzymes. 650 74

The effects of both high voltage and low voltage electrical stimulation were studied in rabbit Longissimus dorsi muscles. The rate of fall of pH as well as the activities of phosphorylase a, phosphorylase kinase, and phosphorylase phosphatase were measured. The effects on the yield, ATPase activities, and calcium permeability of the sarcoplasmic reticulum (SR) were also measured. Although only high voltage stimulation increased the post-stimulation rate of pH fall, both types of electrical stimulation increased the phosphorylase a activity, apparently by increasing the activity of phosphorylase kinase and destroying a large part of the phosphorylase phosphatase activity. Electrical stimulation reduced the yield of SR and increased its basal ATPase activity. It also increased the ability of the SR to retain accumulated calcium. We conclude that the different rates of pH fall observed following the two types of stimulation are due to the differential effects of these treatments on one of the ATPase activities, probably the myofibrillar ATPase.
 ...
PMID:Post-mortem glycolysis in rabbit Longissimus dorsi muscles following electrical stimulation. 2205 99


<< Previous 1 2