Exposure of the purified Ca2+ pump of human erythrocytes to chymotrypsin led to the rapid loss of calmodulin activation. A fragment of about 12 kDa was removed from the ATPase in 1-2 min. Blotting experiments with 125I-labeled calmodulin showed that this fragment contains the calmodulin binding region.
View Article and Find Full Text PDFBiochem Biophys Res Commun
February 1988
Calmodulin increases about three-fold in rat liver nuclei after partial hepatectomy. The increase is maximal after 24 hours, when DNA synthesis is also maximal. During the same time re-distribution of calmodulin within the nuclear structure takes place, leading to its association with the nuclear matrix.
View Article and Find Full Text PDFIt has been proposed that the plasma membrane Ca2+ pump of smooth muscle tissues may be regulated by cGMP-dependent phosphorylation [Popescu, L. M., Panoiu, C.
View Article and Find Full Text PDFIt was recently shown that the mitochondrial isozyme of heart creatine kinase binds to cardiolipin on the outer half of the inner membrane [Müller, M., et al. (1985) J.
View Article and Find Full Text PDFAdv Second Messenger Phosphoprotein Res
October 1988
J Cardiovasc Pharmacol
May 1989
Calcium is a signaling element of general importance to cells. In muscle, its key function is the activation of troponin C, which is essential for the contraction of myofibrils in skeletal and heart muscles, and of myosin light chain kinase, which is essential for the contraction of smooth muscles. Calcium modulates the latter enzyme through the calcium-binding protein calmodulin, which may also control other calcium-binding proteins involved in the contraction of smooth muscles.
View Article and Find Full Text PDFChemically modified calmodulins have been used to investigate structural features which are important for the interaction of the activator with targets. Carbamoylation of lysine residues had no influence on the ability of calmodulin to stimulate the plasma membrane Ca2+-ATPase whereas the stimulation of the bovine brain cyclic-nucleotide phosphodiesterase was reduced up to 50%. Different species of carbamoylated calmodulin have been isolated but no differences were detected in their interaction with the cyclic-nucleotide phosphodiesterase.
View Article and Find Full Text PDFBiochem Biophys Res Commun
November 1987
The amino acid sequence of a peptide isolated from a CNBr digest of the erythrocyte Ca2+ ATPase has been determined. It contains a highly conserved phosphorylation site sequence common to all aspartyl-phosphate forming ion motive ATPases which have been sequenced so far.
View Article and Find Full Text PDFThe benzothiazepine diltiazem is a potent Ca-channel blocker, which also inhibits the Na-dependent Ca-efflux from heart mitochondria. In this study, the action of the 4 stereoisomers of diltiazem has been investigated using guinea-pig heart and liver mitochondria. The rate of the Na-dependent Ca-efflux from liver mitochondria has been found to be 10 times smaller than in heart mitochondria.
View Article and Find Full Text PDFThree nuclear subfractions were prepared from isolated hepatocytes nuclei. The calmodulin content in whole nuclei was 79 ng/mg of protein. The soluble fraction obtained after digestion of the nuclei with DNase I and RNase A (S1 fraction) contained 252 ng of calmodulin/mg of protein.
View Article and Find Full Text PDFBiochem Biophys Res Commun
June 1987
The Na+/Ca2+ exchanger of calf heart sarcolemma has been identified in solubilized membrane preparations with the help of specific antibodies as a molecule of approximate Mr of 30 KDa. The conclusion supports the previous proposal by Soldati et al. (J.
View Article and Find Full Text PDFDifferent conformational states of the purified plasma membrane Ca2+-ATPase from pig erythrocytes have been detected by circular dichroism (CD) and fluorescence spectroscopy. The helical content of the enzyme decreased by about 10% in the transition from the Ca2+ high-affinity form (10 microM free Ca2+ = E1 state) to the VO4(3-)-inhibited state (20 microM VO4(3-) = E2 state). The changes in the CD spectra did not show full reversibility upon reversing the E1-E2 transition, whereas those in the fluorescence spectra did.
View Article and Find Full Text PDFThe kinetics of active Ca2+ transport in inside-out red cell membrane vesicles and the Ca2+-ATPase activity of the purified Ca2+ pump were studied and the effects of calmodulin, acidic phospholipids, and controlled trypsinization were compared. In the presence of calmodulin the maximal rate and the apparent affinity of the pump for Ca2+ were greatly increased in both preparations. The lowest value of Km(Ca) was between 0.
View Article and Find Full Text PDFVarious Ca2+-antagonists and related compounds were probed for possible anti-calmodulin properties. Some of them efficiently inhibit calmodulin dependent activity (the plasma membrane Ca2+-ATPase and the cyclic nucleotide phosphodiesterase). The I50-values for the most potent inhibitors varied between 15 and 30 uM.
View Article and Find Full Text PDFSoc Gen Physiol Ser
February 1989
Eukaryotic plasma membranes contain three Ca-transporting systems: a Ca channel, an ATPase, and an Na/Ca exchanger. The ATPase is high-affinity, low-capacity system, which continuously pumps Ca out of cells. The Na/Ca exchanger is a low-affinity, high-capacity system, which is particularly active in excitable cells.
View Article and Find Full Text PDFPhospholamban (PLB) from cardiac sarcoplasmic reticulum (SR) was phosphorylated under various conditions by the adenosine cyclic 3',5'-phosphate (cAMP)-dependent and/or the calmodulin-dependent protein kinase. The small shifts in apparent molecular weight resulting from the incorporation of Pi groups in the PLB complexes were analyzed by high-resolution sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In parallel experiments, PLB was dissociated into its subunits and analyzed by using a newly developed isoelectric focusing system.
View Article and Find Full Text PDFThe purified Ca2+ ATPase of the erythrocyte plasma membrane has been submitted to controlled trypsin proteolysis under conditions that favor either its (putative) E1 or E2 configurations. The former configuration has been forced by treating the enzyme with Ca2+-saturated calmodulin, the latter with vanadate and Mg2+. The E1 conformation leads to the accumulation of a polypeptide of Mr 85 KDa which still binds calmodulin, the E2 conformation to the accumulation of one of Mr 81 KDa which does not.
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