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At least 217 records · Page 12Linked to original sources
PubMed1979

Human erythrocyte calmodulin. Further chemical characterization and the site of its interaction with the membrane.

Human erythrocyte and bovine brain calmodulins were indistinguishable by tryptic peptide mapping, indicating that the primary sequence of the two proteins is either very similar or identical. Calcium binding determinations of human erythrocyte calmodulin, by equilibrium dialysis and fluorescence titration, were in close agreement with previous studies on other calmodulins. The calcium-activated adenosine triphosphatase which is stimulated by calmodulin was shown to be firmly associated with smooth erythrocyte plasma membranes devoid of spectrin and actin. Kinetic titration demonstrated that there are 4500 calmodulin binding sites per erythrocyte and that the turnover number of this calcium-activated adenosine triphosphatase is 3000 mumol of Pi . (mumol of site)-1 . min-1 which is similar to the turnover numbers of other transport adenosine triphosphatases. Furthermore, calmodulin stimulates calcium-activated adenosine triphosphatase by a simple enzyme-ligand association.

Animals↗
PubMedDate not supplied

[Temperature-dependent functional changes in sarcoplasmic reticulum membranes].

Temperature effect on changes in calcium ion transport and activity of Ca-ATPase of sarcoplasmic reticulum vesicles (SRV) was studied. Several temperature intervals of the change of SRV functional activity parameters were found: 8-12 degrees C-beginning of accumulation of SRV Ca2+, 12-19 degrees sharp activation of Ca2+ accumulation, 27-32 degrees-activation of passive yield, 36-43 degrees-reversible change of the activity of the accumulation system and activation of Ca yield, 48 degrees and higher--irreversible denaturation of transport Ca-ATPase. Coincidence of temperature intervals of SRV structural reconstructions, detected by means of fluorescent probes and functional changes points to a close relationship between structural reconstructions and functional responses of biological membranes.

Animals↗
PubMed1979

Calcium uptake by sarcoplasmic reticulum of rat muscle: inhibition by DDT.

Sarcoplasmic reticulum fragments capable of accumulating calcium were isolated from rat skeletal muscle by differential and sucrose gradient centrifugation. The ability of these fragments to accumulate calcium was impaired by adding 2,2-bis-(p-chlorophenyl)-1,1,1-trichloroethane (DDT) to the assay medium at concentrations of 0.06 to 6 muM. DDT (6 muM) caused a sharp lag in calcium uptake, with an 82% reduction in reaction rate 30 sec after calcium was added and a 62% reduction after one min. Basal ATPase activity of the microsomal fraction was inhibited by DDT but the calcium-stimulated increment of ATP hydrolysis was not. The findings show that DDT hinders calcium uptake by sarcoplasmic reticulum, but by some means other than inhibition of the calcium-stimulated ATPase. An apparent antagonism between DDT and ouabain or oligomycin was indicated. We propose that the presence of the lipid-soluble DDT molecule within the membrane of the sarcoplasmic reticulum interferes with the normal rapid uptake of calcium ions required for muscle relaxation, and that this interference may contribute to loss of muscle control in organisms poisoned by DDT.

Animals↗
PubMed1979

Substrate regulation of the sarcoplasmic reticulum ATPase. Transient kinetic studies.

The rate of phosphorylation of the Ca2+-dependent ATPase of sarcoplasmic reticulum vesicles by ITP and ATP was studied using a millisecond mixing and quenching device. The rate of phosphorylation was slower when the vesicles were preincubated in a Ca2+-free medium than when preincubated with Ca2+, regardless of the substrate used and of the pH of the medium. When the vesicles were preincubated with Ca2+ at pH 7.4 an overshoot of phosphorylation was observed in the presence of ITP. The overshoot was abolished when the pH of the medium was decreased to 6.0 or when the vesicles were preincubated in a Ca2+-free medium. Using vesicles preincubated with Ca2+ the apparent Km for ITP found was 2.5 mM at pH 6.0 and 1.0 mM at pH 7.4. The Vmax observed (77 mumol g-1 s-1) did not change with the pH of the medium. Both at pH 6.0 and 7.4 the apparent Km for ATP was 3 microM when preincubated in a Ca2+-free medium. At pH 6.0 the Vmax for ATP varied from 96 to 33 mumol g-1 s-1 depending on whether the vesicles were preincubated in the presence or absence of Ca2+. At pH 7.4 the Vmax for ATP was 90 mumol g-1 s-1 in both conditions. The rate of phosphorylation of the vesicles was dependent on the relative Ca2+ and Mg2+ concentrations of the reaction medium regardless of the substrate used.

Adenosine Triphosphate↗
PubMed1979

Diamide inhibited (Ca++ + Mg++) and (Mg++) dependent ATPase in erythrocyte membranes: activity at different temperatures.

After inhibition of the monovalent cation dependent ATPase, a (Ca++ + Mg++) and a (Mg++) dependent ATPase activity can be detected. The inhibition due to diamide on the (Mg++) ATPase, assayed in the 12.5 degrees C - 30 degrees C temperature range, is almost complete. On the contrary the diamide induced inhibition of (Ca++ + Mg++) ATPase, in the same temperature range, is not complete and the residual activity increases with temperature. The reported data indicate that the ATPase activity induced by calcium is much less diamide-sensitive and -SH-dependent than that elicited by Mg++ alone.

Adenosine Triphosphatases↗
PubMed1979

[Effect of thermostable protein kinase modulator on Mg, Ca-ATPase from nervous tissue].

Isoelectric focusing of a purified fraction of thermostable modulator of 3',5'-AMP-dependent protein kinase revealed five individual proteins, the main protein having an isoelectric point of 4,05. The molecular weight of this protein as determined by gel filtration is 8000--9000. The protein with a pI of 4,05 binds Ca2+ and in contrast to the original modulator inhibits the endogenous 3',5'-AMP-dependent phosphorylation of synaptic membranes. An addition of the original modulator fraction to the microsomes isolated from nervous tissue increases the Mg, Ca-ATPase activity and absorption of 45Ca. Neither the protein with a pI of 4,05 nor other individual proteins affect the activity of transport ATPase. The activating effect is partly restored after mixing of all the five subfractions. It is assumed that these proteins are aggregated by Ca2+ and change the activity of ATPase or membrane 3',5'-AMP-dependent protein kinase depending on the concentration of calcium ions.

Animals↗
PubMedDate not supplied

[Participation of Mg2+ and Ca2+ ions and the corresponding ATPases in the mechanism of the presynaptic action of amisyl and arecoline].

Amisyle and arecoline were found to be antagonistic drugs in the effect on content of Mg2+ and Ca2+ and on activity of corresponding ATPases in synaptosomes isolated from rat brain. Amisyle promoted the incorporation of 45Ca into synaptosomes but arecoline inhibited the reaction. The appear to be responsible for liberation and maintaining of neurotransmitters in presinaptic stores.

Adenosine Triphosphatases↗
PubMed1979

Subcellular calcium localization and AT0-dependent Ca2+-uptake by smooth endoplasmic reticulum in an invertebrate photoreceptor cell. An ultrastrucutral, cytochemical and X-ray microanalytical study.

In Hirudo medicinalis an extensive and highly elaborate three dimensional network of smooth endoplasmic reticulum cisternae is found in very close structural relationship to the receptive (microvillar) membrane, as reported for many other invertebrates. A variant of the potassium pyroantimonate technique showed that these submicrovillar endoplasmic reticulum cisternae (SMC) and mitochondria are major intracellular calcium stores. Furthermore, using saponine-skinned photoreceptors for an in situ accumulation experiment, calcium oxalate precipitates in SMC demonstrate that this organelle is able to accumulate Ca2+ from a concentration of 2 x 10(-5) M, when ATP, Mg2+, and oxalate ions are present in the accumulation medium. This result provides direct evidence for the hypothesis that SMC may play a particularly important role in the regulation of intracellular ionized calcium in invertebrate photoreceptor cells. Morphological evidence supports this view.

Animals↗
PubMed1979

[Biochemical mechanisms for the effect of alcohol on the brain].

This paper reviews and discusses basic knowledge of biochemical mechanisms of action of ethanol upon the central nervous system, the emphasis being on effects upon cerebral membrane structures and processes as well as mechanisms of chemical synaptic transmission. Results of detailed studies into material and steric changes in membranes, ion-dependent adenosine triphosphatases, variations in ion balance, effects upon cyclic nucleotides, influences on special transmitter systems, and mechanisms of formation of morphine-analogous condensation products are presented. In addition, open questions are derived and formulated in problem complexes.

Acetaldehyde↗
PubMed1979

[Studies of the presence of enzymes in various tissues of swine. 5. Studies of the activity and properties of adenosine triphosphatases in the pancreas].

Studies were conducted into the activities of magnesium-ATPase, sodium-potassium-ATPase, and HCO3-ATPase in homogenates of pancreas of 19 foetuses, with body weights between 340 g and 1,642 g, two piglets, with body weights of 9 kg and 10 kg, and four adult pigs. While general enzyme activity was low during foetal development, highest activies usually were recordable from HCO3-ATPase. High activities were recorded from both the piglets and adult pigs. The highest data, again, were recordable from HCO3-ATPase which is essential to the secretion of HCO3 ions. Maximum activity of magnesium-ATPase was based on an ATP-magnesium ratio of 1:1. HCO3-ATPase was best activated by 25 mM NaHCO3 and exhibited high stability to temperature. The activities of magnesium-ATPase and of HCO3-ATPase were inhibited by 10 mM of Rhodanid. Calcium-ATPase reached its maximum activity in response to 5 mM calcium concentration.

Adenosine Triphosphatases↗
PubMed1979

[Role of calcium in realization of nervous control during RNA synthesis in skeletal muscles].

The effects of Ca2+ on the RNA polymerase activity of the nuclei isolated from normal and denervated gastrocnemius muscles of the rabbit were studied. It was shown that 18 hrs after denervation the RNA synthesis in vitro, Ca2+ content and the Ca, Mg-ATPase activity of the nuclei are decreased. After addition of exogenous Ca2+ the incorporation of labelled UTP into the nuclei is stimulated in the denervated muscle and is inhibited in the control. Electrostimulation of the denervated muscle at the peripheral part of the sciatic nerve for 3 hrs increases both the RNA synthesis in the nuclei and the Ca2+ content, as well as the Ca, Mg-ATPase activity. Exogenous Ca2+ has an inhibitory effect on the nuclei of the stimulated muscle. The correlation established is indicative of participation of Ca2+ in the transmission of excitation in skeletal muscle sarcolemma to the processes occurring in nuclear structures.

Animals↗
PubMedDate not supplied

[The effect of catecholamines on the Ca2(+)-adenosinetriphosphatase of the sarcoplasmic reticulum in the skeletal muscles in chicken ontogeny].

It has been shown that the activity of Ca(2+)-ATPase increases during development. Epinephrine in vivo increases the activity of Ca(2+)-ATPase in chick skeletal muscles. The effect of hormone is lacking at embryonic stages of development and appears only before hatching. In the presence of exogenous protein kinase, cAMP also increases the activity of the enzyme, this effect being observed also in embryonic muscles. Lack of effect of epinephrine on Ca(2+)-ATPase in embryonic muscles is associated with non-reactivity of their adenylate cyclase to catecholamines. Ca(2+)-ATPase itself already at embryonic period is ready to react to cAMP. It is concluded that Ca(2+)-ATPase of sarcoplasmic reticulum is one of the sites of action of catecholamines on calcium metabolism in muscle cell and that this action is realized via the system adenylate cyclase-cAMP-protein kinase.

Animals↗