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PubMedDate not supplied

[Effect of beryllium salts on the activity of sarcoplasmic reticulum Ca2+,Mg2+-dependent ATP-ase].

In the presence of Mg2+ and Ca2+ ions beryllium compounds inhibit the Ca2+, Mg2+-dependent ATPase activity and the transport of Ca2+ in the sarcoplasmatic reticulum vesicles. The inhibition is reversible and concurrent with respect to the Mg2+ ions. In the absence of the Mg2+ ions an addition of beryllium compounds stimulates the ATPase activity, the dependence of the degree of its stimulation on the beryllium compounds concentration is characterized by a curve with a maximum. On the membranous Ca2+, Mg2+-dependent ATPase preparations beryllium compounds produce a stronger inhibiting effect than in the case of the purified enzyme, which is, apparently, due to their ability to influence the membranous structure. The hydrophobic spin probe method shows that beryllium compounds reduce the microviscosity of the lipid sections of the membrane.

Animals↗
PubMed1979

Optical probe responses on sarcoplasmic reticulum. Oxacarbocyanines.

Absorbance and fluorescence changes of oxacarbocyanine dyes during ATP-induced Ca2+ transport in rabbit sarcoplasmic reticulum were analyzed. The response of the probes is complex and contains contributions from the binding of Ca2+ and ATP to the membrane. In a medium of 0.12 M KCl and 5 mM MgCl2, the fluorescence of Di-O-C5(3) is decreased by Ca2+ or ATP with apparent dissociation constants of 0.2 and 5 micron, respectively. This suggests that oxacarbocyanines respond to binding of Ca2+ and ATP at the active site of Ca2+ transport ATPase. The effect of ATP is observed in the absence of divalent cations. Further changes in the fluorescence or absorbance of cyanine dyes occur at millimolar concentrations of Ca2+ or during ATP-induced Ca2+ uptake, which can be related to Ca2+ binding to low affinity, relatively nonspecific binding sites on the membrane, that can also bind K+ and Mg2+. The optical changes due to Ca2+ accumulation are most pronounced in media of 0.25 M sucrose and much reduced in 0.12 M KCl and 5 mM MgCl2, in accord with competition by K+ and Mg2+ for the low affinity Ca2+ binding sites. These effects must be taken into account in the evaluation of the magnitude and direction of membrane potential in sarcoplasmic reticulum vesicles during Ca2+ uptake and release.

Adenosine Triphosphate↗
PubMedDate not supplied

[Effect of thyroid hormones on the calcium pump in sarcoplasmic reticulum].

In vitro thyroxine inhibited accumulation of Ca2+ by fragments of sarcoplasmic reticulum, isolated from rabbit sceletal muscles. The inhibitory effect of thyroxine was responsible for its direct action on Ca2+ dependent ATPase. Half-maximal inhibition of the enzymatic activity occurred at the same concentrations of thyroxine using both membrane-bound and highly purified solubilized forms of Ca2+-ATPase (15--20 micrometer and 10 micrometer of the hormone, respectively). Triiodothyronine was similar in the effect but not diiodothyrosine, which did not possess the hormonal activity. The data obtained suggest that thyroid hormones affect the mechanism of dephosphorylation in ATP-hydrolase reaction.

Animals↗
PubMed1979

[Investigation of sarcoplasmic reticulum SH-groups].

The amount and the reaction capacity of the thiol groups in the sarcoplasmic reticulum containing up to 86% of Ca-ATPase were determined using 7-chloro-4-nitrobenzo-2-hydroxo-1,3-diazole (NBD-chloride). The total amount of SH-groups interacting with NBD-chloride is about 9 moles/10(5) g of protein as determined in the excess of NBD-chloride (750 micrometers). With respect to their sensitivity to NBD-chloride the SH-groups may be divided into two classes: slow and fast ones (5,3 and 3,5 moles/10(5) g of protein, respectively). The modification constants for the fast and slow SH-groups are 0,16 and 0,015min-1. ATP (30 micrometers) decreases the number of fast groups by 1 mole/10(5) g of protein. At higher concentrations of ATP (1--3 mM) the amount of fast SH-groups is decreased by 3 moles/10(5) g of protein, their modification rate constant being decreased 2-fold. ATP at concentration of 1 mM, decreases the rate constant for the Ca-ATPase inactivation by NBD-chloride from 0.68 down to 0,073 min-1, which coincides with the modification rate constant for fast SH-groups (0,071 min-1) under the same conditions. Ca2+ at concentration of 10(-4) M increases the amount of fast thiol groups by 1 mole/10(5) g of protein, the rate constant of their modification by NBD-chloride being increased 2-fold. A half-maximal effect was observed in the presence of 5.10(-7) M Ca2+ . Mg2+ did not affect the total amount of fast thiol groups; however, it decreased their modification rate constant.

4-Chloro-7-nitrobenzofurazan↗
PubMed1979

On the mechanism of Ca2+-dependent adenosine triphosphatase of sarcoplasmic reticulum. Occurrence of two types of phosphoenzyme intermediates in the presence of KCl.

The steady state kinetics of ATP hydrolysis by partially purified adenosine triphosphatase preparations of sarcoplasmic reticulum was investigated at 0 degrees C and pH 7.0 in 2.0 mM MgCl2, 20 microM [gamma-32P]ATP, 20 microM CaCl2, and various concentrations of KCl in the presence and absence of 12% dimethyl sulfoxide. The steady state phosphoenzyme formed under these conditions could be resolved kinetically into ADP-sensitive and ADP-insensitive forms. These steady state kinetic data were analyzed according to a scheme in which the ADP-sensitive and ADP-insensitive phosphoenzymes occur sequentially, and Pi is derived from the latter. The KCl-dependent turnover rate of the ADP-insensitive phosphoenzyme that was estimated according to this scheme was in good agreement with the directly measured hydrolysis rate constant of the ADP-insensitive phosphoenzyme. In addition, the time course of the decomposition of the total amount of phosphoenzyme, measured after a steady state level was reached in 20 mM KCl and further phosphorylation was prevented by addition of excess ethylene glycol bis(beta-aminoethyl ether)N,N,N',N'-tetraacetic acid, was also in agreement with that calculated according to this scheme using values of the rate constants estimated from the amounts of the ADP-sensitive and ADP-insensitive phosphoenzymes and the rate of ATP hydrolysis. These results, together with our previous findings, support the view that this scheme describes the mechanism of ATP hydrolysis in the presence of KCl.

Adenosine Triphosphate↗
PubMedDate not supplied

[Molecular organization of Mg2+, Ca2+-ATPase of sarcoplasmic reticulum].

The article deals with the results of studies on the structure and properties of discrete sites in a molecule of sarcoplasmic reticulum Mg2+, Ca2+-ATPase obtained during its fragmentation in the process of its limited hydrolysis by trypsin. It is established to contain three fragments with the molecular mass of 45 000, 30 000 and 20 000 Daltons. Some properties of these fragments are determined by the amino acid analysis, inhibitory analysis with application of radiactive labels and also of immunochemical analysis. The properties show that the first fragment is hydrophobic and the others are hydrophilic; these properties show that the first fragment is hydrophobic and the others are hydrophilic; these properties determine the location of the fragments in the sarcoplasmic reticulum membrane. The fragment with the molecular mass of 45 000 Daltons forms in it a nonspecific channel as if "sewing" it, two other fragments of the Mg2+, Ca2+-ATPase are located at the outer side of the membrane, the fragment with the molecular weight of 20 000 occupying a middle position between the fragments with molecular weight of 45 000 and 30 000, thus creating a selective respect to calcium "valve" to the nonspecific channel. This discrete part of Mg2+, Ca2+-ATPase possesses the ionophoric activity. The fragment with molecular weight of 30 000 is the energy converter. The site hydrolyzing AMP is located in it. The models (hypothetic) are presented for the Ca2+ active transpprt through biological membranes with Mg2+, Ca2+-ATPase participation.

Animals↗
PubMedDate not supplied

[Transmembrane potential formation upon ATP hydrolysis in sarcoplasmic reticulum].

Fluorescent cyanine (diS-C3-(5), diS-C2-(5), diO-C3-(5)) and oxonol (diBA-C4-(5)) potential-dependent dyes appeared to be extremely effective in detecting and studying the potential formed on the fragmented sarcoplasmic reticulum membrane under Ca2+ transport When [Ca2+] less than 5 X 10(-7) M ATP hydrolysis leads to formation of transmembrane potential (positive inside vesicules) caused by the Ca-independent ATPase activity. The potential is formed by a monovalent ion, presumably by H+, and possibly by Mg2+ ions. Ca-dependent ATPase activation by Ca2+ makes the potential to drop sharply and successive Ca2+ transport proceeds at low potential value. When Ca2+ has been accumulated by vesicules the Ca-independent ATPase restores positive potential. The potentials generated by both Ca-independent (10--30 mv) and Ca-dependent (-20 divided by -40 mv) ATPases have been estimated on the basis of the Nernst's equation with the help of positive and negative diffusion potentials formed by MgCl2 and CaCl2 gradients. The Ca2+ transport is shown not to be due to transmembrane electrophoresis but Ca-dependent ATPase action. The results suggest quite clearly that Ca-dependent ATPase operates as electrogenic Ca2+/H+, Mg2+-exchanger. The functional role of Ca-independent ATPase is, possibly, in compensation of charge effects when Ca2+ ions are passing through the membranes. The model illustrating the electrogenicity of Ca-independent and Ca-dependent ATPases action during Ca2+ transport in SR membranes has been proposed.

Adenosine Triphosphate↗
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

[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↗