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Results for “Calcium-Transporting ATPases”

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PubMed1990

Stimulation of rat red blood cell glycolysis by phenylhydrazine hydrochloride.

The effects of phenylhydrazine hydrochloride (5, 10 and 20 mM) on the energy metabolism of red cells of rats were studied. There were found an 1.3-2-fold increase of lactate formation, an up to seven-fold accumulation of pyruvate and of the flux via the oxidative pentose pathway. The stimulation of the glycolysis was caused by 1) a large decline of the ATP concentration and a corresponding increase of ADP and AMP, and 2) by the stimulation of the actual activities of the Na+,K(+)-ATPase and Ca+(+)-ATPase owing to a greater permeability of the plasma membrane. A significant increase of the Ca+(+)-influx was demonstrated. A decline of the sum of adenine nucleotides after 60 and 90 min of incubation with phenylhydrazine was not accompanied by accumulation of hypoxanthine.

Adenine Nucleotides↗
PubMed1990

Monomeric state and Ca2+ transport by sarcoplasmic reticulum Ca2(+)-ATPase, reconstituted with an excess of phospholipid.

The structural basis for Ca2+ transport was examined in vesicles reconstituted with an excess of phospholipid by a cholate dialysis procedure. Unincorporated protein and vesicles with a relatively high protein content were removed by sucrose density centrifugation (3-12%), leaving a fraction of lipid-rich vesicles (lipid to protein weight ratio 800-900:1) with a high coupling ratio (1.0) and transport capacity (25 mumol/mg protein, after Ca-phosphate loading). Freeze-fracture analysis showed that the reconstituted vesicles had a remarkably narrow size distribution (diameter 794 +/- 77 A (S.D.], suitable for stereological analysis. Intramembranous particles were dispersed and occurred with a low frequency in the fractured shells, also before sucrose fractionation. It was calculated that the number of intramembranous particles corresponded to the number of Ca2(+)-ATPase polypeptide/vesicle. A ratio of unity between particles and polypeptide chains was also obtained from the density of particle distribution on flat surfaces of fused vesicles, prepared by sucrose fractionation. The size of the particles formed a broad distribution, having a peak value around 60-67 A, both in the reconstituted preparation and sarcoplasmic reticulum vesicles. No evidence for protein-protein interactions was found in chemical cross-linking experiments. It is concluded that the intramembranous particles in the reconstituted preparations are referable to monomeric Ca2(+)-ATPase which is capable of transporting Ca2+ inside the vesicles. The implications of the observations for the associational state of Ca2(+)-ATPase at high protein concentration are considered in relation to previous ultrastructural investigations of membranous Ca2(+)-ATPase in native and two-dimensional-crystalline forms.

Animals↗
PubMed1990

[A theoretical study on the regulation mechanism of Ca2+ concentration in lens related to the Ca2+ dependence of Ca2(+)-ATPase activity].

A four-state model for the elementary process of the Ca2+ active transport system in lens was proposed, and based upon this model the Ca2+ dependence of Ca2(+)-ATPase activity was analyzed. The results indicated that the Ca2(+)-ATPase activity reaches a peak at approximately pCa 4-5, and decreases at higher and lower Ca2+ concentrations. In the range of pCa 5-6, ATPase activity increases with Ca2+ concentration. Therefore, the model accounts for the kinetic properties of Ca2(+)-ATPase is a qualitative way. Moreover, it is proved that the Ca2+ dependence of Ca2(+)-ATPase activity is theoretically based upon the changes in Ca2+ affinity of Ca2+ binding sites and the Ca2+ dependence of Ca2(+)-ATPase activity is possibly involved in the regulation of intracellular Ca2+ concentration in vivo as a switching mechanism.

Biological Transport, Active↗
PubMed1990

Functional consequences of mutations of conserved amino acids in the beta-strand domain of the Ca2(+)-ATPase of sarcoplasmic reticulum.

The sequences Thr-Gly-Glu-Ser184 and Asp-Gln-Ser178 and individual residues Asp149, Asp157, and Asp162 in the sarcoplasmic reticulum Ca2(+)-ATPase are highly conserved throughout the family of cation-transporting ATPases. Mutant Thr181----Ala, Gly182----Ala, Glu183----Ala, and Glu183----Gln, created by in vitro mutagenesis, were devoid of Ca2+ transport activity. None of these mutations, however, affected phosphorylation of the enzyme by ATP in the presence of Ca2+ or by inorganic phosphate in the absence of Ca2+, indicating that the high affinity Ca2(+)-binding sites and the nucleotide-binding sites were intact. In each of these mutants, the ADP-sensitive phosphoenzyme intermediate (E1P) decayed to the ADP-insensitive form (E2P) very slowly relative to the wild-type enzyme, whereas E2P decayed at a rate similar to that of the wild-type enzyme. Thus, the inability of the mutants to transport Ca2+ was accounted for by an apparent block of the transport reaction at the E1P to E2P conformational transition. These results suggest that Thr181, Gly182, and Glu183 play essential roles in the conformational change between E1P and E2P. Mutation of Ser184, Asp157, or Ser178 had little or no effect on either Ca2+ transport activity or expression. Mutations of Asp149, Asp162, and Gln177, however, were poorly expressed. Where expression could be measured, in mutations to Asp162 and Gln177, Ca2+ transport activity was essentially equivalent to that of the wild-type enzyme.

Amino Acid Sequence↗
PubMed1990

Partial purification and characterization of the Ca2(+)-pumping ATPase of the liver plasma membrane.

A Ca2(+)-pumping ATPase has been characterized in rat hepatocyte plasma membranes. The enzyme has high Ca2+ affinity, and properties typical of a P-type ion pump. At variance with the Ca2+ pumps of other eukaryotic plasma membranes, it is not stimulated by calmodulin. The steady state concentration of the phosphoenzyme formed in the presence of ATP is increased by La3+. The enzyme cross-reacts with a monoclonal antibody (mAb-5F10) raised against the human erythrocyte Ca2+ pump. The enzyme has been purified using a mAb-5F10 antibody affinity column. CNBr digestion of the isolated protein has yielded two peptides which have been sequenced. One of them matches perfectly a sequence contained in the erythrocyte Ca2+ pump, the other is very homologous to another domain in the erythrocyte pump. In spite of the absence of calmodulin stimulation, 125I-calmodulin overlay experiments on the purified liver ATPase under denaturing conditions have revealed that the enzyme binds calmodulin even more strongly than the erythrocyte pump. Immunocytochemical experiments on liver slices using the mAb-5F10 antibody have shown that the enzyme is located predominantly in the blood sinusoidal domain of the hepatocyte plasma membrane.

Amino Acid Sequence↗
PubMedDate not supplied

[Reconstruction of purified Ca2+,Mg2+-ATPase from the myometrium sarcolemma into liposomes and its catalytic properties].

The Ca2+, Mg2(+)-ATPase of the myometrium sarcolemma purified by the method of affinity chromatography on calmodulin sepharose is reconstituted into azolectin liposomes in the functionally active form by means of cholate dialysis. The ATPase-dependent accumulation of 45Ca is shown on the obtained model system. It makes up 95% of the total accumulation and may decrease to 43% under the effect of 0.8 microM A23187. Ca2+, Mg2(+)-ATPase reconstituted into azolectin liposomes is in the high affinity to Ca2+; Km for Ca2+ is equal to 0.88 +/- 0.22 microM, calmodulin practically does not change it. The highest activity of the reconstituted enzyme is observed at pH 7.0, temperature 50 degrees C, the Mg-ATP concentration 1-2 mM. The Km for substrate is 0.45 +/- 0.02 mM.

Animals↗
PubMed1990

Lanthanum inhibits steady-state turnover of the sarcoplasmic reticulum calcium ATPase by replacing magnesium as the catalytic ion.

LaATP is shown to be an effective inhibitor of the calcium ATPase of sarcoplasmic reticulum because the binding of LaATP to cE.Ca2 results in the formation of lanthanum phosphoenzyme, which decays slowly. Steady-state activity of the calcium ATPase in leaky sarcoplasmic reticulum vesicles is inhibited 50% by 0.16 microM LaCl3 (15 nM free La3+, 21 nM LaATP) in the presence of 25 microM Ca2+ and 49 microM MgATP (5 mM MgSO4, 100 mM KCl, 40 mM 4-morpholinepropanesulfonic acid, pH 7.0, 25 degrees C). However, 50% inhibition of the uptake of 45Ca and phosphorylation by [gamma-32P]ATP in a single turnover experiment requires 100 microM LaCl3 (28 microM free La3+) in the presence of 25 microM Ca2+; this inhibition is reversed by calcium but inhibition of steady-state turnover is not. Therefore, binding of La3+ to the cytoplasmic calcium transport site is not responsible for the inhibition of steady-state ATPase activity. The addition of 6.7 microM LaCl3 (1.1 microM free La3+) has no effect on the rate of dephosphorylation of phosphoenzyme formed from MgATP and enzyme in leaky vesicles, while 6.7 mM CaCl2 slows the rate of phosphoenzyme hydrolysis as expected; 6.7 microM LaCl3 and 6.7 mM CaCl2 cause 95 and 98% inhibition of steady-state ATPase activity, respectively. This shows that inhibition of ATPase activity in the steady state is not caused by binding of La3+ to the intravesicular calcium transport site of the phosphoenzyme. Inhibition of ATPase activity by 2 microM LaCl3 (0.16 microM free La3+, 0.31 microM LaATP) requires greater than 5 s, which corresponds to approximately 50 turnovers, to reach a steady-state level of greater than or equal to 80% inhibition. Inhibition by La3+ is fully reversed by the addition of 0.55 mM CaCl2 and 0.50 mM EGTA; this reactivation is slow with t1/2 approximately 9 s. Two forms of phosphoenzyme are present in reactions that are partially inhibited by La3+: phosphoenzyme with Mg2+ at the catalytic site and phosphoenzyme with La3+ at the catalytic site, which undergo hydrolysis with observed rate constants of greater than 4 and 0.05 s-1, respectively. We conclude, therefore, that La3+ inhibits steady-state ATPase activity under these conditions by replacing Mg2+ as the catalytic ion for phosphoryl transfer. The slow development of inhibition corresponds to the accumulation of lanthanum phosphoenzyme. Initially, most of the enzyme catalyzes MgATP hydrolysis, but the fraction of enzyme with La3+ bound to the catalytic site gradually increases because lanthanum phosphoenzyme undergoes hydrolysis much more slowly than does magnesium phosphoenzyme.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphate↗
PubMed1979

Toxic substances and cell membrane function.

The exposed location and functional importance of cell membranes make them particularly susceptible to the toxic effects of many chemicals. The likelihood of such effects has been appreciated for many years. However, the recent advent of new techniques has greatly increased our understanding of the complexities of membrane structure and function. These data make it quite clear that the interaction of toxic compounds with either the protein or the lipid component of cell membranes may substantially alter membrane function. This paper summarizes the current concepts of membrane structure and function and discusses the techniques currently in use to study cell membranes. Several examples are presented in which xenobiotics significantly alter membrane function. These include effects of heavy metals on passive ion permeability, impairment of osmoregulation and calcium transport by organochlorine pesticides, inhibition of the transport of neurotransmitter metabolites by phenoxyacetic acid herbicides in choroid plexus, and reduction in intestinal nutrient transport by heavy metals. Hence the study of the interactions of foreign compounds with membrane function may enhance our understanding of mechanisms both of toxicity and of basic membrane function.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1979

Nerve cell calcium as a messenger for opiate and endorphin actions.

The studies outlined in this chapter provide convincing evidence for the role of calcium in pharmacological and biochemical actions of opiates on the central nervous system. The ability of the synaptosomes to accumulate excess calcium during narcotic exposure represents a singular major example of cellular adaptation at the level of the membrane. These findings together with the possibility that CDR and calcium may mediate a number of processes involving neurotransmitter activity provide many avenues for the future study of opiates and other central nervous system depressants.

Animals↗
PubMed1979

Na,K-ATPase in excitation-contraction coupling of vascular smooth muscle from cattle.

Lowering the extracellular K+ content from 6 to 0.6 mM causes a rise, and elevation from 6 to 8.5 mM a fall of 45Ca++ efflux from the vascular smooth muscle cells of the arteria carotis communis of cattle. In contrast, a level of 17 mM K+ has no influence. Removal of extracellular calcium does not block these effects. 10(-4) M ouabain also induces a rise in Ca++ efflux, additional potassium reduction then being without effect; 10(-9) M ouabain is of no influence. The 45Ca++ efflux kinetics correlates with the activity of the isolated Na,K-ATPase. Tonus increases of the vascular strips by 10(-4) M ouabain and potassium deficiency cannot be blocked by 4 mM lanthanum or removal of extracellular calcium. Unlike sodium, potassium stimulates the active Ca++ binding and the activity of the Ca-ATPase of the microsomal fraction. The ative Ca++ binding of the mitochondria is stimulated by both ions. It is postulated that the activity of the plasma membrane Na,K-pump is able to regulate the tonus of big arteries through alteration of Ca++ storage processes.

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↗