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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A method for investigating the microstruct and dynamics of biological systems by means of triplet-excited molecules is suggested. The method is based on the phenomenon of triplet excitation disactivation by exchange-resonance triplet-triplet energy transfer to the acceptor or by intercombination conversion induced by interaction of an excited molecule with a paramagnetic center. The disactivation efficiency was measured by registrating the phosphorescense decay kinetics. The interaction of the triplet label eosin isothiocyanate, covalently coupled with albumine, lysozyme, sarcoplasmic reticulum membrane and Ca-Mg-dependent sarcoplasmic reticulum ATPase, with O2, the stable nitroxide radicals and ions of Mn2+ was investigated to analyse the potentialities of this method. As a model system the eosin phosphorescence quenching by the same quenchers in glycerine-aguaous solutions was studied. The method permits to investigate the microviscosity and microstructure of biological objects in the label attached region on interaction of the label with a sound-quencher with constants being 10(4) divided by 10(9) M-1 sec-1 and to measure the lateral diffusion of molecules in highly viscosity media (10 divided by 10(5) santypuas).
Mol Biol (Mosk)
PMID:[Investigation of the microstructure of biological systems by triplet label]. 22 37

Plasma membrane fractions from normal, regenerating liver and the AS-30D ascites hepatocarcinoma exhibited a high degree of enrichment when a set of plasma membrane enzyme markers were studied in comparison to the ones associated to the mitochondrial and cytosolic compartments. While the (Ca2+, Mg2+)-ATPase observed for the plasma membrane fraction isolated from normal liver showed an activity of 1.2 mumoles/mg/min, the regenerating liver and the AS-30D plasma membrane fractions presented a much lower ATPase activity (0.3 and 0.22 mumoles/mg/min respectively). Despite the differences in ATPase activity observed between models, the plasma membrane fraction from the AS-30D hepatocarcinoma presented a calcium transport activity similar to the value observed for the normal system (5.9 and 5.5 nmoles Ca2+/mg/10 min, respectively). Interestingly, the ATP in equilibrium with Pi exchange experiments carried out with the different plasma membrane fractions revealed that the (Ca2+, Mg2+)-ATPase contained in the plasma membrane from the AS-30D cells shows an exchange activity of 26 nmoles ATP in equilibrium with Pi/mg/min, similar to the one observed fo the enzyme from normal liver (30 nmoles ATP in equilibrium with Pi/mg/min). Our results suggest that the plasma membrane from the transformed model presents a more efficient mechanism to regulate the movement of calcium through the calcium pump, with an optimum expenditure of energy.
Mol Cell Biochem 1991 Jan 16
PMID:Altered coupling states between calcium transport and (Ca2+, Mg2+)-ATPase in the AS-30D ascites hepatocarcinoma plasma membrane. 182 60

ATPase activity in rat heart sarcoplasmic reticulum was stimulated in a concentration-dependent manner by both Ca2+ and Mg2+ in the complete absence of the other cation. Increasing concentrations of Mg2+ produced an apparent inhibition of the Ca2(+)-dependent ATP hydrolysis. CDTA (trans-1,2-diaminocyclo-hexane-N,N,N',N'-tetraacetate) had no effect on these responses. The results indicate the presence of a low affinity non-specific divalent cation-stimulated ATPase in rat heart sarcoplasmic reticulum. However, sarcoplasmic reticulum vesicles transported Ca2+ with a high affinity (K0.5 Ca2+ = 0.41 microM) suggesting the presence of a high affinity Ca2(+)-transporting ATPase. Calmodulin did not stimulate rat heart sarcoplasmic reticulum ATPase activity over a range of Ca2+ and Mg2+ concentrations and failed to stimulate membrane phosphorylation and Ca2+ transport into sarcoplasmic reticulum vesicles. Calmodulin antagonists trifluoperazine and compound 48/80 did not affect the ATPase activity. Catalytic subunit of cAMP-dependent protein kinase was also ineffective in stimulating the ATPase activity. These results suggest the presence of an ATPase activity in rat heart sarcoplasmic reticulum with different properties from the high affinity Ca2(+)-pumping ATPase previously characterized in dog heart and other species.
Mol Cell Biochem 1990 Aug 10
PMID:A non-specific Ca2+ (or Mg2+)-stimulated ATPase in rat heart sarcoplasmic reticulum. 214 1

It has been proposed that oxygen free radical production is an important mediator of the myocardial dysfunction during the course of acute ischemia. We tested this hypothesis by characterizing the pathway of calcium efflux across sarcoplasmic reticulum (SR) membranes affected by oxygen free radicals. The effect of oxygen free radicals on the steady state calcium load, calcium permeability, and Ca,Mg-ATPase activity of isolated canine cardiac SR vesicles was investigated at pH 7.0. In vitro generation of oxygen free radicals by xanthine oxidase (0.09 units/ml), acting on xanthine in doses up to 50 microM as a substrate, increased the permeability of the SR vesicles to calcium, determined by measuring net efflux of calcium after stopping pump-mediated fluxes, and decreased total intravesicular calcium and free intravesicular calcium with no effect on Ca,Mg-ATPase activity. The effect of oxygen free radicals on calcium permeability was calcium gradient-dependent. Xanthine alone or xanthine plus denatured xanthine oxidase had no effect on this system. Superoxide dismutase (SOD, 56 units/ml), but not denatured SOD, significantly inhibited the effect of xanthine-xanthine oxidase reaction. The calcium permeability of the SR membrane decreased with decreasing calcium load. In addition, inasmuch as extravesicular calcium exerts only a slight effect on calcium permeability, the decrease in the permeability with calcium load is specifically related to the calcium load. Oxygen free radical-induced increase in calcium permeability was unaffected by Mg concentration between 2.1 and 21 mM. In summary, our data reveal that .O2- can produce a diminished level of accumulated calcium, which is reflected by the decreased calcium load and an increase in passive calcium permeability, and that the decreased calcium accumulation in the presence of the xanthine-xanthine oxidase system may not be mainly due to an inhibited calcium pump but due to an increased calcium permeability. Our results also suggest that increased SR membrane passive calcium permeability induced by oxygen free radicals is not carrier mediated. It is postulated that, with the oxygen free radical-mediated progressive increase in calcium permeability, free cytosolic calcium concentrations would increase in ischemic myocardium.
Mol Pharmacol 1988 Sep
PMID:The effect of oxygen free radicals on calcium permeability and calcium loading at steady state in cardiac sarcoplasmic reticulum. 284 52

Canine cardiac sarcoplasmic reticulum is phosphorylated by adenosine 3',5'-monophosphate (cAMP)-dependent and by calcium.calmodulin-dependent protein kinases on a 27,000 proteolipid, called phospholamban. Both types of phosphorylation are associated with an increase in the initial rates of Ca2+ transport by SR vesicles which reflects an increased turnover of elementary steps of the calcium ATPase reaction sequence. The stimulatory effects of the protein kinases on the calcium pump may be reversed by an endogenous protein phosphatase, which can dephosphorylate both the cAMP-dependent and the calcium.calmodulin-dependent sites on phospholamban. Thus, the calcium pump in cardiac sarcoplasmic reticulum appears to be under reversible regulation mediated by protein kinases and protein phosphatases.
Mol Cell Biochem
PMID:The role of protein kinases and protein phosphatases in the regulation of cardiac sarcoplasmic reticulum function. 284 12

Ontogenetic changes in calcium transport mediated by the sarcolemmal Na-Ca exchanger and by the sarcoplasmic reticulum calcium pump were studied in crude membranes from chick heart. Transport activities were evaluated per mass of membrane protein and heart tissue. Relative to unit heart mass Na-Ca exchange activity increases linearly from embryonic day 4 to day 10 of newborn stage. The overall increase is about 20-fold. An excellent correlation exists between activity of sodium gradient-induced calcium uptake and ouabain-sensitive (Na,K)-ATPase in crude membranes of embryonic, newborn and adult hearts. In the same membrane preparations active calcium uptake into vesicles of sarcoplasmic reticulum increases about 3-fold from embryonic day 4 to embryonic day 7, and then increases continuously until day 20. This is followed by a 3-fold elevation in reticular calcium accumulation at hatching on day 21. Maximal sarcoplasmic reticulum calcium transport activity reached at day 10 after hatching is 40- to 50-fold greater than activity values at embryonic day 4. In adult hearts the activities of both Na-Ca exchange and reticular calcium uptake drop to levels characteristic for the late embryonic period. This comparative study of sarcolemmal sodium gradient-dependent calcium flux and reticular calcium sequestration demonstrates that during chick heart differentiation the two calcium transport systems do not develop in parallel. Na-Ca exchange appears to play a greater role in calcium control of embryonic as compared to newborn and adult hearts. By contrast, the contribution of sarcoplasmic reticulum calcium transport to cardiac calcium movements becomes more predominant during and after hatching.
J Mol Cell Cardiol 1986 Dec
PMID:Sarcolemmal Na-Ca exchange and sarcoplasmic reticulum calcium uptake in developing chick heart. 302 91

The effect of cAMP-dependent protein kinase on calcium uptake and protein phosphorylation in bovine aortic microsomes was examined. Acid gel electrophoresis demonstrated that the aortic microsomes contained a Ca2+-dependent, hydroxylamine-sensitive phosphoenzyme (Mr 110 kDa), characteristic of the calcium pump in sarcoplasmic reticulum, but showed no evidence of a sarcolemmal calcium pump. Calcium uptake by these aortic vesicles was markedly stimulated by oxalate, whereas calcium uptake by canine cardiac sarcolemmal vesicles was oxalate-independent. Both cAMP plus protein kinase (cAMP-PK) and catalytic subunit of protein kinase stimulated oxalate-supported calcium uptake by bovine aortic microsomes 23 +/- 3% (P less than 0.05) at 0.3 microM Ca2+, but had no effect at 6 to 10 microM Ca2+. Catalytic subunit of protein kinase and cAMP-PK phosphorylated an 11 kDa protein in bovine aortic microsomes which comigrated with canine cardiac phospholamban after boiling in sodium dodecylsulfate. The stoichiometry of the aortic 11 kDa phosphoprotein to 110 kDa phosphoenzyme was approximately 1:1. These data are consistent with the recent identification of phospholamban in various smooth muscles, and suggest that cAMP-mediated vascular relaxation may in part be attributable to stimulation of calcium uptake by the sarcoplasmic reticulum.
J Mol Cell Cardiol 1988 Aug
PMID:Regulation of calcium uptake in bovine aortic sarcoplasmic reticulum by cyclic AMP-dependent protein kinase. 322 9

The nonspecific interaction of the beta-adrenergic blocking drugs, propranolol and timolol, with model and biological membranes has been investigated. Radioisotope measurements of the association of these drugs with dimyristoyl lecithin (DMPC) bilayers showed that both propranolol and timolol had a significantly greater molar association (mole of drug per mole of lipid) with DMPC above its phase transition temperature than below. Timolol had a much lower molar association with DMPC as compared with propranolol both above and below the phase transition temperature. For the DMPC model membrane system, the molar association of propranolol as measured by radioisotope and inferred from calorimetric studies was similar. Neutron diffraction utilizing propranolol deuterated in the naphthalene moiety showed that the naphthalene moiety of propranolol partitions into the hydrocarbon core of the DMPC lipid bilayer, and that the charged amine side chain is most likely positioned in the aqueous phospholipid head group region. For timolol, the association as measured by radioisotope methods was apparently greater than the partitioning inferred from calorimetric studies using freezing point depression analysis, suggesting a more complex interaction of timolol as compared with propranolol with the DMPC lipid bilayer. The association of propranolol and timolol with sarcoplasmic reticulum vesicles (SR) was similar to that with highly purified protein-depleted SR lipids, and DMPC above its phase transition. The association of propranolol with the SR membrane (mole of propranolol per mole of SR phospholipid) correlated with its ability to inhibit calcium uptake, whereas only a fraction of the total association of timolol with the SR membrane appeared to lead to inhibition of calcium uptake. These results suggest that the major nonspecific interactions of propranolol and timolol are with the SR membrane lipids, and that the magnitude of their interactions depends on both the lipid solubility of the drug and the physical state of the fatty acyl chains of the membrane. Both propranolol and timolol appear to perturb the functional properties of the calcium pump protein in the SR membrane (inhibition of ATP-induced calcium uptake) indirectly by partitioning into the bulk lipid matrix of the SR lipid bilayer, although other sites of interaction cannot be excluded.
Mol Pharmacol 1983 Sep
PMID:Comparisons of the interaction of propranolol and timolol with model and biological membrane systems. 688 69

Secretion of parathyroid hormone-related protein (PTHrP) by sheep fetal parathyroid glands is reported to be an important factor in the maintenance of a placental calcium pump. The aim of the present study was to determine whether the developing rat parathyroid glands express PTHrP or parathyroid hormone (PTH), or both. Hybridisation histochemistry was used to detect transcription of PTHrP and PTH in serial paraffin sections through the 12.5- and 13.5-day rat embryo parathyroid anlage, as well as in sections through the 17.5-day embryonic and adult parathyroid glands. Results show strong expression of PTH in the 13.5-day embryonic parathyroid anlage, as well as in the parathyroid gland of the 17.5-day embryo and adult. Transcription of the PTHrP gene was not detected. The more sensitive technique of reverse transcription PCR was then performed. The pharyngeal region of 11.5-, 12.5- and 13.5-day rat embryos was dissected out and, at each stage, RNA was extracted from these tissues, as well as pooled tissues from the rest of the embryo. RNA that had been extracted from adult thyroid/parathyroid tissue was also tested. After reverse transcription, the resulting cDNAs were amplified by PCR (50 cycles) using specific PTH and PTHrP primers. The results show an abundance of PTH mRNA, specific to the pharyngeal region of the 13.5-day embryo, as well as to adult thyroid/parathyroid tissue. PTHrP expression was detected at very low levels in both parathyroid and extraparathyroid tissues. The presence of immunoreactive PTHrP and immunoreactive PTH in the pharyngeal region and rest of the body of 12.5- and 13.5-day rat embryos was assessed by specific RIAs. Whilst immunoreactive PTHrP was not detected in any of the tissues assayed, immunoreactive PTH was detected only in the pharyngeal region of the 13.5-day embryo. This confirms the results obtained from the gene expression studies. We conclude then that, in the developing rat embryo, PTH rather than PTHrP is more likely to play a role in calcium regulation. This is in contrast with the reported situation in the sheep, and suggests that fundamental species differences in fetal calcium regulation exist in mammals.
J Mol Endocrinol 1996 Oct
PMID:The expression of parathyroid hormone and parathyroid hormone-related protein in developing rat parathyroid glands. 893 90

During pregnancy, a placental calcium pump maintains the fetus in a hypercalcaemic state relative to the mother, a condition which has been thought to facilitate normal development of the fetal skeleton. Based on experiments performed in the sheep, parathyroid hormone-related protein (PTHrP) has been implicated as the hormone responsible for maintaining the placental calcium pump. In the present study on mice in which the PTHrP gene has been ablated by homologous recombination, we have measured both fetal and maternal circulating total and ionised calcium levels, as well as fetal total body calcium, in order to determine whether absence of PTHrP during fetal development has an effect on fetal calcium levels. Our results show that, in fetuses lacking PTHrP, circulating ionised calcium levels are significantly lower than those of heterozygote and wild-type littermates, but circulating total calcium levels show no difference. Total body calcium levels of null mutants are significantly higher than those of normal littermates. The role of PTHrP in maintaining the integrity of the transplacental calcium pump in the rodent thus remains unclear. It may be that the lower levels of fetal blood ionised calcium in mutant animals are due to disruption of the placental pump, but, if this is the case, compensatory mechanisms have operated to allow the excessive calcium deposition seen in the skeletons of these animals. Alternatively, the increased avidity of the bones for calcium may in itself have produced a lower equilibrium level of available ionised calcium.
J Mol Endocrinol 1996 Oct
PMID:The role of fetal parathyroid hormone-related protein in transplacental calcium transport. 893 91


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