The determination of the separate Ca2+ pump protein and phospholipid profile structures within reconstituted sarcoplasmic reticulum membranes via X-ray and neutron diffraction

We have previously compared the electron density profiles for several highly-functional reconstituted sarcoplasmic reticulum membranes with that for the isolated sarcoplasmic reticulum membrane (Herbette, L., Scarpa, A., Blasie, J.K., Wang, C.T., Saito, A. and Fleischer, S. (1981) Biophys. J. 36, 47-72). In this paper, we compare the separate calcium pump protein profile within these reconstituted sarcoplasmic reticulum membranes, as derived by X-ray and neutron diffraction methods, with that within isolated sarcoplasmic reticulum membranes. In addition, the time-average perturbation of the lipid bilayer by the incorporated calcium pump protein within these reconstituted sarcoplasmic reticulum membranes has been determined in some detail.

Stimulation of calcium pump activity in heart sarcolemma by timolol

The effects of beta-adrenergic blocking agents, timolol and atenolol (1-1000 microM), were studied on rat heart sarcolemmal ATPase and Ca2+ binding activities. Timolol, unlike atenolol, increased both Ca2+-stimulated ATPase and ATP-dependent Ca2+ binding; the maximal effects were seen at 1 microM concentration of timolol. Both timolol and atenolol did not alter the sarcolemmal Mg2+ ATPase and nonspecific Ca2+ binding activities. Sarcolemmal Ca2+-stimulated ATPase was also activated by concanavalin A (6-66 micrograms/mL) which is known to alter membrane fluidity; however, Mg2+ ATPase was unaffected by this agent. These results indicate that timolol may stimulate Ca2+ pump activity in heart sarcolemma by changing membrane fluidity in a manner similar to that of concanavalin A.

Effects of vanadate on isolated vascular tissue: biochemical and functional investigations

Vanadate is a potent inhibitor of Na+,K+-ATPase derived from bovine aorta. The Ca2+, Mg2+-ATPase of the same preparation was inhibited at 10 times higher concentrations. Compared with [3H]ouabain, 48V bound quickly to bovine aortic microsomes. Equilibrium binding experiments revealed one high-affinity, low-capacity and one low-affinity binding site for 48V, whereas [3H]ouabain possessed only one binding site of high affinity. A high NADH-vanadate reductase activity was measured in the same preparation, suggesting that, in this tissue, vanadate may be converted to vanadyl, a form to which the Na+,K+-ATPase is relatively insensitive. An increase in the contractile force of isolated rabbit aorta was measured with the following potency: phenylephrine greater than ouabain greater than vanadate. The order in intrinsic activity was as follows: phenylephrine congruent to ouabain greater than vanadate. The action of vanadate was rapid in onset and stable over several hours, while that of ouabain was slow and transitory. Vanadate increased tension in isolated rabbit veins to an extent similar to phenylephrine, but at concentrations two orders of magnitude higher. Vanadate action decreased with decreasing (Ca2+)0, but remained constant at a constant ratio of (Ca2+)0/(Na+)2(0). Vanadate-induced increases in tension were decreased by verapamil by about 43% and persisted in a solution in which Na+ was replaced by Li+. Vanadate increased electrically stimulated contractions. It is concluded that most of the effect of vanadate is due to an increase in calcium influx into the smooth muscle cell and that the effect of vanadate on Na+,Ca2+ exchange is of minor importance.

Altered property of sarcoplasmic Ca-ATPase from vitamin E-deficient dystrophic rabbit is associated with the protein and not the lipid component

The effects of temperature on reconstituted sarcoplasmic Ca-ATPase preparations from vitamin E-deficient dystrophic and control rabbits were studied. Delipidated Ca-ATPase from vitamin E-deficient sarcoplasmic reticulum (SR) reconstituted with lipid of control SR exhibited properties similar to preparations reconstituted with lipid of vitamin E-deficient SR, namely low Ca-ATPase activity and a linear Arrhenius plot of enzyme activity. On the other hand, delipidated control SR Ca-ATPase reconstituted with lipid of vitamin E-deficient SR showed a reduction in activity but retained the discontinuity in the Arrhenius plot. These results indicated that the altered property of sarcoplasmic Ca-ATPase from vitamin E-deficient dystrophic rabbit was associated with the protein and not the lipid component.

Analytical subcellular fractionation of normal human skeletal muscle by sucrose density gradient centrifugation

The principle organelle marker enzymes and various adenosine triphosphatase (ATPase) activities were studied in human skeletal muscle. The reproducibility of each assay was established under optimal and linear assay conditions. Whole homogenates of normal human quadriceps muscle were fractionated by centrifugation on a continuous sucrose density gradient. Gradient fractions were assayed for organelle marker enzymes and frequency-density histograms were constructed for each enzyme. Good resolution of the principal organelles was obtained. Adenosine triphosphatase (ATPase) was assayed under conditions of maximal stimulation by Ca2+, or Mg2+ or Na2+, K+ + Mg2+. The distribution of these activities was compared with those of the organelle marker enzymes. Both Ca2+-ATPase and Mg2+-ATPase were distributed to both the mitochondrial and myofibrillar fractions but could be distinguished by the inhibition of mitochondrial ATPase with sodium azide. The distribution of Na+, K+-activated, Mg2+-dependent ATPase (Na+, K+ ATPase) activity suggested a sarcolemmal localization. The results of electron microscopy of gradient fractions were consistent with the organelle content of the fractions as determined by enzymic analyses. These studies provide reference information for the subsequent investigation of organelle pathology of human muscle disorders.

Phylogenetic studies of cardiac myosins from amphibia to mammals

Comparison between pig atrial and ventricular myosins was performed on the light chains (using SDS-PAGE) and on the heavy chains (using Ca2+-ATPase measurements and NTCBA peptide mapping). Light chain composition of pig cardiac myosins was compared to three other species ones (frog, chicken and human). Up to birds, atrial and ventricular myosin light chain composition was identical whereas in mammals atrial and ventricular myosin light chain composition was different; likewise the heavy chains. Six cardiac myosin isoenzymes have been thus characterized. No correlation can be established between cardiac myosin light chain pattern and species evolution.

Effect of 1,25-dihydroxycholecalciferol on sarcoplasmic reticulum calcium transport in strontium-fed chicks

Feeding of chicks with strontium, an inhibitor of 1,25-dihydroxycholecalciferol synthesis in kidney, during 7 days, significantly depressed the initial rate of calcium uptake and calcium storing capacity of sarcoplasmic reticulum membranes from skeletal muscle. Oral administration of 1,25(OH)2D3 to strontium-fed animals returned calcium transport values to normal. The changes observed could not be related to differences in the relative proportions of transport ATPase and calcium binding proteins. The results are consistent with a role of 1,25(OH)2D3 in muscle function.

[Effect of temperature on fluorescence of labels and probes of various localizations incorporated into sarcoplasmic reticulum samples]

Studies were carried out of temperature relationship of dansylchloride, N-3-pyrenylmaleinimide fluorescence, SR membranes, self-luminescence caused by Ca-ATPase tryptophane - provided fluorescence and of pyrene excimerization in membrane preparations of sarcoplasmic reticulum (SR) of rabbit skeletal muscles. Temperature relationship of fluorescence intensity of dansylchloride and N-3-pyrenylmaleimide in Arrhenius coordinates has bends at 15 and 35 degrees. Selffluorescence of protein samples linearly depends on temperature. Temperature relationship of the ratio between the intensities of exsimeric and monomeric forms of pyrene Fa/Fm in Arrhenius coordinates has the bend at 20-22 degrees. Hence only the latter relationship coincides with the shape of Arrhenius graph for enzymatic activity of SR Ca-ATPase.

Reconstitution of heavy chain and light chain 1 in cardiac subfragment-1 from hyperthyroid and euthyroid rabbit hearts

It is now established that cardiac myosin from hyperthyroid rabbit hearts (TXM) exhibits high Ca2+ ATPase activity. The high Ca2+ ATPase activity of TXM was completely retained in cardiac myosin subfragment-1 (S-1) (1.33 +/- 0.04 mumol Pi/mg per min; euthyroid, 0.51 +/- 0.04). Cardiac S-1 from hyperthyroid and euthyroid rabbits (TXS-1 and NS-1) had the same pattern in SDS-polyacrylamide gel electrophoresis. The possible influence of heavy and light chains of TXM on increasing the ATPase activity was examined by reconstitution in the S-1 preparation. Crosswise reconstitution was performed using cardiac S-1 heavy chain (90,000 daltons) and light chain 1 (LC1) (27,000 daltons) from hyperthyroid and euthyroid hearts. Reconstitution was verified by using radiolabeled LC1. More than 95% of S-1 was recovered with full ATPase activity. When TXS-1 was reconstituted with LC1 from euthyroid hearts, the reconstituted molecule retained high ATPase activity. On the other hand, NS-1 reconstituted with LC1 from hyperthyroid hearts failed to increase the ATPase activity. The ATPase activity of S-1 was determined by the source of the heavy chain. These results suggest that the high Ca2+ ATPase activity of cardiac myosin and S-1 from hyperthyroid animals arises from the molecular alteration of the heavy chain induced by thyroxine administration.

Discrimination and consistency of five myosin ATPase stains in human normal and Duchenne dystrophic muscle

Limitations in the ability of the human visual system to assess accurately the relative staining densities of individual fibers in muscle tissue stained for myosin. ATPase can complicate the objective evaluation of fiber type populations. In this study a novel approach is employed which utilizes human visual capabilities to provide accurate fiber classification. Using this approach, the ability of five ATPase staining techniques to discriminate fiber type categories in single samples of human normal and Duchenne dystrophic skeletal muscle is evaluated, as is the consistency of the fiber type classifications between stains. While no major discrepancies in fiber typing were observed in the sample of normal muscle, significant differences in classification, along with a decrease in the ability to discriminate fiber types were noted in the sample of Duchenne muscular dystrophy. For the most part, these discrepancies were resolved by a re-interpretation of the staining characteristics of fibers in one stain.

Structure and function of the calcium pump protein of sarcoplasmic reticulum

Recent developments concerning the structure and function of the Ca2+ pump protein of the sarcoplasmic reticulum have been briefly reviewed. Various new methods have become available that make it possible to monitor dynamic changes in the structure of the enzyme molecule associated with elementary steps of the enzyme reaction. In the light of information about chemical reactivity of various amino acid residues and their location in the primary structure of the ATPase polypeptide, it will be fruitful to use extrinsic conformational probes placed at specific locations to monitor the kinetics of the enzyme. Furthermore, a growing body of evidence suggests that subunit-subunit interactions of an oligomeric Ca2+ ATPase are involved in the regulation of the kinetics of the enzyme. Thus the kinetic mechanisms has to be reinterpreted at all levels--i.e. primary, secondary, tertiary, and quaternary--of structure.

Transitions in membrane composition during postnatal development of rabbit fast muscle

Early postnatal changes (4-5 days to 15 days after birth) in the biochemical composition of microsomes were investigated in rabbit skeletal muscles destined to become fast-twitch muscles. During this period, a steady decrease in the microsomal content of cholesterol and of ouabain-sensitive Na + /K + -ATPase activity, as well as a decrease in protein electrophoretic components in the 80 000-70 000 molecular weight range, were observed. These changes are probably due to a diminishing yield of microsomal membranes derived from T-tubules, as the age of the animals increases, and are indicated from a knowledge of the mixed composition of muscle microsomes and previous biochemical data on isolated T-tubules. The content of cytochrome b5, which was found to be high in muscle microsomes of newborn animals, decreased strikingly as the amount of membrane-bound Ca2 + -ATPase protein increased, with a crossing-over point at about 7-10 days after birth. These changes, possibly corresponding to a transition from precursor sarcoplasmic reticulum (SR) to mature SR, were found to be temporally correlated with changes in [3H] alpha-tocopherol binding ability of the microsomes and in the mitochondrial content of glycerol phosphate dehydrogenase. At the same critical periods, coincident with the onset of motile activity, the immunological cross-reactivity of the Ca2 + -ATPase protein of microsomal vesicles, with antibody specific for the Ca2 + -ATPase of adult fast SR, was found to increase markedly, as tested by competitive enzyme-linked immunosorbent assay (ELISA). The immunological data are consistent with data in the literature demonstrating an increase in the concentration of Ca2 + -ATPase molecules in the SR membranes during ontogenic development. Both these data and catalytic data, however, suggest that the Ca2 + -ATPase protein is present in the same form in the SR of immature and of adult fast muscle and, in an antigenically different form, in slow muscle SR.

Adenosine triphosphatases in electroreceptor organs (ampullary organs and mormyromasts) of Gnathonemus petersii Mormyridae

Cytochemical techniques were used for the light and electron microscopical localization of ATPase in the ampullary organ and the mormyromast, both cutaneous electroreceptors in Gnathonemus petersii (Mormyridae). At the right microscope level, two different techniques gave the same results, namely that high concentrations of the enzyme are present in the mormyromast and certain epidermal cells and weak concentrations in the ampullary organ. The enzyme was localized at the ultrastructural level using the lead capture method. It was found in the cytoplasm of type III accessory cells of the ampullary organ, in the apical cytoplasm of SC1 sensory cells and the accessory cells surrounding them and on the membrane of the SC2 sensory cells of the mormyromast. The ATPase of these various cells was inhibited by p-chloromercuribenzoate. The enzyme in the mormyromast SC1 and their accessory cells was not dependent on Mg2+ ions. However, that in the type III accessory cells of the ampullary organ and in the SC2 of the mormyromast was strictly dependent on Mg2+. In addition, there was a Ca2+-dependent ATPase in the microvilli of the SC2 of certain mormyromasts.

The sarcoplasmic reticulum of an ultrafast lobster muscle: first evidence of a tubular configuration

The sarcoplasmic reticulum (SR) of the remarkably fast remotor muscle of lobster second antenna was investigated with regard to ultrastructure, calcium uptake and protein composition. The SR of this unique muscle dominates the volume of the cell. We were able to preserve the configuration of the SR in its native state simply by processing the muscle for electron microscopy at 0-4 degree C. For the first time the SR is seen as larger (0.1 micrometer diam.) tubules that crowd the space between myofibrils, Previous observations of this organelle have been reported that showed a rather unsatisfying discontinuous vesicular configuration of the SR. This report indicates that these structures were fixation artifacts. The uptake of calcium measured in a microsomal subfraction in the presence of ATP and oxalate does not differ significantly from similar experiments with vertebrate SR. However, gel electrophoresis of lobster SR demonstrate a single intrinsic Ca-ATPase protein of 100,000 mol, wt. with neither of the typical lower molecular weight proteins found in vertebrate SR.

Phosphate and vanadate reduce the efficiency of the chemo-mechanical energy transformation in cardiac muscle

Trabecular preparations from the hog heart right ventricle were "skinned" by treatment with Lubrol WX and glycerol. Ca++ activated isometric contractions were gradedly relaxed by inorganic phosphate (Pi) in the millimolar range or vanadate (Vi) in the micromolar range while tension cost (ATP split/force generated) was increased by a factor of 1.75. From measurements of force, ATPase activity, immediate stiffness and stretch activation, evidence is provided that the mechanical deactivation and the increase in tension cost may result from an acceleration of the myosin cross-bridge cycle, due to a direct interference of Pi and Vi with the chemomechanical energy transformation at the contractile proteins. The possible significance of such a mechanism in cardiac failure or muscle fatigue is discussed.

Visualization of nucleolar substructure in cultured human fibroblasts by magnesium-activated adenosine triphosphatase reaction

Discrete sites of adenosine triphosphatase (ATPase) activity were demonstrated within the nucleoli of unfixed cultured human fibroblasts (IMR90, VA13, and AG2804 cells) by an adaptation, for electron microscopic cyto-chemistry, of Wachstein and Meisel's lead nitrate method. The majority of nucleoli contained more than one ATPase-positive region, but the total ATPase-positive material appeared to occupy only a minor portion of the nucleolar volume. These regions were roughly spherical with an irregular contour, and at times appeared to be components of perinucleolar chromatin or to be located adjacent to nucleolar interstices. The distribution of these regions within the nucleolus and their segregation by actinomycin D suggested that the ATPase-positive regions correspond to the fibrillar centers, which represent nucleolar organizer regions. The cytochemically demonstrable nucleolar ATPase was strictly dependent on the presence of divalent cations. Optimal reactions was seen at 5 mM Mg2+, but near optimal activity was obtained with lower concentrations of Mg2+ in the presence of Ca2+. Calcium alone and Mn2+ alone produced suboptimal reaction. Studies with different nucleoside phosphates as reaction substrates showed that the enzyme is specific for adenosine derivatives, ATP and dATP being equally good substrates. Guanosine triphosphate, cytidine triphosphate, uridine triphosphate, and d-thymidine triphosphate were ineffective as substrates, as were nucleoside mono- and diphosphates and other phosphate esters tested. It is suggested that the cytochemical ATPase reaction visualized the regions of the nucleolus in which ribosomal DNA of intranucleolar chromatin is undergoing conformational alterations.

Freeze-fracture study of water-soluble, standard proteins and of detergent-solubilized forms of sarcoplasmic reticulum Ca2+-ATPase

Conventional freeze-fracturing electron microscopy was used to study water-soluble proteins and different forms of Ca2+-ATPase-detergent complexes. Freeze-fracture images of solutions containing proteins larger than myoglobin showed the presence of distinct, randomly dispersed particles on smooth fracture surfaces. The distribution of sizes of these particles was closely to Gaussian, with a mean size which was correlated to the Stokes diameter. Monomeric Ca2+-ATPase from sarcoplasmic reticulum, solubilized by deoxycholate or a non-ionic detergent, showed a bimodal distribution of particle sizes. Even more complex distributions were found for dimeric and trimeric preparations of Ca2+-ATPase. The results can be interpreted on the assumption that the Ca2+-ATPase molecule is elongated, with an overall length of about 110 A and a width in its largest part of about 75 A. It is concluded on the basis of the presented results that freeze-fracture electron microscopy can be successfully used for morphological studies of protein molecules in solution.

A spin-label study of protein-lipid interaction in sarcoplasmic reticulum of rabbit skeletal muscle

Whether or not the thermotropic change at about 18 degrees C in the physical state of Ca2+-ATPase protein molecules of sarcoplasmic reticulum membranes could be transmitted to lipids through protein-lipid interactions was investigated using a spin-label technique. Fatty acid spin labels were used to probe the bulk membrane lipids while long-chain spin labels attached at one end to the Ca2+-ATPase molecules through a covalent bond were used to monitor the boundary lipids. The results on the temperature-dependence of alkyl-chain flexibility of lipid molecules indicate that the change in the state of the protein molecules is accompanied by one of the boundary lipids, but not of the bulk lipids.

The effects of nonidet P40 on the function of rat peritoneal mast cells in vitro

1 Treatment of purified rat peritoneal mast cells at 37 degrees C with concentrations of the non-ionic detergent nonidet P40 (NP40) up to 0.005% (v/v) failed to reduce their viability. 2 There was a marked reduction in the histamine releasing capacity of NP40-treated mast cells upon challenge with a variety of selective (adrenocorticotrophic hormone 1-24 (Synacthen), rabbit anti-rat IgE antiserum, adenosine triphosphate (ATP) and the calcium ionophore, A 23187) and non-selective (rabbit anti-rat mast cell antiserum plus complement) histamine liberators. 3 Nonidet P40 (0.005%) was found to reduce the activity of a mast cell membrane 'ecto-enzyme', calcium-activated ATPase, by about 45% when presented at the time of its assay.

Properties of detergent-solubilized and membranous (Ca2+ + Mg2+)-activated ATPase from sarcoplasmic reticulum as studied by sulfhydryl reactivity and ESR spectroscopy. Effect of protein-protein interactions

(1) Sulfhydryl reactivity and electron spin resonance spectra of nitroxide maleimide spin labels, covalently attached to sarcoplasmic reticulum ATPase, were examined on both detergent-solubilized and membranous material. Monomeric and oligomeric ATPases were prepared by the use of dodecyloctaethylene glycol monoether as a solubilizing detergent. (2) Immediately after solubilization, the reaction curve of nonomeric ATPase with 5,5'-dithiobis(2-nitrobenzoate) was characterized by positive cooperativity (S-shaped as a function of time). In contrast, the SH reactivity of both oligomeric and membranous ATPases obeyed usual first-order kinetics and could be analyzed in terms of three classes of reactive site. All enzymatically active ATPase preparations responded to addition of ADP with a decrease in SH reactivity. During enzymatic inactivation of monomeric ATPase, the SH-modification rate was dramatically enhanced with loss of cooperative features. Ca2+ removal from the high-affinity sites stimulated SH reactivity before inactivation had taken place. (3) ESR spectroscopy indicated less motional constraints on monomeric than on oligomeric and membranous ATPases. Arrhenius plots of ESR spectral parameters suggest a conformational transition in both membranous and solubilized ATPases at about 22 degrees C. The transition was also present in EGTA-, but not in heat-inactivated ATPase. Although SH reactivity of monomeric ATPase was dramatically enhanced by EGTA inactivation, the results of ESR, circular dichroism and analytical ultracentrifugation experiments indicate limited conformational changes induced by EGTA treatment. (4) The data indicate marked differences in the properties of monomeric ATPase on the one hand and oligomeric and membranous enzymes on the other hand. They are consistent with previous functional evidence for the presence of ATPase in an associated state in the membrane (Møller, J.V., Lind, K.E. and Andersen, J.P. (1980) J. Biol. Chem. 255, 1912-1920).

The effect of verapamil on the Ca2+-transporting and Ca2+-ATPase activity of isolated cardiac sarcolemmal preparations

1 The effect of (+/-)-, (+)- and (-)-verapamil on the Ca2+-binding, Ca2+-transporting activity, and Ca2+-dependent adenosine triphosphatase (ATPase) activity of isolated cardiac sarcolemmal preparations was studied. Enzymatic treatment was used to establish the nature of the sites facilitating [14C]-(+/-)-verapamil binding. 2 (+/-)-Verapamil 1 microM inhibited the passive binding of 45Ca2+. The (+/-)- and (-)-isomers were equiactive. 3 (+/-)-Verapamil 1 microM inhibited the ATP-dependent transport of 45Ca2+ and the associated activation of the Ca2+-sensitive ATPase. The activity resided in the (-)-isomer. 4 Lineweaver-Burk plots for the initial rates of ATP-dependent transport showed that the inhibition induced by the (-)-isomer was accompanied by a reduced Km and Vmax. 5 Enzymatic removal of N-acetyl neuraminic acid and galactose residues increased [14C]-(+/-)-verapamil binding; removal of N-acetylglucosamine and treatment with phospholipase C and trypsin decreased the binding. 6 These results have been interpreted to mean that (-)-verapamil interferes with the ATP-dependent Ca2+-transporting properties of the sarcolemma, and that this effect is accompanied by an altered activity of the intrinsic Ca2+-sensitive ATPase. N-acetylneuramic acid and galactose residues do not provide binding sites for verapamil at the cell surface.

Ion pathways in proteins of the sarcoplasmic reticulum

In summary, we have begun to characterize three different ion pathways in the sarcoplasmic reticulum. Ca2+-ionophoric activity has been traced to a 13,000-dalton CNBr fragment localized at the amino terminus of the ATPase molecule... The pathway involved in Ca2+ release can be distinguished from the pathway involved in Ca2+ uptake by its insensitivity to quercetin. An anion pathway is sensitive to DIDS and appears to be localized in the ATPase molecule

Purification and characterization of the proteolipid of rabbit sarcoplasmic reticulum

The proteolipid of rabbit sarcoplasmic reticulum was isolated and characterized. Tyrosine was identified as the C-terminal amino acid by hydrazinolysis and carboxypeptidase A digestion. The N-terminal sequence of proteolipid is: Met-Glx-Arg-Ser-Thr-Arg-Glx-Leu-Cys-Leu-Asp-Phe. The hydrophilic character of the N-terminal portion suggests that it is exposed on the membrane surface.

Isolation and characterization of secretory vesicles from bovine neurohypophyses

A procedure is described for the isolation of secretory vesicles from bovine neurohypophyses by differential centrifugation followed by density gradient centrifugation on iso-osmolal gradients of percoll/sucrose. Only negligible contamination of the secretory vesicle fraction with markers for mitochondria, microsomes and plasma membranes could be detected. The amount of Ca2-ATPase in the isolated neurohypophysial secretory vesicles was of the same low order of magnitude as that of (Na, K)-ATPase. Thin-section electromicrographs confirmed the high purity of the isolated secretory vesicle fractions, In freeze-fracture electronmicrographs, vesicle fusion was demonstrated after incubation with Ca2. As shown in dodecyl sulfate-gel electrophoresis and subsequent autoradiography secretory vesicles exhibited an endogenous phosphorylation activity. The secretory vesicles contained an average of 23.1 microgram vasopressin/mg of protein. On incubation in media differing in ionic strength, pH and Ca2 concentration the vesicles were stable for at least 1 h.

Activities of Ca2+-ATPase and Na+ + K+-ATPase in human placenta

Although there have been a few reports on Ca2+-ATPase and Na+ + K+-ATPase in human placenta, they are still insufficient for getting more detailed information about human placenta. In this study we investigated some characteristics of the Ca2+-ATPase and measured the activity of Ca2+-ATPase and Na+ + K+-ATPase at various gestational periods. Maximum activity of Ca2+-ATPase was seen at 3 mM and pH 9.0. The enzyme was distinguished from ALP (i.e., Alkaline phosphatase) by such tests as adding L-phenylalanine and heat treatment. Our measurement results of Ca2+-ATPase activity (mumoles Pi/mg protein/30 min) in human placental chorion were 21.9 +/- 2.4 (Mean +/- S.D.) at 10-15 gestational weeks, 19.1 +/- 1.4 at 16-27 gestational weeks, 31.4 +/- 7.2 at 28-35 gestational weeks, and at 36-42 gestational weeks, the AFD group showed 25.8 +/- 4.6, the LFD group, 27.9 +/- 2.1, and the SFD group, 21.2 +/- 1.9. Those of Na+ + K+-ATPase activity (mumoles Pi/mg protein/30 min) were 0.98 +/- 0.05 at 10-15 gestational weeks, 0.82 +/- 0.02 at 16-27 gestational weeks, 1.85 +/- 0.42 at 28-35 gestational weeks and at 36-42 gestational weeks, the AFD group showed 1.58 +/- 0.45, the LFD group, 1.49 +/- 0.37, and the SFD group, 1.68 +/- 0.36. As a result, Ca2+-ATPase activity tended to be higher at 28-35 gestational weeks than for other periods, while it showed lower for the SFD group than for the AFD group. As regards to Na+ + K+-ATPase activity, there were not seen any significant differences between the AFD placenta and the LFD placenta as compared with the AFD placenta.

Calcium transport in the lens

Evidence based on the following three observations suggests the existence of a calcium transport system in the mammalian lens: calcium levels in the lens are lower than that measured in the aqueous humor; calcium efflux is temperature-dependent and is reduced by inhibitors of Ca++ transport; and there exists a calcium-acivated, magnesium-dependent ATPase. In rat, bovine, dog, and rabbit lenses, the concentration of total calcium was found to be approximately 0.2 mM, at least an order of magnitude lower than that found in the aqueous humor. To determine the nature of the mechanism responsible for maintaining these low levels, calcium fluxes were measured. During the initial rapid phase of 45Ca efflux, the rate at 4 degrees C was reduced by 85% compared with that found at 37 degrees C. Efflux was not altered in the absence of external Na+. Calcium efflux was reduced, however, by lanthanum and propranolol, inhibitors of Ca/Mg ATPase. The presence of Ca/Mg ATPase was also demonstrated in the rat, bovine, and rabbit lens and was likewise inhibited by both lanthum and propranolol.

Plasma membrane of Entamoeba histolytica

Axenically propagated Entamoeba histolytica (HK9:NIH strain) were employed as starting material for the isoation of plasma membrane by a novel procedure. In the absence of known enzymatic markers, the externally disposed polypeptides of intact amoebae were iodinated and the incorporated label used to monitor membrane separation and recovery. 12 major plasma membrane polypeptides (12 x 10(3)-200 x 10(3) mol wt) were labeled and separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Each of these was a glycoprotein. Preincubation of amoebae with concanavalin A stabilized the plasma membranes as large sheets, facilitating its separation by low-speed centrifugation. Dissociation of the lectin with alpha-methyl mannoside, followed by additional homogenization led to vesiculation and further purification. The isolated plasma membrane was recovered in high yield (28%) and enriched 30-fold in terms of incorporated iodide. All iodinated surface glycoproteins of the intact organism were present in the plasma membrane fraction. A Ca++-dependent ATPase was enriched in the plasma membrane to a similar extent, but over one-half of the total activity was associated with internal, unlabeled membranes, suggesting a dual localization of this activity. The isolated plasma membrane was enriched in cholesterol and had a cholesterol:molar ratio of 0.87. It also contained larger amounts of an unusual phospholipid--ceramide aminoethyl phosphonate--a phospholipase-resistant species.

Difference infrared spectroscopy of aqueous model and biological membranes using an infrared data station

A Perkin-Elmer infrared Data Station associated with a simple IR spectrometer (model 298) is shown to give excellent results with aqueous model and biomembrane systems. Examples are presented of difference spectra obtained with lipid--water systems, reconstituted lipid--protein systems and a natural biomembrane. The spectra of the lipid after water subtraction and of the intrinsic protein after lipid subtraction from a model reconstituted Ca2+-ATPase membrane system are shown. The potential for studying intrinsic protein conformations is emphasised.

Histochemical demonstration of myosin Ca2+-ATPase accumulation in primary cultures of skeletal and heart muscle cells

A modified histochemical technique is described for the improved detection of myosin Ca2+-ATPase activity in single muscle cells in culture. The method was used to demonstrate the increase in myosin Ca2+-ATPase activity in differentiating chick skeletal muscle cells. Functional muscle cells were also positively identified in the heterogeneous cell population of primary hamster heart cell cultures. An age-dependent increase in the number of cells with high levels of myosin ATPase activity in mitotically arrested heart cell cultures was shown. Maturation of individual muscle cells could thus be evaluated.

Reliability and specificity of membrane adenosine triphosphatase localizations

The main development in ATPase cytochemistry in recent years is the development of three methodologically independent approaches to the localization of Na+, K+-ATPase. These methods in general support one another well and have led to significant insights into the mechanisms of bulk cation transport at several important sites. The area most in need of development is now the problem of specific localization of divalent ion-dependent ATPases at the plasma membrane. The value of the traditional Wachstein-Meisel methods appears to be very limited, and progress will depend on the introduction of more specific techniques.

(Ca2++Mg2+)-ATPase activity of sickle cell membranes: decreased activation by red blood cell cytoplasmic activator

Human red blood cells (RBCs) contain a cytoplasmic protein that activates membrane-bound (Ca2+ + Mg2+)-ATPase and the transport of Ca2+. The (Ca2+ + Mg2+)-ATPase of sickle cells showed a less than normal response to this activator. This was true whether the activator was obtained from normal or sickle cells. Activator present in sickle cell hemolysates fully activated the (Ca2+ + Mg2+)-ATPase of normal RBC membranes. These results demonstrate that membranes of sickle cells are defective in their response to the activator. Neither the apparent affinity for calcium nor the apparent affinity for activator was different comparing the (Ca2+ + Mg2+)-ATPase of sickle and normal membranes. Young, mature, and irreversibly sickled cells were separated by density gradient centrifugation, and membranes were prepared from each of these cell populations. No significant differences in ATPase activities were found based on cell age (density). The (Ca2+ + Mg2+)-ATPase of all populations of sickle cells showed a decreased response to the activator. Thus, it appears unlikely that the decreased response of the (Ca2+ + Mg2+)-ATPase of sickle cells is due to membrane damage caused by repeated sickling during the life-span of the cell. Reduced activation of (Ca2+ + Mg2+)-ATPase by the cytoplasmic activator may account for calcium accumulation in sickle cells.

Multilayer planar membranes of sarcoplasmic reticulum

Multilayer planar membranes were constructed between a pair of cellulose sheets from fragmented sarcoplasmic reticulum (FSR) as well as a mixture of egg yolk lecithin and the Ca2+-ATPase purified from FSR. Since sodium deoxycholate was used instead of organic solvents in order to dissolve phospholipids in the process of the membrane preparation, the total activity of the Ca2+-ATPase was still preserved in the planar membrane of FSR. It was also indicated using a spin label technique that the orientation of phospholipids in the planar membrane of FSR was considerably disturbed by the presence of proteins such as the Ca2+-ATPase included in FSR.

[Temperature-dependent changes in the profile of the sarcoplasmic reticulum membrane hydrophobic zones]

The dependence of the state of the hydrophobic zone of rabbit sarcoplasmic reticulum (SR) membranes on temperature of the membrane fragment suspension before rapid freezing was studied by the freeze fracturing technique. It was shown that within the temperature range of--15-- +37 degrees C the amount of intramembrane particles and their distribution in the membrane plane and between their convex and concave surfaces do not practically depend on the temperature of the SR membrane suspension. This is indicative of the lack of correlation between the physical state of the phospholipid matrix (gel -- liquid crystal) before freezing and the nature of the profile of the membrane hydrophobic zone revealed after fracturing. The disturbances in the protein -- lipid interactions in the membrane under the effects of mersalyl or aqueous solutions of diethyl ester followed by complete inactivation of Ca2+-dependent ATPase lead to a decrease in the amount of intramembrane particles, which is especially well-pronounced at 37 degrees and -15 degrees C.

Troponin C-like protein in chicken gizzard muscle

1. A troponin C-like protein was prepared from frozen chicken gizzard by preparative polyacrylamide gel electrophoresis and its apparent molecular weight was estimated to be about 15,500 daltons. 2. In urea gel electrophoresis, the mobility of the troponin C-like protein increased slightly in the presence of Ca2+, like that of skeletal muscle troponin C. On the other hand, the mobility of the the troponin C-like protein in glycerol gel electrophoresis, unlike that of skeletal muscle troponin C, was significantly decreased by Ca2+. 3. In alkaline gel electrophoresis, the troponin C-like protein formed a Ca2+-dependent complex with troponin I or troponin T from skeletal muscle. 4. The troponin C-like protein could neutralize the inhibitory effect of skeletal muscle troponin I on the Mg2+-activated ATPase of actomyosin from rabbit skeletal muscle, but could not confer Ca2+-sensitivity on the actomyosin in the presence of troponin I and troponin T from skeletal muscle.