Plasma membrane vesicles prepared from unadhered monocytes: Characterization of calcium transport and the calcium ATPase

We have purified unadhered human monocytes in sufficient quantities to prepare monocyte plasma membrane vesicles and study vesicular calcium transport. Monocytes were isolated from plateletpheresis residues by counterflow centrifugal elutriation. By combining this source and procedure, 7 x 10(8) monocytes of over 90% purity were obtained. The membranes, isolated on a sucrose step gradient, had an 18-fold enrichment in Na,K-ATPase, a 29-fold diminution of succinate dehydrogenase activity and were vesicular on transmission electron micrographs. The membrane vesicles loaded with oxalate accumulated calcium only in the presence of Mg and ATP. Calcium uptake did not occur if ATP was replaced by any of five nucleotide phosphates or if Mg was omitted. Calcium transport had a maximal velocity of 4 pmoles calcium/micrograms vesicle protein/min and a Km for calcium of 0.53 microM. The ionophore A23187 completely inhibited calcium accumulation while 5 mM sodium cyanide and 10 microM ouabain had no effect. A calcium-activated ATPase was present in the same plasma membrane vesicles. The calcium ATPase had a maximal velocity of 18.0 pmoles calcium/micrograms vesicle protein/min and a Km for calcium of 0.60 microM. Calcium-activated ATPase activity was absent if Mg was omitted or if (gamma - 32P) GTP replaced (gamma - 32P) ATP. Monocyte plasma membranes that were stripped of endogenous calmodulin by EGTA treatment showed a reduced level of calcium uptake and calcium ATPase activity. The addition of exogenous calmodulin restored the transport activity to that of unstripped monocyte plasma membranes. Thus, monocyte plasma membrane vesicles contain a highly specific, ATP-dependent calcium transport system and a calcium-ATPase with similar high calcium affinities.     

Human ABCA3, a product of a responsible gene for abca3 for fatal surfactant deficiency in newborns, exhibits unique ATP hydrolysis activity and generates intracellular multilamellar vesicles

ABCA3 is highly expressed at the membrane of lamellar bodies in alveolar type II cells, in which pulmonary surfactant is stored. ABCA3 gene mutations cause fatal surfactant deficiency in newborns. We established HEK293 cells stably expressing human ABCA3 and analyzed the function. Exogenously expressed ABCA3 is glycosylated and localized at the intracellular vesicle membrane. ABCA3 is efficiently photoaffinity labeled by 8-azido-[alpha(32)P]ATP, but not by 8-azido-[gamma(32)P]ATP, when the membrane fraction is incubated in the presence of orthovanadate. Photoaffinity labeling of ABCA3 shows unique metal ion-dependence and is largely reduced by membrane pretreatment with 5% methyl-beta-cyclodextrin, which depletes cholesterol. Electron micrographs show that HEK293/hABCA3 cells contain multivesicular, lamellar body-like structures, which do not exist in HEK293 host cells. Some fuzzy components such as lipids accumulate in the vesicles. These results suggest that ABCA3 shows ATPase activity, which is induced by lipids, and may be involved in the biogenesis of lamellar body-like structures.     

Subcellular Localization of Simian Virus 40 Large Tumor Antigen

The distribution of simian virus 40 large tumor antigen in subcellular fractions from simian virus 40-transformed hamster (H-50) and mouse (VLM) cells and from simian virus 40-infected monkey cells was determined. Solubilized [(35)S]-methionine- or (32)P(i)-labeled surface membrane and nuclear fractions were prepared, immunoprecipitated with hamster anti-T serum, and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Tumor antigen with an apparent molecular weight of approximately 96,000 was detected in both subcellular fractions. Minor components of approximately 68,000 and approximately 56,000 with anti-T reactivity which labeled with [(35)S]methionine were also detected in both fractions from H-50 cells, as were components of approximately 140,000 and approximately 56,000 from VLM cells. The 56,000 component appeared to be greatly reduced in (32)P(i)-labeled surface membrane fractions. Normal cells or cells transformed with a heterologous agent, such as polyoma virus or a chemical carcinogen, lacked immunoprecipitable tumor antigen. Cell fractionation was monitored by [(3)H]thymidine labeling, NADH-diaphorase activity, and Na(+)-K(+)-dependent ATPase activity. These analyses revealed only trace contamination of surface membranes by nuclei, extremely low levels of nuclear rupture during homogenization, and an approximate 10-fold enrichment of surface membrane. Reconstruction experiments demonstrated that soluble tumor antigen failed to associate or copurify with surface membranes during fractionation procedures. These results indicate the presence of a protein in the plasma membrane of cells transformed or infected by simian virus 40 that is immunologically indistinguishable from nuclear tumor antigen.     

Anion dependence of Ca2+ transport and (Ca2+ + K+)-stimulated Mg2+-dependent transport ATPase in rat pancreatic endoplasmic reticulum

Anion dependence of (Ca2+ + K+)-stimulated Mg2+-dependent transport ATPase and its phosphorylated intermediate have been characterized in both "intact" and "broken" vesicles from endoplasmic reticulum of rat pancreatic acinar cells using adenosine 5'-[gamma-32P] triphosphate ([gamma-32P]ATP). In intact vesicles (Ca2+ + K+)-Mg2+-ATPase activity was higher in the presence of Cl- or Br- as compared to NO3-, SCN-, cyclamate-, SO4(2-) or SO3(2-). Incorporation of 32P from [gamma-32P]ATP into the 100-kDa intermediate of this Ca2+ATPase was also higher in the presence of Cl-, Br-, NO3- or SCN- as compared to cyclamate-, SO4(2-) or SO3(2-). When the membrane permeability barrier to anions was abolished by breaking vesicle membrane with the detergent Triton X-100 (0.015%) (Ca2+ + K+)-Mg2+ATPase activity in the presence of weakly permeant anions, such as SO4(2-) and cyclamate-, increased to the level obtained with Cl-. However, 32P incorporation into 100-kDa protein was still higher in the presence of Cl- as compared to cyclamate-, indicating a direct effect of Cl- on the Ca2+ATPase molecule. The anion transport blocker 4,4-diisothiocyanostilbene-2,2-disulfonate (DIDS) inhibited (Ca2+ + K+)-Mg2+ATPase activity to about 10% of the Cl- stimulation level, irrespective of the sort of anions present in both intact and broken vesicles. This indicates a direct effect of DIDS on (Ca2+ + K+)-Mg2+ATPase. K+ ionophore valinomycin influenced (Ca2+ + K+)-Mg2+ATPase activity according to the actual K+ gradient: Ko+ greater than Ki+ caused inhibition, Ko+ less than Ki+ caused stimulation. From these results we conclude that Ca2+ transport into endoplasmic reticulum is coupled to ion movements which must occur to maintain electroneutrality.     

Effect of parathyroid hormone on Na+-dependent phosphate transport and cAMP-dependent 32P phosphorylation in brush border vesicles from isolated perfused canine kidneys

Concentrative uptake of 32Pi induced by the dissipation of a Na+ gradient (overshoot) was demonstrated in brush border membrane vesicles obtained from isolated perfused canine kidneys. Na+-dependent 32Pi transport was decreased in brush border vesicles from isolated kidneys perfused with parathyroid hormone (PTH) for 2 h compared to uptake measured in vesicles from kidneys perfused without PTH. Cyclic AMP-dependent 32P phosphorylation of a 62,000 Mr protein band was demonstrable on autoradiograms of sodium dodecyl sulfate-polyacrylamide gels of membrane suspensions from kidneys perfused +/- PTH. Evidence that perfusion with PTH resulted in cAMP-dependent phosphorylation in isolated kidneys from parathyroidectomized dogs (decreased cAMP-dependent 32P phosphorylation of the 62,000-Mr band in brush border vesicles) was obtained after 2-h perfusion with PTH. Decreased 32P phosphorylation was not observed if membranes were allowed to dephosphorylate prior to 32P phosphorylation in vitro. We conclude that brush border vesicles from isolated perfused canine kidneys can be used to study the action of PTH on Na+-Pi cotransport in brush border membranes and on cAMP-dependent phosphorylation of the membrane. It is strongly suggested that PTH effects changes in Na+-dependent 32Pi transport in isolated brush border vesicles and changes in 32P phosphorylation of vesicles via a direct action on the renal cortical cell rather than as a consequence of extrarenal actions of the hormone.     

Calcium Transport in Sealed Vesicles from Red Beet (Beta vulgaris L.) Storage Tissue : I. Characterization of a Ca-Pumping ATPase Associated with the Endoplasmic Reticulum

Calcium transport was examined in microsomal membrane vesicles from red beet (Beta vulgaris L.) storage tissue using chlorotetracycline as a fluorescent probe. This probe demonstrates an increase in fluorescence corresponding to calcium accumulation within the vesicles which can be collapsed by the addition of the calcium ionophore A23187. Calcium uptake in the microsomal vesicles was ATP dependent and completely inhibited by orthovanadate. Centrifugation of the microsomal membrane fraction on a linear 15 to 45% (w/w) sucrose density gradient revealed the presence of a single peak of calcium uptake which comigrated with the marker for endoplasmic reticulum. The calcium transport system associated with endoplasmic reticulum vesicles was then further characterized in fractions produced by centrifugation on discontinous sucrose density gradients. Calcium transport was insensitive to carbonylcyanide m-chlorophenylhydrazone indicating the presence of a primary transport system directly linked to ATP utilization. The endoplasmic reticulum vesicles contained an ATPase activity that was calcium dependent and further stimulated by A23187 (Ca(2+), A23187 stimulated-ATPase). Both calcium uptake and Ca(2+), A23187 stimulated ATPase demonstrated similar properties with respect to pH optimum, inhibitor sensitivity, substrate specificity, and substrate kinetics. Treatment of the red beet endoplasmic reticulum vesicles with [gamma-(32)P]-ATP over short time intervals revealed the presence of a rapidly turning over 96 kilodalton radioactive peptide possibly representing a phosphorylated intermediate of this endoplasmic reticulum associated ATPase. It is proposed that this ATPase activity may represent the enzymic machinery responsible for mediating primary calcium transport in the endoplasmic reticulum linked to ATP utilization.     

Effects of vanadate on the rotational dynamics of spin-labeled calcium adenosinetriphosphatase in sarcoplasmic reticulum membranes

We have studied the effects of vanadate on the rotational motion of the calcium adenosine-triphosphatase (Ca-ATPase) from sarcoplasmic reticulum (SR), using saturation-transfer electron paramagnetic resonance (ST-EPR). Vanadate has been proposed to act as a phosphate analogue and produce a stable intermediate state similar to the phosphoenzyme. This study provides evidence about the physical state of this intermediate. In particular, since ST-EPR provides a sensitive measure of microsecond protein rotational mobility, and hence of protein-protein association, these studies allowed us to ask (a) whether the vanadate-induced protein association observed in electron micrographs of SR vesicles also occurs under physiological (as opposed to fixed, stained, or frozen) conditions and (b) whether vanadate-induced changes in protein association also occur under conditions sufficient for enzyme inhibition but not for the production of large arrays detectable by electron microscopy (EM). At 5 mM decavanadate, a concentration sufficient to crystallize the ATPase on greater than 90% of the membrane surface area in EM, ST-EPR showed substantial immobilization of the spin-labeled protein, indicating protein-protein association in the unstained vesicles. Conventional EPR spectra of lipid probes showed that lipid hydrocarbon chain mobility is unaffected by decavanadate-induced protein crystallization in SR, suggesting that changes in protein-protein contacts do not involve the lipid hydrocarbon region. At 5 mM monovanadate, a concentration sufficient to inhibit the ATPase but not to form crystals detectable by EM, no changes were observed in ST-EPR or conventional EPR spectra of either protein or lipid.(ABSTRACT TRUNCATED AT 250 WORDS)     

Identification of 3-O-(4-benzoyl)benzoyladenosine 5'-triphosphate- and N,N'-dicyclohexylcarbodiimide-binding subunits of a higher plant H+-translocating tonoplast ATPase

The polypeptide composition of the NO-3-sensitive H+-ATPase of vacuolar membrane (tonoplast) vesicles isolated from red beet (Beta vulgaris L.) storage root was investigated by affinity labeling with [alpha-32P]3-O-(4-benzoyl)benzoyladenosine 5'-triphosphate [( alpha-32P]BzATP) and [14C]N,N'-dicyclohexylcarbodiimide [( 14C]DCCD). The photoactive affinity analog of ATP, BzATP, is a potent inhibitor of the tonoplast ATPase (apparent KI = 11 microM) and the photolysis of [alpha-32P]BzATP in the presence of native tonoplast yields one major 32P-labeled polypeptide of 57 kDa. Photoincorporation into the 57-kDa polypeptide shows saturation with respect to [alpha-32P]BzATP concentration and is blocked by ATP. [14C]DCCD, a hydrophobic carboxyl reagent and potent irreversible inhibitor of the tonoplast ATPase (k50 = 20 microM) labels a 16-kDa polypeptide in native tonoplast. The tonoplast ATPase is purified approximately 12-fold by Triton X-100 solubilization and Sepharose 4B chromatography. Partial purification results in the enrichment of two prominent polypeptides of 67 and 57 kDa. Solubilization, chromatography, and sodium dodecylsulfate-polyacrylamide gel electrophoresis of tonoplast labeled with [alpha-32P]BzATP or [14C]DCCD results in co-purification of the 57- and 16-kDa labeled polypeptides with ATPase activity. It is concluded that the tonoplast H+-ATPase is a multimer containing structurally distinct BzATP- and DCCD-binding subunits of 57 and 16 kDa, respectively. The data also suggest the association of a 67-kDA polypeptide with the ATPase.     

Adenosine triphosphate-linked concentration of calcium ions in a particulate fraction of rabbit muscle

ATPase and ATP-dependent calcium ion concentration was studied with a membrane fraction isolated from homogenized rabbit skeletal muscle by differential centrifugation. Electron micrographs of the fraction indicate that it consists mainly of resealed tubules and vesicles of the endoplasmic reticulum. The up-to-1400-fold concentration of calcium in this fraction might be explained by proposing the existence of an energy-requiring system for the transport of calcium ions into the tubules or vesicles.     

Gel electrophoretic and density gradient analysis of the (K + Ca)-ATPase and the (Na + K)-ATPase activities of cardiac membrane vesicles

The two major ATPase activities of intact and leaky cardiac membrane vesicles (microsomes) were characterized with respect to ionic activation requirements. The predominant ATPase activity of intact vesicles was (K⁺ + Ca²⁺)-ATPase, an enzymic activity localized to sarcoplasmic reticulum, whereas the predominant ATPase activity of leaky, sodium dodecyl sulfate-pretreated vesicles was (Na⁺ + K⁺)-ATPase, an enzymic activity localized to sarcolemma. The (K⁺ + Ca²⁺)-ATPase activity was stimulated 4- to 5-fold by 100 mM K⁺ in the presence of 50 μM Ca²⁺. Phosphorylation of the (K⁺ + Ca²⁺)-ATPase of intact vesicles with [γ-³²P]ATP was Ca²⁺ dependent, and monovalent cations including K⁺ increased the level of [³²P]phosphoprotein by up to 50% when phosphorylation was measured at 5°C. After the intact vesicles were treated with SDS (0.30 mg/ml), (K⁺ + Ca²⁺)-ATPase was inactivated, as was Ca²⁺-dependent ³²P incorporation. The monovalent cation-stimulated ATPase activity of the particulate residue (SDS-extracted membrane vesicles) displayed the usual characteristics of ouabain-sensitive (Na⁺ + K⁺)-ATPase and the activity was increased 9- to 14-fold over the small amount of patent (Na⁺ + K⁺)-ATPase activity of intact membrane vesicles. ³²P incorporation by the (Na⁺ + K⁺)-ATPase of SDS-extracted vesicles was Na⁺ dependent, and Na⁺-stimulated incorporation was increased 7- to 9-fold over that of intact vesicles.Slab gel polyacrylamide electrophoresis of both intact and SDS-extracted crude vesicle preparations revealed at least 40 distinct Coomassie Blue-positive protein bands and provided evidence for a possible heterogeneous membrane origin of the vesicles. Periodic acid-Schiff staining of the gels revealed at least two major glycoproteins. Simultaneous electrophoresis of the ³²P-intermediates of the (K⁺ + Ca²⁺)-ATPase and the (Na⁺ + K⁺)-ATPase in the same gels did not resolve the two enzymes clearly. With sucrose gradient centrifugation of intact membrane vesicles, it was possible to physically resolve the two ATPase activities. Latent (Na⁺ + K⁺)-ATPase activity (unmasked by exposing the various fractions to SDS) was found in the higher regions of the gradient, whereas (K⁺ + Ca²⁺)-ATPase activity was primarily in the denser regions. A reasonable interpretation of the data is that cardiac microsomes consist of membrane vesicles derived both from sarcolemma and sarcoplasmic reticulum. (Na⁺ + K⁺)-ATPase is localized to intact vesicles of sarcolemma but is mainly latent, whereas (K⁺ + Ca²⁺)-ATPase is mostly patent and is localized to vesicles of sarcoplasmic reticulum.     

ATP synthesis at 100 degrees C by an ATPase purified from the hyperthermophilic archaeon Pyrodictium abyssi

The chemolithoautotrophic archaeon Pyrodictium abyssi isolate TAG 11 lives close to 100 degrees C and gains energy by sulfur respiration, with hydrogen as electron donor. From the membranes of this hyperthermophile, an ATPase complex was isolated. The purified enzyme consists of six major polypeptides, the 67, 51, 41, 26 and 22 kDa subunits composing the AF(1) headpiece, and the 7 kDa proteolipid of the AF(0) component. The headpiece of the enzyme restored the formation of ATP during sulfur respiration in membrane vesicles from which it had been removed by low salt treatment. Characteristics of the reconstituted activity suggest that the same enzyme is responsible for ATP formation in untreated membranes. ATP formation was neither sensitive to ionophores and uncouplers, nor to dicyclohexyl carbodiimide, but depended on closed vesicles. Both ATPase activity (up to 2 micromol per min and mg protein) as well as ATP formation (up to 0.4 micromol per min and mg membrane protein) were highest at 100 degrees C. A P/e2 ratio of close to one can be estimated for sulfur respiration with hydrogen. In addition to ATP, autoradiographic detection revealed the formation of high quantities of (33)P(i)-labeled ADP and of another compound not identified so far.     

Sidedness of ceramide-phosphoethanolamine synthesis on rat liver plasma membrane

Phosphatidylethanolamine:ceramide-ethanolaminephosphotransferase catalyzes the synthesis of ceramide-ethanolamine, a sphingomyelin analogue. Its transverse localization in rat liver plasma membrane was studied by treating intact and deoxycholate- or Triton X-100-disrupted membrane vesicles with trypsin or bacterial protease. The latency of ATPase was preserved during protease treatment; its value was 80% in the membrane vesicles obtained by sucrose gradient procedure alone and 91.2% in the vesicles isolated after sucrose gradient plus two-phase partitioning. This suggested that membrane integrity was not altered and that 90% of the vesicles were right-side out. When the sucrose gradient was followed by the two-phase procedure, 62% of phosphatidylethanolamine:ceramide-ethanolamine-phosphotransferase was accessible to the protease action, but only 45% in vesicles obtained by sucrose gradient alone. Our results suggest that at least a sizable portion of the active center of the enzyme responsible of biosynthesis of ceramide-phosphoethanolamine is located on the external side of liver plasma membrane and that the other is embedded in the membrane interior and is not accessible to trypsin, even in the presence of detergent.     

Demonstration of two forms of calcium pumps by thapsigargin inhibition and radioimmunoblotting in platelet membrane vesicles

In mixed membrane vesicles prepared from human platelets, the presence of two distinct calcium pump enzymes (molecular mass 100 and 97 kDa) was demonstrated by 32P autoradiography, immunoblotting, and thapsigargin inhibition. Both the 100- and 97-kDa membrane proteins showed calcium-dependent phosphoenzyme formation and reacted with a polyclonal anti-sarcoplasmic reticulum calcium pump antiserum, while only the 100-kDa protein reacted with the antiserum specific for the sarco-endoplasmic reticulum-type calcium transport ATPase 2b isoform. Thapsigargin, inhibiting active calcium transport in platelet membrane vesicles, predominantly blocked the phosphoenzyme formation of the 100-kDa isoform and of the tryptic calcium pump fragments of 55 and 35 kDa, while lanthanum specifically increased the phosphoenzyme formation of the 97-kDa enzyme and of the tryptic fragment of 80 kDa. These results indicate the presence of the sarco-endoplasmic reticulum-type calcium transport ATPase 2b isoform and of a yet unidentified, 97-kDa calcium pump protein in human platelet membranes.     

ADENOSINE TRIPHOSPHATE-LINKED CONCENTRATION OF CALCIUM IONS IN A PARTICULATE FRACTION OF RABBIT MUSCLE

ATPase and ATP-dependent calcium ion concentration was studied with a membrane fraction isolated from homogenized rabbit skeletal muscle by differential centrifugation. Electron micrographs of the fraction indicate that it consists mainly of resealed tubules and vesicles of the endoplasmic reticulum. The up-to-1400-fold concentration of calcium in this fraction might be explained by proposing the existence of an energy-requiring system for the transport of calcium ions into the tubules or vesicles.     

Stimulation of ATPase activity in barley (Hordeum vulgare) root plasma membrane after treatment of intact tissues and cell free extracts with triacontanol

Ca²⁺- and Mg²⁺-dependent ATPase activity (EC 3.6.1.3) in a plasma membrane-enriched fraction increased rapidly after in vivo application of physiologically active concentrations of triacontanol (TRIA) to the roots of barley ( Hordeum vulgare L. cv. Conquest) seedlings. Ca²⁺- and Mg²⁺-dependent ATPase activity was 64 and 85% higher, respectively, in the roots of seedlings germinated in the presence of growth-promoting concentrations of TRIA compared to controls. The increase in vivo was concentration dependent, with the greatest increase obtained at 2.3 n M TRIA. Maximal stimulation of ATPase activity of excised tissue treated with TRIA coincided with the temperature at which the barley was grown. At this temperature the plasma membrane is primarily in a mixed gel/liquid crystalline state. Pretreatment of barley roots with cyclohexamide did not alter ATPase stimulation by TRIA. Two to three times more [¹⁴C]-TRIA (mg membrane protein)⁻¹ was found associated with plasma membrane-enriched vesicles treated with TRIA than with vesicles enriched for mitochondrial membranes or for vesicles enriched for tonoplast, Golgi and rough endoplasmic reticulum. Both Ca²⁺- and Mg²⁺-dependent ATPase activity increased by 40–60% within 30 min of the addition of 2.3 n M TRIA to cell-free extracts of barley roots. The addition of octacosanol, the C₂₈ analogue of TRIA, to cell-free extracts did not affect metal-dependent ATPase activity. Consistent with many studies in the green-house, simultaneous additions of equimolar amounts of TRIA and octacosanol to cell-free extracts resulted in inhibition of ATPase stimulation by TRIA. TRIA may directly affect plasma membrane function in barley roots.     

Local Anesthetics Inhibit the Ca2+,Mg2+-ATPase Activity of Rat Brain Synaptosomes

Many biochemical effects of local anesthetics are expressed in Ca2+-dependent processes [Volpi M., Sha'afi R.I., Epstein P.M., Andrenyak P.M., and Feinstein M.B. (1981) Proc. Natl. Acad. Sci. USA 78, 795-799]. In this communication we report that local anesthetics (dibucaine, tetracaine, lidocaine, and procaine and the analogue quinacrine) inhibit the Ca2+-dependent and the Mg2+-dependent ATPase activity of rat brain synaptosomes and of membrane vesicles derived from them by osmotic shock. This inhibition is induced by concentrations of these drugs close to their pharmacological doses, and a good correlation between K0.5 of inhibition and their relative anesthetic potency is found. The Ca2+-dependent ATPase is more selectively inhibited at lower drug concentrations. The physiological relevance of these findings is discussed briefly.     

Orientation of membrane vesicles fromEscherichia coli prepared by different procedures

Summary The orientation of membrane vesicles prepared fromEscherichia coli by either French press, sonication or ethylenediamine tetraacetate (EDTA)-lysozyme was examined. The following procedures were used to determine orientation: (1) accessibility of the impermeable ferricyanide ion to the respiratory chain; (2) inhibition of membranal ATPase by specific antiserum; (3) binding of ATPase to the membrane. Data with spheroplasts indicated that ATPase, ATPase binding sites and ferricyanide reductase activities were localized on the inner part of the cytoplasmic membrane. Thus, there was no demonstrable NADH-ferricyanide reductase activity, low ATPase activity, no inhibition of ATPase by antiserum and no binding of purified ATPase by spheroplasts. In the case of membrane vesicles prepared by French press or sonication, the ATPase activity, the ATPase binding site and the site where ferricyanide takes electrons from the respiratory chain all appeared to be on the outside of the vesicles, suggesting that they are inverted. In the case of EDTA-lysozyme vesicles, which are widely used for transport studies, about half of the ATPase binding sites and ferricyanide reactive sites were exposed to the outside. Sixty percent of the ATPase activity was sensitive to antiserum. The two most probable explanations for these data are: (1) partial inversion of EDTA-lysozyme vesicles in the course of preparation; (2) movement of marker enzymes within the membrane vesicles during their isolation.     

The importance of carboxyl groups on the lumenal side of the membrane for the function of the Ca(2+)-ATPase of sarcoplasmic reticulum

The conventional model for transport of Ca(2+) by the Ca(2+)-ATPase of skeletal muscle sarcoplasmic reticulum (SR) involves a pair of binding sites for Ca(2+) that change upon phosphorylation of the ATPase from being high affinity and exposed to the cytoplasm to being low affinity and exposed to the lumen. However, a number of recent experiments suggest that in fact transport involves two separate pairs of binding sites for Ca(2+), one pair exposed to the cytoplasmic side and the other pair exposed to the lumenal side. Here we show that the carbodiimide 1-ethyl-3-[3-(dimethylamino)-propyl] carbodiimide (EDC) is membrane-impermeable, and we use EDC to distinguish between cytoplasmic and lumenal sites of reaction. Modification of the Ca(2+)-ATPase in sealed SR vesicles with EDC leads to loss of ATPase activity without modification of the pair of high affinity Ca(2+)-binding sites. Modification of the purified ATPase in unsealed membrane fragments was faster than modification in SR vesicles, suggesting the presence of more quickly reacting lumenal sites. This was confirmed in experiments measuring EDC modification of the ATPase reconstituted randomly into sealed lipid vesicles. Modification of sites on the lumenal face of the ATPase led to loss of the Ca(2+)-induced increase in phosphorylation by P(i). It is concluded that carboxyl groups on the lumenal side of the ATPase are involved in Ca(2+) binding to the lumenal side of the ATPase and that modification of these sites leads to loss of ATPase activity. The presence of MgATP or MgADP leads to faster inhibition of the ATPase by EDC in unsealed membrane fragments than in sealed vesicles, suggesting that binding of MgATP or MgADP to the ATPase leads to a conformational change on the lumenal side of the membrane.     

Normal serum cytotoxicity for P32-labeled smooth Enterobacteriaceae. II. Fate of macromolecular and lipid phosphorus of damaged cells

Spitznagel, John K. (University of North Carolina, Chapel Hill). Normal serum cytotoxicity for P(32)-labeled smooth Enterobacteriaceae. II. Fate of macromolecular and lipid phosphorus of damaged cells. J. Bacteriol. 91:148-152. 1966.-Fresh, normal adult guinea pig serum released micro- and macromolecular forms of metabolically incorporated P(32) from smooth Escherichia coli. A significant amount of P(32)-labeled phospholipid was also released. The overall acid solubility distribution of the P(32) label in bacterial suspensions was very little affected in fresh serum, although P(32)-labeled cytoplasmic contents and cell walls of E. coli lost some P(32) when they were suspended in fresh or heat-inactivated normal serum. These findings confirmed and extended earlier evidence that the peripheral wall and membrane structures of smooth E. coli are extensively damaged by factors in fresh normal serum.     

Identification of the phosphorylated intermediate of the Neurospora plasma membrane H+-ATPase as beta-aspartyl phosphate

The chemical nature of the phosphoryl enzyme linkage of the electrogenic proton-translocating ATPase (ATP phosphohydrolase, EC 3.6.1.3) in the plasma membrane of Neurospora has been identified as a mixed anhydride between phosphate and the beta-carboxyl group of an aspartic acid residue in the polypeptide chain. Incubation of isolated Neurospora plasma membrane vesicles containing 32P-labeled ATPase in buffers of increasing pH followed by analysis of the hydrolysis products yielded a pH versus hydrolysis profile characteristic of an acyl phosphate linkage. Reaction of labeled membranes with hydroxylamine at pH 5.3 also released [32P]i from the ATPase. Amino acid analyses of the Na[3H]BH4 reduction products obtained from membranes containing phosphorylated and dephosphorylated ATPase identified [3H]homoserine, the expected reduction product of beta-aspartyl phosphate, as the only additional tritiated reduction product in the samples from phosphorylated membranes. Tritium was not found in alpha-amino-delta-hydroxyvaleric acid, the reduction product of gamma-glutamyl phosphate, nor in proline, the degradation product of alpha-amino-delta-hydroxyvaleric acid. These results indicate that the phosphorylated intermediate of the Neurospora plasma membrane ATPase is a beta-aspartyl phosphate identical with that already known to exist in the Na+:K+- and Ca2+-translocating ATPases of animal cell origin. A common model for the mechanisms of all 3 ion-translocating ATPases is presented.