Studies on the surface and cytoplasmic membranes of Ehrlich ascites-carcinoma cells. I. The hydrolysis of ATP and related nucleotides by microsomal membranes

Comparative subcellular distribution of apyrase from animal and plant sources. Characterization of microsomal apyrase

1. Apyrase (ATP: diphosphohydrolase) has been found in the microsomal fraction of rat salivary gland, mammary gland and uterus. 2. This enzyme, already described in plant tissue, is mainly present as a soluble polypeptide in tubers of Solanum tuberosum. 3. A fraction of this enzyme is associated with the microsomal fraction with a higher specific activity than the soluble one, for either ATP or ADP as substrate. 4. Apyrase bound to microsomes from rat and potato tissues was characterized in its substrate specificity and effect of inhibitors. 5. The Km values for ATP and ADP, optimum pH and metal ion requirement were determined. 6. A characteristic common to the microsomal and soluble apyrases is the stimulatory effect of a potato activator protein of soluble plant apyrase. 7. The microsomal-bound apyrase from rat and potato tissues were solubilized and subjected to size-exclusion chromatography. 8. The mammary gland and salivary gland apyrases eluted as molecular aggregates, in contrast to the uterus and potato enzyme.

Rat liver plasma membrane Ca2+- or Mg2+-activated ATPase. Evidence for proton movement in reconstituted vesicles

The Ca2+- or Mg2+-activated ATPase from rat liver plasma membrane was partly purified by treatments with sodium cholate and lysophosphatidylcholine, and by isopycnic centrifugation on sucrose gradients. The ATPase activity had high sensitivity to detergents, poor nucleotide specificity and broad tolerance for divalent cations. It was insensitive to mitochondrial ATPase inhibitors such as oligomycin and to transport ATPase inhibitors such as vanadate and ouabain. Using the cholate dialysis procedure, the partly purified enzyme was incorporated into asolectin vesicles. Upon addition of Mg2+-ATP, fluorescence quenching of 9-amino-6-chloro-2-methoxyacridine (ACMA) was observed. The quenching was abolished by a protonophore, carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP). Asolectin vesicles or purified ATPase alone failed to promote quenching. These data suggest that the Ca2+- or Mg2+-activated ATPase from rat liver plasma membrane is able of H+-translocation coupled to ATP hydrolysis.

Cytochemical localization of 5'-nucleotidase in guinea-pig sympathetic ganglia

Cytochemical techniques were used to study the localization of 5'-nucleotidase in sympathetic ganglia of the guinea-pig. Enzymatic activity was revealed in plasma membranes. Both the neuronal and satellite cell membranes contained the enzyme. Most of the activity was seen in the membrane of the satellite cells and this was interpreted to indicate a high level of purine utilization by these cells. The neurons displayed enzymatic activity in the membranes of non-specialized neuronal boundaries as well as at synapses.

Characterization of the membrane bound Mg2+-ATPase of rat skeletal muscle

A procedure was developed to isolate a membrane fraction of rat skeletal muscle which contains a highly active Mg2+-ATPase (5-25 mumol Pi/mg min). The rate of ATP hydrolysis by the Mg2+-ATPase was nonlinear but decayed exponentially (first-order rate constant greater than or equal to 0.2 s-1 at 37 degrees C). The rapid decline in the ATPase activity depended on the presence of ATP or its nonhydrolyzable analog 5'-adenylyl imidodiphosphate (AdoPP[NH]P). Once inactivated, removal of ATP from the medium did not immediately restore the original activity. ATP- or AdoPP[NH]P-dependent inactivation could be blocked by concanavalin A, wheat germ agglutinin or rabbit antiserum against the membrane. Additions of these proteins after ATP addition prevented further inactivation but did not restore the original activity. Low concentrations of ionic and nonionic detergents increased the rate of ATP-dependent inactivation. Higher concentrations of detergents, which solubilize the membrane completely, inactivated the Mg2+-ATPase. Cross-linking the membrane components with glutaraldehyde prevented ATP-dependent inactivation and decreased the sensitivity of the Mg2+-ATPase to detergents. It is proposed that the regulation of the Mg2+-ATPase by ATP requires the mobility of proteins within the membrane. Cross-linking the membrane proteins with lectins, antiserum or glutaraldehyde prevents inactivation; increasing the mobility with detergents accelerates ATP-dependent inactivation.

The common occurrence of ATP diphosphohydrolase in mammalian plasma membranes

In the plasma membranes from several mammalian tissues (including normal and tumor tissues), a Mg2+ (or Ca2+)-dependent ATP phosphohydrolase activity is present in much greater amount than the (Na+ + K+)-ATPase. The ouabain-insensitive activity can be attributed to at least two enzymes, an ATPase (EC 3.6.1.3) and an ATP diphosphohydrolase (EC 3.6.1.5). The ATPase hydrolyzes ATP and other nucleoside triphosphates and is not inhibited by azide. The ATP diphosphohydrolase hydrolyzes both ATP and ADP (and other nucleoside tri- and diphosphates) and the hydrolysis of adenine nucleotides is strongly inhibited by 10 mM azide. The ratios of these two enzymes in the various membranes (as determined by the extent of azide inhibition) vary widely. The ATP diphosphohydrolase accounts for most of the Mg2+ (or Ca2+)-dependent ATP hydrolysis activity of the plasma membranes of liver (mouse), kidney (dog), two mouse sarcomas, and a human astrocytoma (xenograft in athymic mice). The ATPase is more dominant in the plasma membranes from mouse brain and human oat cell carcinoma. The widespread presence of the ATP diphosphohydrolase in plasma membrane from various types of tissues is demonstrated for the first time and is of particular interest in view of its relatively high activity in the plasma membranes of two sarcomas. The membrane-bound ATP diphosphohydrolase is characterized with respect to its metal ion activators, substrates, and inhibitors. These results should facilitate the distinction of this enzyme from other ATP hydrolyzing enzymes of plasma membranes in future investigations.

The determination and localization of sialic acid in guinea-pig granulocytes

When intact guinea-pig granulocytes (polymorphonuclear leucocytes) disrupted by sonication or with detergent were treated with neuraminidase from Vibrio cholerae, 3.1--3.2 nmol of sialic acid/10(7) cells was released. By using a chromatographic procedure for the specific determination of total cell sialic acid, this releasable portion was found to constitute 70% of the total sialate. All of the neuraminidase-releasable sialic acid of the cells could be removed by enzymic treatment of intact cells with neuraminidase. It thus seemed likely that the neuraminidase-releasable sialic acid is all on the cell surface. To make sure that the result was not due to entry of neuraminidase into the cells, the enzyme was bound covalently to Sepharose 6B, and intact polymorphonuclear leucocytes were treated with the bound enzyme. All of the neuraminidase-releasable sialic acid could still be removed, though more slowly. The cells remained intact and only 1.5--2% of the bound enzyme was released from the Sepharose during incubation. Freed enzyme could have been responsible, at the very most, for release of 18% of the sialic acid. Fractionation studies showed that the nucleus and cytoplasm contain low amounts of sialic acid and that the neuraminidase-releasable sialic acid distributes in a manner similar to the distribution of 5'-nucleotidase, an unambiguous marker for the plasma membrane in these cells. Thus neuraminidase-releasable sialate constitutes a clear marker for the membrane of polymorphonuclear leucocytes. Most of the neuraminidase-insensitive sialate was present in the granule fraction. Removal of sialic acid from intact polymorphonuclear leucocytes did not affect their ecto-AMPase, -ATPase and -p-nitrophenyl phosphatase activities.

Neutrophil plasma membranes. I. High-yield purification of human neutrophil plasma membrane vesicles by nitrogen cavitation and differential centrifugation

Neutrophil chemotaxis, phagocytosis, and oxygen-dependent microbicidal activity are initiated by interactions of stimuli with the plasma membrane. However, difficulties in neutrophil plasma membrane isolation have precluded studies on the precise structure or function of this cellular component. In this paper, a method is described for the isolation of representative human neutrophil plasma membrane vesicles, using nitrogen cavitation for cell disruption and a combination of differential centrifugation and equilibrium ultracentrifugation in Dextran gradients for membrane fractionation. Multiple biochemical markers and galactose oxidase-tritiated sodium borohydride surface labeling were employed to follow the yield, purity, and distribution of plasma membranes, nuclei, lysosomes, endoplasmic reticulum, mitochondria, and cytosol. According to these markers, neutrophil plasma membranes were exposed to minimal lysosomal hydrolytic enzymes and could be isolated free of other subcellular organelles. In contrast, disruption of neutrophils by mechanical homogenization resulted in > 20% lysosomal rupture and significant plasma membrane proteolysis. Electron microscopy demonstrated that plasma membranes isolated after nitrogen cavitation appeared to be sealed vesicles with striking homogeneity.

Modification of the immunologic properties of the cell surface

Living CF1 mouse-transplantable spontaneous mammary adenocarcinoma cells were modified with glutaraldehyde, formalin, 2,4,6-trinitrophenylate, Vibrio cholerae neurominidase, iodoacetate, heparin, histamine and adenosine 3'5'-monophosphate (cAMP), then used to immunize syngeneic CF1 mice. Animals immunized with the fixed (formalinized or glutaraldehyde fixed) neuraminidase-treated cells or the membrane of these cells, rejected two challenging doses of 10(8) viable unmodified adenocarcinoma cells. Animals immunized with adenocarcinoma cells treated with neuraminidase (170 IU/5x10(5) cells) or with the spontaneous adenocarcinoma-cell surface glycoprotein, rejected the first challenging dose but developed tumors and died on the second challenge with the viable untreated adenocarcinoma cells. Animals immunized with the adenocarcinoma cells pretreated with trinitrophenylate, glutaraldehyde or formalin, developed temporary resistance to the spontaneous mammary adenocarcinoma. Adenocarcinoma cells pretreated with NaF, iodoacetate, heparin, EDTA, Colchicine or histamine showed reduced oncogenicity and stronger resistance in mice to the development of a mammary tumor than to a smaller number (10(3) AdCa cells) of untreated viable adenocarcinoma cells. Cells treated with adenosine 3'5'-monophosphate accelerated tumor development.

Analytical fractionation of homogenates from cultured rat embryo fibroblasts

Homogenates of cultured rat embryo fibroblasts have been assayed for acid phosphatase, N-acetyl-beta-glucosaminidase, cathepsin D, acid deoxyribonuclease, cytochrome oxidase, NADH cytochrome c reductase, 5'-nucleotidase, inosine diphosphatase, acid pyrophosphatase, neutral pyrophosphatase, esterase, catalase, cholesterol, and RNA. The validity of the assay conditions was checked. Neutral pyrophosphatase is a readily soluble enzyme. Acid hydrolases, except acid pyrophosphatase, are particle-bound enzymes, which exhibit a high degree of structural latency. They are activated and solubilized in a parallel fashion by mechanical treatments and tensio-active agents. Catalase is also particle-bound and latent; activating conditions stronger than those for hydrolases are required to activate the enzyme. Acid pyrophosphatase, 5'-nucleotidase and inosine diphosphatase are firmly particle-bound, but not latent; they are not easily solubilized. In differential and isopycnic centrifugation, the latent hydrolases, cytochrome oxidase and catalase dissociate largely from each other; this suggests the occurrence of lysosomes and peroxisome-like structures besides mitochondria. The distribution patterns of 5'-nucleotidase and cholesterol are largely similar; digitonin influences their equilibrium density to the same extent; these two constituents are thought to be related to the plasma membrane. Inosine diphosphatase and acid pyrophosphatase are also partially associated with the plasma membrane, although some part of these enzymic activities probably belongs to other structures. NADH cytochrome c reductase is associated partly with the endoplasmic reticulum, partly with mitochondria.

The antigens of Mycoplasma hominis

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The uptake of lipids by rat liver cells

1. Unesterified cholesterol, cholesterol esters and triglycerides of chylomicrons were taken up at the same rate by isolated hepatic parenchymal cells. 2. On incubation of hepatic cells, isolated 2min. after the injection of chylomicrons in vivo, the chylomicron triglyceride associated with the cells underwent hydrolysis. 3. In cells isolated 5min. after the injection of chylomicrons, the chylomicron triglyceride bound to the hepatic cells was accessible to added clearing factor lipase. 4. ;Ghost' hepatic cells had the same binding capacity and lipolytic activity per cell as intact cells. 5. Of all subcellular fractions studied, the ;plasma membrane' fraction showed the greatest capacity per unit weight for non-esterified fatty acid and chylomicron triglyceride binding and for triglyceride hydrolysis. 6. Once non-esterified fatty acids entered the hepatic cell, they were apparently metabolized in the same manner, whether taken up from the circulation as such or derived from chylomicron triglyceride.

Plasma membranes: phospholipid and sterol content

The molar ratios of sterol to phospholipid in plasma membranes of five different types of rat cells range from 0.24 to 1.32. The composition of the plasma membrane of a cell has no fixed relation to that of the mitochondria. Thus the structure of cellular membranes shows both tissue and functional specificity.

SEPARATION AND PARTIAL PURIFICATION OF PLASMA-MEMBRANE FRAGMENTS FROM EHRLICH ASCITES CARCINOMA MICROSOMES

Membrane vesicles arising from the surface of Ehrlich ascites carcinoma cells were separated from the bulk of other microsomal components in Ficoll density gradients. Initial separation depends on the differential action of magnesium ion on various microsomal components. Immunologic and enzymic markers were used to monitor separation and purification steps.