Is there a plasma membrane-located anion-sensitive ATPase? III. Identity of the erythrocyte enzyme with (Ca2+ + Mg2+)-ATPase

The chloride pump: a Cl(-)-translocating P-type ATPase

Three widely documented mechanisms of chloride transport across plasma membranes are anion-coupled antiport, sodium-coupled symport, and an electrochemical coupling process. No direct genetic evidence has yet been provided for primary active chloride transport despite numerous reports of cellular Cl(-)-stimulated adenosine triphosphate (ATP)ases coexisting in the same tissue with uphill chloride transport that could not be accounted for by the three common chloride transport processes. Cl(-)-stimulated ATPases are a common property of practically all biological cells, with the major location being of mitochondrial origin. It also appears that plasma membranes are sites of Cl(-)-stimulated ATPase activity. Recent studies of Cl(-)-stimulated ATPase activity and chloride transport in the same membrane system, including liposomes, suggest a mediation by the ATPase in net movement of chloride up its electrochemical gradient across plasma membranes. Further studies, especially from a molecular biological perspective, are required to confirm a direct transport role to plasma membrane-localized Cl(-)-stimulated ATPases.

Reconstitution of a chloride-translocating ATPase from Aplysia californica gut

Basolateral membranes of Aplysia foregut epithelia contain both a Cl(-)-stimulated ATPase activity and an ATP-dependent Cl- transport. The protein responsible for both of these biochemical activities (Cl- pump) can be solubilized and reconstituted into liposomes with the aid of the detergent digitonin. Proteoliposomal Cl- pump activity was inhibited by vanadate.

Characteristics of ethacrynic acid highly sensitive Mg2+-ATPase in microsomal fractions of the rat brain: functional molecular size, inhibition by SITS and stimulation by Cl-

Studies were performed to characterize ethacrynic acid (EA) highly sensitive Mg2+-ATPase isolated from microsomal fractions of the rat brain. The functional molecular sizes of the EA highly sensitive and EA less sensitive Mg2+-ATPases, estimated by a radiation inactivation method, were 480 and 80 kDa, respectively. An anion transport inhibitor, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) inhibited the EA highly sensitive Mg2+-ATPase activity. The type of inhibition was uncompetitive with respect to ATP, and the inhibition was suppressed by anions such as Cl-, Br- and I-. Chloride ions stimulated enzyme activity with an increase in Vmax, but not in Km, for ATP. Anions tested also increased the enzyme activity in the following order of decreasing potency: Cl- greater than Br- greater than CH3COO- = I- greater than SO4(2-) = HCO3- greater than SO3(2-). These results suggest that EA highly sensitive Mg2+-ATPase is a relatively large molecule with anion-sensitive sites that affect the ATP hydrolyzing activity and the SITS binding capacity through anions, with Cl- being the most potent.

Antibodies against lysosomal membranes reveal a 100,000-mol-wt protein that cross-reacts with purified H+,K+ ATPase from gastric mucosa

Specific antibodies against lysosomal membranes were prepared by using techniques previously described (Louvard, D., H. Reggio, and G. Warren, 1982, J. Cell Biol., 92:92-107) for obtaining organelle-specific antibodies. The purified antibodies stained an acidic vacuolar compartment as shown by double-labeling experiments with acridine orange and indirect immunofluorescence. Characterization of the antibodies by immunoreplica methods revealed one major protein of approximately 100,000 mol wt. The antibodies cross-reacted with purified H+,K+ ATPase from pig gastric mucosa, the enzyme responsible for HCl secretion, but not with ATPases transporting other ions. They may therefore recognize a component of the proton pump involved in the acidification of lysosomes. As was expected, secondary lysosomes contained immunoreactive antigen, as determined by the fine-structural localization of reaction product for peroxidase or immunogold probes in several cell types. The antigen was also found in vacuoles containing phagocytosed bacteria in macrophages so it is present in at least some of the compartments of an endocytic pathway. In liver, the antigen was present in small amounts on the plasma membrane and in large amounts in some coated vesicles (near the sinusoidal surface of hepatocytes), putative endosomes, two cisternae on the cis side of the Golgi complex, adjacent vesicles and vacuoles, and pericanalicular dense bodies. In summary, the antigen seems to be present in those compartments that have recently been demonstrated to be acidified by an ATP-driven pump.

Inhibitor studies with adenohypophyseal granule membrane ATPase. Evidence for a membrane environment which modulates sensitivity to inhibitors

The limiting membranes of pituitary growth hormone and prolactin secretory granules contain a Mg2+-ATPase sensitive to anions. This enzyme is in many ways similar to mitochondrial ATPase. The enzyme was potently inhibited by oligomycin (Ki 6.5 X 10(-9) M), and was much more sensitive to the inhibitor than pituitary mitochondrial ATPase (Ki 2.7 X 10(-7) M). In contrast, the enzyme activity of intact secretory granules was only sparingly inhibited by oligomycin (maximal inhibition close to 30% at 5 X 10(-4) M). However, oligomycin (5 microM) did diminish to basal levels the enhanced granule ATPase activity observed in the presence of a stimulatory anion (25 mM sodium sulfite). Other compounds known to inhibit the proton translocating mitochondrial ATPase were also tested for their ability to inhibit the secretory granule ATPase. A similar pattern of limited inhibition in granules and greater sensitivity in isolated membranes was seen with the inhibitors N,N-dicyclohexylcarbodiimide and efrapeptin. In contrast, tri-n-butyltin chloride was a potent inhibitor of the ATPase of intact granules, and the susceptibility of the enzyme to inhibition by this compound was less after isolation of membranes. These observations suggest that pituitary secretory granule membrane ATPase may have a proton pumping function similar to that of the mitochondrial enzyme. In addition, the data imply that the inhibitor binding site(s) may be masked, inaccessible, or ineffective in intact granules, but exposed (or activated) in isolated membranes. The greater sensitivity of granule ATPase to tri-n-butyltin chloride, in contrast to the greater sensitivity of membrane ATPase to the other inhibitors, indicates that the tin compound may be effective at a membrane site(s) distinct from the others, or that the mechanism of inhibition is different.

The loop diuretic furosemide as non-competitive inhibitor of C1-/HCO3-ATPases of vertebrate kidneys and insect rectum

1. The effect of the diuretic drug furosemide was studied in detail on ouabain-insensitive, SCN- and OCN- -sensitive C1-/HCO-3-ATPase in homogenates from larval dragonfly rectum (Aeshna cyanea), frog (Rana temporaria) and mouse (Mus musculus) kidney. 2. The in vitro inhibition by the drug studied on the HCO-3-activated enzyme is non-competitive with an inhibitor constant of Ki=4.3 mM furosemide in the case of insect rectum and Ki=0.9 mM furosemide in the case of frog and mouse kidney. 3. Furosemide even at 10 mM concentration which completely inhibits the anion-dependent ATPase has only a little inhibitory effect on the Na+/K+-ATPase of the 3 tissues. 4. The data suggest that furosemide may affect an active chloride transport system involving a C1-/HCO-3-ATPase.

Transport ATPases in anion and proton transport

Studies in our laboratory have shown that the anion-sensitive Mg-ATPase is located in mitochondria, but not in the plasma membrane of rabbit gastric mucosa, trout gill, rabbit kidney and rat pancreas; whereas in rabbit erythrocyte membrane, it is part of the Ca-Mg activated ATPase system. These findings appear to rule out a function of the anion-sensitive ATPase in the transport of anions and protons across the plasma membrane in these tissues. On the other hand, the K-activated ATPase in a gradient-purified vesicle fraction of pig gastric mucosa mediates proton uptake in exchange for K+ in the presence of ATP, in agreement with earlier findings of other investigators. The enzyme requires a phospholipid environment for its activity. Studies of arginine modification with butanedione in the presence or absence of ATP and its analogues, and of activating cations indicate that the enzyme contains an essential arginine group involved in ATP binding; and that K+ induces a conformational change, which leads to decreased ATP binding and probably coincides with enzyme dephosphorylation. Similar studies of sulfhydryl modification with DTNB indicate that the enzyme contains an essential sulfhydryl group, which does not appear to be directly involved in ATP binding, but rather that ATP binding may induce a conformational change which makes the sulfhydryl group less accessible.

Adenosine triphosphatase localization in the branchial heart appendage of Sepia officinalis L. (Cephalopoda)

Sodium- and potassium-dependent adenosine triphosphatase (Na+--K+-ATPase) has been demonstrated in the branchial heart appendage (pericardial gland) of Sepia officinalis L. by biochemical, cytochemical and autoradiographical methods. The biochemical data indicate the presence of Na+--K+-ATPase, judging from the potassium dependency and, with some restrictions, the inhibition by ouabain. Cytochemically and autoradiographically, the enzyme could be localized on the cytoplasmic surfaces of the lateral plasma membranes and the basal membrane infoldings (basal labyrinth) of the folded epithelium of the branchial heart appendage. The pdocytes of the peripheral zone of the organ reacted negatively. In addition to the Na+--K+-ATPase, a magnesium-activated adenosine triphosphatase (Mg2+-ATPase) was demonstrated in the folded epithelium, localized mainly in the mitochondria but also at the brush border and in the apical intercellular space, whereas a bicarbonate-stimulated ATPase (HCO-3-ATPase) was present only in the mitochondria.

Is there a plasma membrane-located anion-sensitive ATPase? IV. Distribution of the enzyme in rat pancreas

The intracellular localization of anion-sensitive Mg2+-ATPase in rat pancreas was studied by differential centrifugation, density gradient centrifugation and by the use of inhibitors of mitochondrial Mg2+-ATPase. The anion-sensitive MG2+-ATPase appears to be localized almost exclusively in a mitochondrial (15 min, 15 000 times g) fraction which shows two peaks after density gradient centrifugation. Both peaks coincide with the highest levels of cytochrome c oxidase activity, but not with alkaline phosphatase, (Na+ plus K+)-ATPase and leucine aminopeptidase activities or RNA. They appear to be equal sensitive to inhibition by oligomycin, aurovertin D and the rat liver mitochondrial inhibitor protein, at least when 1 mM EDTA is present in the isolation media. We conclude that no significant plasma membrane-located anion-sensitive Mg2+-ATPase activity is present in rat pancreas.