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PubMed2001

Structure of the vacuolar adenosine triphosphatases.

Vacuolar adenosine triphosphatases (V-ATPases) represent an important class of proton pumps found in endomembrane systems of eucaryotic cells, where they are involved in pH regulation. Progress has been made in the structure determination of this large, membrane-bound multisubunit enzyme complex. Electron microscopy of the V-ATPase has revealed a ball-and-stalk-like structure similar to F1F0-type ATP synthase, to which the V-ATPase is evolutionary related. Aside from the overall structural similarity of the V-ATPase and F-ATP synthase, a number of distinct structural differences exist between the two related enzymes, giving clues to their different function and regulation in the organism.

Adenosine Triphosphate↗
PubMed1976

A method for determining the adenosine triphosphatase content of energy-transducing membranes. reaction of 4-chloro-7-nitrobenzofurazan with the adenosine triphosphatase of bovine heart submitochondrial particles.

1. Modification of a single amino acid residue by introduction of the nitrobenzofurazan group inactivates mitochondrial ATPase (adenosine triphosphatase) when membrane-bound in submitochondrial particles. The similarity between the reactions of both membrane-bound and isolated ATPase with 4-chloro-7-nitrobenzofurazan indicates that the single essential tryosine residue identified in the isolated enzyme [Ferguson, Loyd, Lyons & Radda (1975) Eur. J. Biochem. 54, 117-126] Is also a feature of the membrane-bound ATPase. 2. A procedure is presented for estimating the ATPase content of the inner mitochondrial membrane. It is based on the specificity of the incorporation of the nitrobenzofurazan group, and the ready removal of this group by compounds that contain a thiol group. This method indicates that 8.5% of the membrane protein is ATPase. The procedure should be applicable to the titration of the energy-transducing ATPases of bacterial plasma membranes and of the thylakoid membranes of chloroplasts. 3. Combination of the data obtained on the ATPase content of the bovine heart inner mitochondrial membrane with a titration of the cytochrome bc1 complex with antimycin indicates that these two components of the membrane are present in approximately equal amounts.

Adenosine Triphosphatases↗
PubMedDate not supplied

[Study of the amino acid residue topography of the adenosine triphosphatase center of (Ca--Mg)-dependent sarcoplasmic reticulum adenosine triphosphatase by kinetic and spectral methods].

The topography of HS- and NH2-groups and tryptophane residues in ATPase centre of (Ca--Mg)-ATPase on sarcoplasmic reticulum (SR) was investigated by kinetics, electron spectroscopy and spectrofluorimetry method. Both o-phthalaldehyde interacting with lysine or arginine residue or with end amino acid and fluorescein dimercuric acetate interaction with cysteine residue of HS-groups make (Ca--Mg)-ATPase both in SR and the pure enzyme completely inactive at molar ratio enzyme: inhibitor equal to 1 : 1. A 500 molar ATP surplus reduces drastically the enzyme inactivation rate by both inhibitors. The data supplied by the spectrofluorimetry and the induction-resonance theory were used to calculate the distances between nearest tryptophane residues and chromophore (o-FTC) generated by o-phthalaldehyde interaction with NH2-group the protein amino acid residue (17 A) and o-FTC and fluorescein dimercuric acetate (19 A) attached to enzyme HS-group. Because o-FTC is inside the protein pocket it is not accessible to J- ions up to 2.5 M KJ. However some tryptophane resudies and fluorescein dimercuric acetate attached to HS-group are near to the macromolecule surface. Lysine (or arginine residues) or end amino acid NH2-group and cysteine residues HS-group, and some tryptophane residues are at ATPase centre of (Ca--Mg)-ATPase from sarcoplasmic reticulum. Possible topography of the centre is discussed.

Amino Acids↗
PubMed1976

Phospholipid-protein interactions in the Ca2+-adenosine triphosphatase of sarcoplasmic reticulum.

Ca2+-adenosine triphosphatase from sarcoplasmic reticulum has been delipidated by gel filtration through a Sephadex G-200 column equilibrated with buffer containing cholate. The delipidated Ca2+-adenosine triphosphatase had negligible adenosine triphosphatase activity, but up to 50% of the ATPase activity was restored when the delipidated enzyme was recombined with phosphilipids. It was shown with the delipidated preparation that the phosphorylation of the enzyme by either ATP or Pi was entirely dependent on phospholipids. Among the purified phospholipids, phosphatidylcholine reactivated the adenosine triphosphatase activity better than phosphatidylethanolamine. Vesicles capable of translocating Ca2+ were reconstituted from delipidated Ca2+-adenosine triphosphatase and phosphatidylethanolamine, but not with phosphatidylcholine alone. We conclude that the firmly bound phospholipids which are purified together with the adenosine triphosphatase protein are not essential for the pump since they can be substituted by phosphatidylethanolamine isolated from soybeans.

Adenosine Triphosphatases↗
PubMed1977

Bacillus megaterium mutant deficient in membrane-bound adenosine triphosphatase activity.

An adenosine triphosphatase (ATPase) mutant of Bacillus megaterium was isolated and characterized. This mutant (designated A37) was unable to grow on nonfermentable carbon sources and possessed less than 5% of the wild-type ATPase activity. Oxygen uptake by the mutant was comparable to that in the wild type. Sporulation in the wild type occurred in both glucose- and nitrogen-limiting media; however, A37 sporulated only in the nitrogen-limiting medium. The inability of A37 to sporulate in glucose-limiting medium seemed to be due to insufficient adenosine 5'-triphosphate (ATP) levels during the sporulation stages. Fructose, which can generate ATP via substrate-level phosphorylation, is equally efficient in stimulating ATP synthesis in the wild type and A37. Malate-stimulated ATP synthesis in the wild type was shown to have many characteristics associated with oxidative phosphorylation and was absent in the mutant. These data suggest that the ATPase deficiency results in the loss of oxidative phosphorylation.

Adenosine Triphosphatases↗
PubMed1980

Radiolabeling of natural adenosine triphosphatase inhibitor with phenyl (14C)isothiocyanate and study of its interaction with mitochondrial adenosine triphosphatase. Localization of inhibitor binding sites and stoichiometry of binding.

The natural ATPase inhibitor (IF1) from beef heart mitochondria was labeled with phenyl (14C)isothiocyanate [(14C)PITC]. Chemical labeling by (14C)PITC does not modify the inhibitory properties of IF1, provided the number of residues of (14C)PITC bound per molecule of IF1 is lower than five to six, which corresponds to the average labeling of roughly half of the available lysine residues in IF1. This partially labeled, fully active, IF1 was used to determine the binding stoichiometry of IF1 with respect to F1 and to localize the inhibitor binding sites in F1-ATPase. The pattern of loss of ATPase activity of F1 with increasing amounts ot (14C)PITC-IF1 indicated that the ATPase activity is fully inhibited when 1 mol of IF1 is bound to 1 mol of F1. As F1 contains at least 2 beta subunits, this points to a half-site reactivity of F1 with respect to IF1. Sites of interaction between (14C)PITC-IF1 and F1 subunits were investigated by the use of two cross-linking reagents which act as "zero length" cross-linkers, 1-ethyl-3-[(dimethylamino)propyl]carbodiimide (EDAC) and N-(ethoxycarbonyl)-2-ethoxydihydroquinoline (EEDQ); the products of cross-linking were analyzed by NaDodSO4-polyacrylamide gel electrophoresis. IF1 was found to bind preferentially to the beta subunit of F1. Among the cross-linked products formed by reaction of EDAC or EEDQ with subunits of F1, one of them, the beta gamma dimer, did not accumulate when IF1 was added to F1 prior to cross-linking.

Adenosine Triphosphate↗
PubMed1980

Brain capillary guanosine triphosphatase: a distinction from adenosine triphosphatase.

Differences in kinetic properties, pH response, sensitivity to ouabain, and disc-acrylamide electrophoresis resolution, are observed when GTP and ATP are used as the substrates for triphosphohydrolases in isolated rat brain microvessels. In brain parenchyma there are no such differences. It is concluded that substrate-specific GTPase exists in brain microvessels.

Adenosine Triphosphatases↗