ATPase ATP synthase

RING finger proteins may have other domains associated with signal transduction, such as SH3 and STAT domains and domains that bind and effect hydrolysis of nucleotides in signal transduction or for other purposes. These include ATPases, ATP synthases, serine/threonine kinases, GTP-binding domains, ADP-ribosylation domains and AAA-superfamily ATPases (http //home.cancer.gov/lpds/weissman). 

FIGURE 11-39 Structure of the F F] ATPase/ATP synthase. F-type ATPases have a peripheral domain, F, consisting of three cr subunits, three j3 subunits, one S subunit (purple), and a central shaft (the y subunit, green). The integral portion of F-type ATPases, F0 (yellow), has multiple copies of c, one a, and two b subunits. F0 provides a transmembrane channel through which about four protons are pumped (red arrows) for each ATP hydrolyzed on the j3 subunits of F,. The remarkable mechanism by which these two events are coupled is described in detail in Chapter 19. It involves rotation of F0 relative to F, (black arrow). The structures of V0Vi and AoA, are essentially similar to that of F0F, and the mechanisms are probably similar, too. 

F0Fi ATPase/ATP synthase of mitochondrial inner 19-58 membrane, chloroplast thylakoid, and bacterial plasma membrane... 

Yamada, H., Moriyama, Y., Maeda, M., and Futai, M. (1996). Transmembrane topology of Escherichia coli H(+) -ATPase (ATP synthase) subunit a. FEBS Lett. 390, 34-38. 

At present, much attention is devoted to enzymes that utilize the energy of ATP hydrolysis for realization of energy-rich mechanics (myosin), transport (Na+,K+-ATPase, Ca2+-ATPase, chemical processes (nitrogenase), polymerases, topoisomerases, GTPases, and for creation of electrochemical gradients in biomembranes (H+-ATPase, ATP synthase ). In this section we focus on the latter process. The coupling mechanism in the nitrogenase reaction is discussed in Section 3.1. 

The idea that oxidative phosphorylation and photophosphorylation systems are coupled with the transfer of a proton through the membrane was introduced by Mitchell (1966) and is now widely accepted. H+-ATPase (ATP synthase, F,Fo-ATPase) catalyzes ATP synthesis coupled to an electrochemical gradient and ATP hydrolysis driven by proton translocation in mitochondrial or bacterial membranes. (Boyer, 2001 Babcock and Wikstroem, 1992 Abraham et al., 1994 Allison, 1998 Ogilvie et al. 1997 Musser and Theg, 2000 Backgren et al., 2000 Arechada and Jones, 2001 Gibbsons et. al., 2000 and references therein). The enzyme from Escherichia coli consists of two parts, a water-... 

The spheres removed from SMPs do not support ATP synthesis but do hydrolyze ATP to ADP and phosphate. Thus, ATP synthesis is carried out by Fq/Fi—ATPase (ATP synthase). The subscript o in Fq indicates that it contains the site at which a potent antibiotic inhibitor, oligomycin, binds and inhibits oxidative phosphorylation. Oligomycin does not bind Fi-ATPase and does not inhibit ATP hydrolysis to ADP and phosphate. 

Blocking of the proton gradient between NADH-Q reductase and QH2 Blocking of the proton gradient between cytochrome Cj and cytochrome c Dissociating of cytochrome c from mitochondrial membranes Inhibiting of mitochondrial ATPase (ATP synthase)... 

Zheng J, Ramirez VD (2000) Inhibition of mitochcmdrial proton FOFl-ATPase/ATP synthase by polyphenolie phytoehemieals. Br J Pharmacol 130 1115—1123... 

The H" "-translocating ATPase ( ATP-synthase ) from chloroplasts is a membrane-bound enzyme which can couple a transmembrane proton transport with ATP synthesis/hydrolysis. 

The ATPase complex of chloroplasts (H -ATPase, ATP-synthase) carries out synthesis (hydrolysis) of ATP coupled with transmembrane transport of hydrogen ions. This complex consists of a hydrophylic catalytic part called coupling factor CF, and a hydrophobic part, CFq, the function of which is to translocate protons towards CF. CFj can bind as many as six nucleotide molecules / /. After CF precipitation by ammonium sulfate with subsequent gel filtration, the enzyme retains about 1 mol of tightly bound nucleotides consisting mainly of ADP /2/. 

The F,Fo type of ATPases/ATP synthases is found in the inner bacterial, chloroplast, and mitochondrial membranes and catalyzes the synthesis of ATP from ADP and inorganic phosphate (P,) by dissipation of the electrochemical gradient of H generated across these membranes by oriented redox pumps. Working in reverse, they are able to pump H. ... 

The mitochondrial complex that carries out ATP synthesis is called ATP synthase or sometimes FjFo-ATPase (for the reverse reaction it catalyzes). ATP synthase was observed in early electron micrographs of submitochondrial particles (prepared by sonication of inner membrane preparations) as round, 8.5-nm-diameter projections or particles on the inner membrane (Figure 21.23). In micrographs of native mitochondria, the projections appear on the matrixfacing surface of the inner membrane. Mild agitation removes the particles from isolated membrane preparations, and the isolated spherical particles catalyze ATP hydrolysis, the reverse reaction of the ATP synthase. Stripped of these particles, the membranes can still carry out electron transfer but cannot synthesize ATP. In one of the first reconstitution experiments with membrane proteins, Efraim Racker showed that adding the particles back to stripped membranes restored electron transfer-dependent ATP synthesis. 

Complex V (ATP Synthase, Mitochondrial Proton-Translocating ATPase)... 

F-ATPases (including the H+- or Na+-translocating subfamilies F-type, V-type and A-type ATPase) are found in eukaryotic mitochondria and chloroplasts, in bacteria and in Archaea. As multi-subunit complexes with three to 13 dissimilar subunits, they are embedded in the membrane and involved in primary energy conversion. Although extensively studied at the molecular level, the F-ATPases will not be discussed here in detail, since their main function is not the uptake of nutrients but the synthesis of ATP ( ATP synthase ) [127-130]. For example, synthesis of ATP is mediated by bacterial F-type ATPases when protons flow through the complex down the proton electrochemical gradient. Operating in the opposite direction, the ATPases pump 3 4 H+ and/or 3Na+ out of the cell per ATP hydrolysed. 

Transport ATPases transport cations—they are ion pumps. ATPases of the F type—e. g., mitochondrial ATP synthase (see p. 142)—use transport for ATP synthesis. Enzymes of the V type, using up ATP, pump protons into lyso-somes and other acidic cell compartments (see p. 234). P type transport ATPases are particularly numerous. These are ATP-driven cation transporters that undergo covalent phosphorylation during the transport cycle. 

The concept of rotational catalysis by ATP synthase is based on (a) P and 0 exchange rate data attesting to strong cooperativity with sequential participation of several catalytic sites (b) Pi and ATP 0-isotopomer distributions indicating that all catalytic sites exhibit identical catalysis and (c) that catalysis is strongly influenced by the y-subunit whose primary structure was not likely to account for spatially similar interactions with the /3-subunits . The model was found to be compatible with the 2.8 A resolution structure of bovine heart mitochondrial Fi-ATPase. ... 

Transporting ATP synthase [EC 3.6.1.34] in plants, also referred to as chloroplast ATPase and CFiCFo-ATPase, catalyzes the hydrolysis of ATP to produce ADP and orthophosphate. When coupled with proton transport the reverse reaction results in the synthesis of ATP by this multisubunit complex. CFi, isolated from the rest of the membrane-bound complex, retains the ATPase activity but not the proton-translocating activity. 

In the Walker crystal structure of Fj-ATPase, the three non-catalytic a sites are liganded with the non-hydrolyzable ATP analog MgAMP-PNP. In contrast, the three catalytic (3 sites possess different conformations. One of the catalytic sites in the structure binds the analog MgAMP-PNP and is designated as Pjp another site binds MgADP and is denoted by (3dp, while the third site is empty and distorted and is called (3e [21]. In further contrast, the nucleotide-free subcomplex of ATP synthase is a symmetric trimer [36]. 

The activity of complex V (ATP synthase) can be conveniently measured in the reverse direction, ATP hydrolysis with a coupled assay thereafter described [72] (Fig. 3.8.6). The use of oligomycin, a specific inhibitor of the enzyme, allows discrimination of the mitochondrial enzyme from any nonmitochondrial ATPases. 

Ca2+ cycling into and out of the mitochondria leads to NAD depletion and a fall in ATP. The entry of Ca2+ into the mitochondria dissipates the potential difference across the mitochondrial membranes and so inhibits the function of ATP synthase, which relies on the charge difference across the membrane (Fig. 6.13 and 7.60). Export of Ca2+ from the mitochondrial matrix may occur and be stimulated by some chemicals. However, this will lead to repeated cycling, which damages the membrane and further compromises ATP synthesis. The export of Ca2+ also uses up ATP as a result of the Ca2+ ATPases involved. Hence ATP levels fall. 

The reaction catalyzed by F-type ATPases is reversible, so a proton gradient can supply the energy to drive the reverse reaction, ATP synthesis (Fig. 11-40). When functioning in this direction, the F-type ATPases are more appropriately named ATP synthases. ATP synthases are central to ATP production in mitochondria during oxidative phosphorylation and in chloroplasts during photophosphorylation, as well as in eubacteria and archaebacteria. The proton gradient needed to drive ATP synthesis is produced by other types of proton pumps powered by substrate oxidation or sunlight. As noted above, we return to a detailed description of these processes in Chapter 19. 

P-type ATPases 398 SERCA pump 400 F-type ATPases 401 ATP synthase 401 V-type ATPases 401 ABC transporters 402 multidrug transporter 402... 

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