Vacuolar ATPases enzymes

AThe subunit has been confirmed for the insect (Merzendorfer et al, 1999) and chromaffin granule enzyme (Ludwig et al, 1998) and has recently been found in the yeast enzyme (Sambade and Kane, 2004). The subunit compositions of the F-ATPase from the bacterium Escherichia coli, the vacuolar ATPase from yeast and bovine brain clathrin-coated vesicles, and the A-ATPase from the Archaeon Thermoplasma acidophilum are listed. Molecular masses are calculated from the amino acid sequence where available. 

The enzyme proved to be composed of four types of subunits (87, 60, 29 and 20 kDa). The subunit ratio was assumed to be equal to 3 3 1 1 [66]. The sequences of major subunits showed significant (more than 50%) homology with the detachable sector of eukaryotic vacuolar (V-type) H -ATPase. On the other hand, homology with bacterial Fi ATPase proved to be less than 30%. Since the above-mentioned inhibitor pattern is, in fact, identical with those of the vacuolar ATPase, one might assume that halobacterial ATPase corresponds to the V-type. However, the sequence of proteolipid (c subunit) of... 

Three types of ATP-driven cation pumps can be distinguished on the basis of their structure and their sensitivity to inhibitors. They are the E E2-ATPases, the FiFo-proton-translocating ATP synthase, and the vacuolar ATPases which are designated as P-, F-, and V-type ATPases, respectively [37]. Several of the distinguishing characteristics of these enzymes are summarized in Table 1. The F- and V-ATPases can be differentiated by the sensitivity of the former to azide and the latter to nitrate and A-ethylmaleimide (NEM)[38]. In addition, the V-ATPases are exquisitely sensitive to the antibiotic bafilomycin A [39,40]. 

Bafilomycin Al, Bl, Cl and concanamycin belong to the plecomacrolide family and were isolated from various Streptomycetes strains. Plecomacrolide antibiotics exhibit a wide spectrum of activities, including antifungal, antimalarial, antiparasitic, and antitumor properties. They also show high-affinity inhibition of vacuolar (V-type) ATPase enzymes that are involved in the bone resorption processes in osteoclasts. They can be used in the treatment of osteoporosis. 

Proton-ATPases can be divided into three classes a) The plasma-membrane type, which operates via a phosphoenzyme intermediate and therefore is part of the P-ATPase superfamily. These proton pumps evolved from a common ancestor of the Ca" and Na pumps and are structurally distinct from the other two families of proton pumps (1-3). b) The eubacterial-type F-ATPases that are present in eubacteria, mitochondria and chloroplasts (3,4). c) The vacuolar-type V-ATPases that are present in archaebacteria and the vacuolar system of eukaryotic cells (2-6). F and V-ATPases are structurally and functionally related and have evolved from a common ancestral enzyme (3,4). This relationship was established from a wealth of sequence information regarding F-ATPases and by more recent studies on V-ATPases. The divergent pathways by which F and V-ATPases have evolved were recently elucidated by pai lel studies in several laboratories (3). It is the piupose of this communication to discuss aspects pertinent to the evolution of CFq-CFi, which is the F-ATPase functioning in photosynthesis. 

Self-referencing ion-selective electrodes have seen attractive applications in a diversity of medical problems. For example, the vacuolar-type H+-ATPase has been shown to play an important role in the acidification of the lumen of the proximal vas deferens, part of the male reproductive system. An acidic luminal fluid is required for the maintenance of sperm quiescence and for the prevention of premature activation of acrosomal enzymes during their storage in the epididymis and vas deferens. Proton secretion in the proximal vas deferens has been measured with the self-referencing technique (Fig. 6) [40]. Likewise, altered potassium homeostasis is indicative of dying cells, as the transplasma membrane potential is no longer maintained, as measured in both viable and nonviable embryos [41]. 

Both omeprazole and pantoprazole react with vacuolar H ATPase, as inferable from their abilities to inhibit acidification in purified kidney lysosomes [27]. However, they did so with low potencies, concentrations needed for half-maximal inhibition (IC50) being 75 and 195 pmol/1, respectively. Protection of the enzyme by 10 p.mol/1 glutathione suggested an extralysosomal action (at the neutral pH of the incubation medium), rather than an effect secondary to intralysosomal activation. 

The vacuoles in higher plants are essential for the maintenance and regulation of the homeostatic environment of the cells [1]. The vacuolar membranes of plant cells contains an electrogenic H -ATPase which provides the proton-motive force for the active transport of solutes across the vacuolar membranes. The activities of certain membrane-bound enzymes are lost by the removal of constituted lipids, but are restored after the addition of exogenous phospholipids [2,3]. Kasamo [4] showed that the various molecular species of PC activated to different extents the H -ATPase solubilized from the plasma membrane of rice cultured cells. 

Vacuolar H-l—ATPases are highly conserved evolutionarily ancient enzymes located on membranes of vacuoles, lyso-somes, and other organelles, as well as on certain specialized plasma membrane. They are responsible for the pH regulation of intracellular compartments of eukaryotes, which is essential for many cellular processes. 

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