A ATPases

The F-, V-, and A-ATPases constitute a family of ATP hydrolysis-driven ion pumps which are found in Archaea, eubacteria, simple eukaryotes such as yeast, and higher eukaryotes including plants and mammals. The family of ion pumps is divided into three subfamilies the F-ATPases (which function mainly as ATP synthases), the vacuolar ATPases (which function solely as ATP hydrolysis-driven ion pumps) and the Archaeal A-type ATPases (whose function can be either in the direction of ATP synthesis or hydrolysis). All three members of the family are evolutionarily related, and it is believed that the three subfamilies have arisen from a common ancestor. 

A unique feature of the F/V/A-ATPases is that they are rotary molecular motor enzymes. This has been shown by experiment for members of the F-and V-ATPase subfamilies and is generally assumed to be true for the closely related A-ATPases as well. The two enzymatic processes, ATP synthesis/hydrolysis and ion translocation, are coupled via a rotational motion of a central domain of the complex (the rotor) relative to a static domain (the stator). The A-, F-, and V-ATPases represent the smallest rotary motors found in the living cell so far. Most of what we know about the structure and mechanism of these microscopic energy converters comes from studies conducted with the F-ATPase. In the following review, current structural knowledge for all three members of the family of F-, V-,... 

Subunit Composition of the FiF0-ATP Synthase, the Eukaryotic Vacuolar ATPase and the Archaeal A-ATPase... 

The subunit nomenclature for the A-ATPase is Kfor the proteolipid, I for the V- and F-ATPase a-subunit, and C for the V-ATPase subunit d. The small polypeptide called H in the A-ATPase is probably the homologue of the V-ATPase G-subunit. 

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. 

Fig. 1. Working models of the F-, V-, and A-ATPases. Model of the subunit arrange-mentin the (A) FjFo-ATP synthase from Escherichia colt, (B) vacuolar ATPase from bovine brain clathrin- coated vesicles, and (C) A A0-ATPase from Thermoplasma acidophilum. The catalytic domain is in blue, the rotor domain is in green, and the stator domain is in orange.

Enzymes that are structurally related to the eukaryotic V-ATPase are also found in certain eubacteria (Speelmans etal., 1994 Takase etal., 1994 Yokoyama etal., 1990). Based on nucleotide sequence analysis, it is believed that these bacterial V-like ATPases have been introduced into the eubacteria via horizontal gene transfer from Archaea (Hilario and Gogarten, 1993, 1998). The subunit composition of the bacterial V-like ATPase is indeed more similar to the archaeal A-ATPase than to the eukaryotic V-ATPase, and we will therefore treat the bacterial V-ATPase—like enzyme together with the archaeal A-ATPase (see below). In the following, we will use the name V-ATPase only for the eukaryotic enzyme, and we will call the bacterial enzyme the A/V-type ATPase as suggested by Hilario and Gogarten (1998). 

II. Overall Structural Features of the F-, V-, and A-ATPases A. Structure of the F-ATPase... 

Based on sequence comparison, the eubacterial V-type ATPase is a product of horizontal gene transfer from the Archaea. Much of the information about the subunit arrangement in the eubacterial A/V-type—like ATPase comes from studies with the enzymes from C. fervidus and T. thermophilus (Boekema et al, 1997, 1999 Ubbink-Kok et al, 2000 Yokoyama et al, 2003a). A recent 3D reconstruction of the A/V- ATPase from T. thermophilus (Bernal and Stock, 2004) revealed the structural similarity to both the eukaryotic V-ATPase (Domgall et al., 2002 Wilkens et al., 2004, 2005) and the archaeal A-ATPase (Coskun et al., 2004a,b). The x-ray crystal structure for the C-subunit of the bacterial A/V-like ATPase has been reported recently (Iwata et al, 2004). The C-subunit of the bacterial V-like ATPase shows limited but significant sequence homology to the cZ-subunit of the eukaryotic V-ATPase. 

Hilario, E., and Gogarten, J. P. (1998). The prokaryote-to-eukaryote transition reflected in the evolution of the V/F/A-ATPase catalytic and proteolipid subunits./ Mol. Evol. 46, 703-715. 

Fig. 9. (Panel A) ATPase activity assay in the rat homogenate expressed as pMol min-1 mg-1 protein, either in the controls or in the presence of different concentrations of Al(III). Bars SD P< 0.01. (Panel B) ATPase activity assay in rat liver mitochondria expressed as pMol min-1 mg-1 protein, in the controls or in presence of 9 pM Al(III). Bars SD. P<0.01. Data are from Zatta et al. (1995) [34]...

Once thyroid hormone enters a cell, it binds temporarily with a spt plasmic protein. Thyroid hormone molecules migrate to the nucleus chondria, where they bind to receptors. In the nucleus the binding hormone initiates the transcription of genes that play crucial roles i of cellular processes, such as those that code for growth hormone a ATPase. In mitochondria, thyroid hormones promote oxygen consur increased fatty acid oxidation. (The mechanism by which this latter pro< is not understood.)... 

A. ATPase and Motor Properties of Smooth Muscle Myosin... 

Grandmougin A. ATPase-H+ dc la membrane plasmique de racines de mai s r61e des st6rols [thesis]. Strasbourg Univ. Louis Pasteur, 1989. 

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