ATPase expression

The pharmacological receptor of cardiac glycosides is the sarcolemmal Na+/K+-ATPase expressed on most eucaryotic membranes. It was characterised biochemically in 1957 by J. Skou, who was awarded with the Nobel Prize in chemistry in 1997. The sodium... 

The H,K-ATPase, expressed in the parietal cells of the stomach, transports H+ ion from cytoplasm to lumen in exchange for extracytoplasmic K+ ion in an electroneutral exchange using the energy of ATP hydrolysis. 

The secretion of CSF and ECF is essentially driven by an osmotic gradient created by the Na+/K+-ATPase, expressed in the abluminal membrane of the BBB endothelium and the apical membrane of the choroid plexus epithelium, which produces water movement into brain ECF and produces volume secretion. 

Nabekura, T., Tomohiro, M., Ito, Y., Kitagawa, S., 2004, Changes in plasma membrane Ca2+ -ATPase expression and ATP content in lenses of hereditary cataract UPL rats. Toxicology 197, 177-183. 

Morsomme, R, d Exaerde, A. D., DeMeester, S.,Thines,D., Goffeau, A., and Boutry, M. (1996). Single point mutations in various domains of a plant plasma membrane H+-ATPase expressed in Saccharomyces cerevisiae increase H+- pumping and permit yeast growth at low pH. EMBO J. 15, 5513-5526. 

An H+ electrochemical gradient (ApH+) provides the energy required for active transport of all classical neurotransmitters into synaptic vesicles. The Mg2+-dependent vacuolar-type H+-ATPase (V-ATPase) that produces this gradient resides on internal membranes of the secretory pathway, in particular endosomes and lysosomes (vacuole in yeast) as well as secretory vesicles (Figure 3). In terms of both structure and function, this pump resembles the F-type ATPases of bacteria, mitochondria and chloroplasts, and differs from the P-type ATPases expressed at the plasma membrane of mammalian cells (e.g., the Na+/K+-, gastric H+/K+-and muscle Ca2+-ATPases) (Forgac, 1989 Nelson, 1992). The vacuolar and F0F1... 

Figure 17. Analysis of phosphoenzyme intermediates of SR Ca2+-ATPase mutants with alterations to carboxylate-containing residues in the transmembrane sector. Wild-type or mutant Ca2+-ATPases expressed in the endoplasmic reticulum membranes of COS-1 cells were phosphorylated with [y-32P] ATP (panel a) or [32P]P (panels b and c). Following acid-quench of the phosphorylated intermediate, the samples were subjected to SDS-polyacrylamide gel electrophoresis under acid pH conditions and the dried gels were autoradiographed to visualize the radioactivity associated with the covalently bound phosphate. Panel a shows the Ca2+-concentration dependence of phosphorylation from ATP. The Glu309- Lys mutant is unable to phosphorylate, even at 12.5 mM Ca2+. In the wild-type Ca2+-ATPase the phosphorylation reaction is fully saturated at 10 pM Ca2+. Panel b shows lack of Ca2+ inhibition of backdoor phosphorylation from P in the mutants. E indicates the presence of ECTA to chelate Ca2+ (normally a requirement for phosphorylation by the backdoor route). C indicates the...

Maruyama, K. MacLennan, D.H. (1988). Mutation of aspartic acid-351, lysine-352, and lysine-515 alters the Ca2+ transport activity of the Ca2+-ATPase expressed in COS-1 cells. Proc. Natl. Acad. Sci. USA 85,3314-3318. 

The expansion of our knowledge of the structure and function of Na,K-ATPase is reflected in a rapid succession of reviews on Na,K-ATPase genes and regulation of expression [17], subunit assembly and functional maturation [20], the isozymes of Na,K-ATPase [18], and the stability of a subunit isoforms during evolution [21], physiological aspects and regulation of Na,K-ATPase [22], reconstitution and cation exchange [23], chemical modification [24], and occlusion of cations [25]. Other valuable sources are the review articles [26] and recent developments [27] reported at the International Na,K-pump Conference in September 1990. 

It is well known that chemical compo.sition of rhizosphere solution can affect plant growth. Particularly, uptake of nutrients may be considerably influenced by the ionic concentration of the rhizosphere solution (40). Despite the difficulty of defining the exact concentration of ions in the rhizosphere surrounding each root (or even root portion), it has been unequivocally demonstrated that plants have evolved mechanisms to cope with the uneven distribution of ions in the root surrounding in order to provide adequate supply of each essential nutrient (41). These mechanisms include expression of transporter genes in specific root zones or cells and synthesis of enzymes involved in the uptake and assimilation of nutrients (40,43). Interestingly, it has been shown that specific isoforms of the H -ATPase are expressed in the plasma membrane of cell roots it has been proposed that the expression of specific isoforms in specific tissues is relevant to nutrient (nitrate) acquisition (44) and salt tolerance (45). 

Na,K-ATPase is a heterodimer consisting of a catalytic a-subunit and an accessory p-subunit. Four isoforms of the a-subunit and three of the P-subunit are expressed in mammals. Three of the a-subunit isoforms are expressed in brain and will be discussed in a later section. 

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