A proteolipid associated with Na,K-ATPase is not essential for ATPase activity

Hardwicke, Peter M.D.; Freytag, J W

doi:10.1016/0006-291x(81)91514-x

Cited by 37 publications

(28 citation statements)

References 15 publications

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“…It belongs to the FXYD family, a group of small (7.5-19 kDa) single-span membrane proteins, characterized by the presence of the FXYD motif in the extracellular domain, and that includes phospholemman, channel-inducing factor (CHIF), and other peptides (430). The ␥-subunit is not required for catalytic activity (207) but modulates Na ϩ pump function by changing the affinity for ATP, Na ϩ , and/or K ϩ (10,366,446,447). It is synthesized from a gene with two different promoter regions that provide differential expression of the two splice variants known (264,430).…”

Section: The ␥-Subunitmentioning

confidence: 99%

Cell Adhesion, Polarity, and Epithelia in the Dawn of Metazoans

Cereijido

Contreras

Shoshani

2004

Physiological Reviews

151

100

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Transporting epithelia posed formidable conundrums right from the moment that Du Bois Raymond discovered their asymmetric behavior, a century and a half ago. It took a century and a half to start unraveling the mechanisms of occluding junctions and polarity, but we now face another puzzle: lest its cells died in minutes, the first high metazoa (i.e., higher than a sponge) needed a transporting epithelium, but a transporting epithelium is an incredibly improbable combination of occluding junctions and cell polarity. How could these coincide in the same individual organism and within minutes? We review occluding junctions (tight and septate) as well as the polarized distribution of Na+-K+-ATPase both at the molecular and the cell level. Junctions and polarity depend on hosts of molecular species and cellular processes, which are briefly reviewed whenever they are suspected to have played a role in the dawn of epithelia and metazoan. We come to the conclusion that most of the molecules needed were already present in early protozoan and discuss a few plausible alternatives to solve the riddle described above.

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Section: The ␥-Subunitmentioning

confidence: 99%

Cell Adhesion, Polarity, and Epithelia in the Dawn of Metazoans

Cereijido

Contreras

Shoshani

2004

Physiological Reviews

151

100

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“…Known as the ␥ subunit, it is not present in all tissues, and its role in the Na,K-ATPase has long been an enigma (15)(16)(17). As an ancillary subunit it is likely to play a modulatory role.…”

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confidence: 99%

The γ Subunit Modulates Na+ and K+Affinity of the Renal Na,K-ATPase

Arystarkhova

Wetzel

Asinovski

et al. 1999

Journal of Biological Chemistry

184

186

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The Na؉ ,K ؉ -ATPase catalyzes the active transport of ions. It has two necessary subunits, ␣ and ␤, but in kidney it is also associated with a 7.4-kDa protein, the ␥ subunit. Stable transfection was used to determine the effect of ␥ on Na,K-ATPase properties. When isolated from either kidney or transfected cells, ␣␤␥ had lower affinities for both Na ؉ and K ؉ than ␣␤. A post-translational modification of ␥ selectively eliminated the effect on Na ؉ affinity, suggesting three configurations (␣␤, ␣␤␥, and ␣␤␥*) conferring different stable properties to Na,K-ATPase. In the nephron, segment-specific differences in Na ؉ affinity have been reported that cannot be explained by the known ␣ and ␤ subunit isoforms of Na,K-ATPase. Immunofluorescence was used to detect ␥ in rat renal cortex. Cortical ascending limb and some cortical collecting tubules lacked ␥, correlating with higher Na ؉ affinities in those segments reported in the literature. Selective expression in different segments of the nephron is consistent with a modulatory role for the ␥ subunit in renal physiology.

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“…The exact role of the ␥ subunit in Na,K-ATPase function is unknown, although its necessity for both ATPase and transport activity has been questioned experimentally (10)(11)(12). For example, detergent extraction of the ␥ subunit from purified Na,K-ATPase does not affect the ATPase activity of the enzyme (10).…”

mentioning

confidence: 99%

“…For example, detergent extraction of the ␥ subunit from purified Na,K-ATPase does not affect the ATPase activity of the enzyme (10). Moreover, expression studies have demonstrated that the ␣ and ␤ subunits are sufficient for the functional expression of Na,K-ATPase activity and expression of the ␥ subunit with the rat ␣1 and ␤1 subunits in yeast does not affect the affinities of the enzyme for Na ϩ or ouabain (12).…”

mentioning

confidence: 99%

The gamma subunit of the Na,K-ATPase induces cation channel activity

Minor

Sha

Nichols

et al. 1998

Proc. Natl. Acad. Sci. U.S.A.

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The ␥ subunit of the Na,K-ATPase is a hydrophobic protein of approximately 10 kDa. The ␥ subunit was expressed in Sf-9 insect cells and Xenopus oocytes to ascertain its role in Na,K-ATPase function. Immunoblotting has shown that the ␥ subunit is expressed in Sf-9 cells infected with recombinant baculovirus containing the cDNA for the human ␥ subunit. Confocal microscopy demonstrates that the ␥ subunit can be delivered to the plasma membrane of Sf-9 cells independently of the other Na,K-ATPase subunits and that ␥ colocalizes with ␣1 when these proteins are coexpressed. When Sf-9 cells were coinfected with ␣1 and ␥, antibodies to the ␥ subunit were able to coimmunoprecipitate the ␣1 subunit, suggesting that ␥ is able to associate with ␣1. The ␥ subunit is a member of a family of single-pass transmembrane proteins that induces ion f luxes in Xenopus oocytes. Evidence that the ␥ subunit is a functional component was supported by experiments showing ␥-induced cation channel activity when expressed in oocytes and increases in Na ؉ and K ؉ uptake when expressed in Sf-9 cells.

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A proteolipid associated with Na,K-ATPase is not essential for ATPase activity

Cited by 37 publications

References 15 publications

Cell Adhesion, Polarity, and Epithelia in the Dawn of Metazoans

Cell Adhesion, Polarity, and Epithelia in the Dawn of Metazoans

The γ Subunit Modulates Na+ and K+Affinity of the Renal Na,K-ATPase

The gamma subunit of the Na,K-ATPase induces cation channel activity

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