Abstract
Na,K-ATPase and H,K-ATPase are the only members of the P-type ATPases in which a glycosylated beta-subunit is part of the purified active enzyme. In this study, we have followed the synthesis and the posttranslational processing of the beta-subunit of H,K-ATPase (beta HK) in Xenopus oocytes injected with beta HK cRNA and have tested whether it can act as a surrogate for the beta-subunit of Na,K-ATPase (beta NaK) to support the functional expression of Na,K-pumps. In Xenopus oocytes, beta HK is processed from an Endo H-sensitive 51-kDa coreglycosylated form to an Endo H-resistant 71-kDa fully glycosylated form. Similar to beta NaK, beta HK can stabilize and increase the trypsin resistance of alpha-subunits of Na,K-ATPase (alpha NaK). Finally, expression of beta HK together with alpha NaK leads to an increased number of ouabain binding sites at the plasma membrane accompanied by an increased Rb+ uptake and Na,K-pump current. Our data suggest that beta HK, similar to beta NaK, can assemble to alpha NaK, support the structural maturation and the intracellular transport of catalytic alpha NaK, and ultimately form active alpha NaK-beta HK complexes with Na,K-pump transport properties.
Highlights
From the Slnstitut de Pharmacologie et de Tonicologie de l’Uniuersit6, CH-1005 Lausanne, Switzerland, §Department of Physiology and Medicine, UCLA, Los Angeles, California 90073, and $Departmenotf Molecular and Cell Biology, Life Sciences Addition, University of a Xenopus neurula library
Subunit is part of the purified active enzyme. In this Nothing is known on the regulatory role of the P-subunit study, we have followed the synthesis and the post- in the catalytic cycle of the enzymes, but recent experimental translational processing of the &subunit of H,K-ATP- evidence obtained for Na,K-ATPase clearly shows that conase (BHK) in Xenopus oocytes injected with BHK cRNA comitant synthesis of aNaK and PNaK is obligatory for the and have tested whether it can act as a surrogate for expression of functional Na,K-pumps at the plasma memthe &subunit of Na,K-ATPase (BNaK) to support the functional expression of Na,K-pumps
We show that in cRNA-injected oocytes, PHK can act as ber of ouabain binding sites at the plasma membrane a surrogate for PNaK in being able to support the structural accompanied by an increased Rb’ uptake and Na,K- maturation of the newly synthesized aNaK, its transport to pump current
Summary
From the Slnstitut de Pharmacologie et de Tonicologie de l’Uniuersit6, CH-1005 Lausanne, Switzerland, §Department of Physiology and Medicine, UCLA, Los Angeles, California 90073, and $Departmenotf Molecular and Cell Biology, Life Sciences Addition, University of a Xenopus neurula library (for review,seeRef. 7).
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