부산대학교 도서관

Na,K-ATPase activity must be finely controlled to meet the constantly changing physiological demands and to avoid destabilization of body homeostasis. Recent experimental evidence suggests that certain regulatory mechanisms are closely linked to the multisubunit structure of the Na,K-pump molecule. Na,K-ATPase is composed of a catalytic α and a glycoprotein β subunit and sometimes of a third component, the γ subunit. The β subunit is a fundamental element of Na,K-ATPase in that its assembly in the ER is required for the structural and functional maturation of the catalytic α subunit and in consequence the β subunit controls the expression of functional pumps at the cell surface. Furthermore, β subunits influence the transport properties of the mature catalytic α subunits. Distinct interaction sites mediate the two functions of the β subunit. Recently, we have started to characterize the γ subunit, the functional role of which is yet not known. Immuno-radiolabeling of epitope-tagged γ subunits expressed in Xenopus oocytes shows that the γ subunit is a type I membrane protein which specifically associates only with Na,K-ATPase but not with other oligomeric P-type ATPases. The γ peptide does not influence the formation or the cell surface expression of functional α-β complexes. On the other hand, the γ peptide itself needs association with Na,K-ATPase to be stably expressed and to be efficiently transported to the plasma membrane. Finally, the γ subunit can modulate the K activation of Na,K-pumps. In conclusion, processes such as subunit assembly or the subunit composition of the cell surface expressed Na,K-pumps appear to cooperate with hormones in the control of the expression and the activity of Na,K-ATPase. [ABSTRACT FROM AUTHOR]