Identification, purification and partial characterization of a 70 kDa inhibitor protein of Na+/K+-ATPase from cytosol of pulmonary artery smooth muscle

Identification, purification and partial characterization of low molecular weight protein inhibitor of Na⁺/K⁺-ATPase from pulmonary artery smooth muscle cells

We have identified a novel endogenous low mol wt. (15.6 kDa) protein inhibitor of Na(+)/K(+)-ATPase in cytosolic fraction of bovine pulmonary artery smooth muscle cells. The inhibitor showed different affinities toward the α₂β₁ and α₁β₁ isozymes of Na(+)/K(+)-ATPase, where α₂ is more sensitive than α₁. The inhibitor interacted reversibly to the E1 site of the enzyme and blocked the phosphorylated intermediate formation. Circular dichroism study suggests that the inhibitor causes an alteration in the confirmation of the enzyme.

Evidence for a 12 kDa "Carrier Protein" for Natriuretic Hormone

The search for the elusive Na-K-ATPase-inhibiting natriuretic hormone continues. In this review, evidence is presented that isolating the carrier protein for natriuretic hormone from hypertensive plasma is a necessary first step before splitting off the final hormone. The carrier protein has a molecular weight of 12 kDa while the final hormone has a molecular weight of 408 Da. Both compounds inhibit Na-K-ATPase but the compound containing the carrier protein predominates. The question has been raised as to whether the carrier protein is in actuality proANF, a 17 kDa protein that can be split between a 14 kDa protein (the presumptive proANF) and the 3 kDa ANF.

Role of phospholemman and the 70 kDa inhibitor protein in regulating Na+/K+ ATPase activity in pulmonary artery smooth muscle cells under U46619 stimulation

Treatment of bovine pulmonary smooth muscle cells with U46619 inhibited the Na(+)/K(+) ATPase activity in two parallel pathways: one of which is mediated via glutathionylation of the pump and the other by augmenting the inhibitory activity of the 70kDa inhibitor protein of Na(+)/K(+) ATPase. Although phospholemman deglutathionylates the pump leading to its activation, the inhibitor is responsible for irreversible inhibition of Na(+)/K(+) ATPase in an isoform specific manner during treatment of the cells with U46619.