Golgi membranes from liver express an ATPase with femtomolar copper affinity, inhibited by cAMP-dependent protein kinase

Abstract

Copper-stimulated P-type ATPases are essential in the fine-tuning of intracellular copper. In the present work we characterized a copper-dependent ATPase hydrolysis in a native Golgi-enriched preparation from liver and investigated its modulation by cyclic AMP-dependent protein kinase (PKA). The very high-affinity Atp7b copper pump presented here shows a K0.5 for free copper of 2.5×10−17M in bathocuproine disulfonate/copper buffer and ATP hydrolysis was inhibited 50% upon stimulation of PKA pathway, using forskolin, cAMP or cholera toxin. Incubation with PKA inhibitor (PKAi5–24 peptide) raises Cu(I)-ATPase activity by 50%. Addition of purified PKA α-catalytic subunit increases K0.5 for free copper (6.2×10−17M) without modification in the affinity for ATP in the low-affinity range of the substrate curve (∼1mM). The Hill coefficient for free copper activation also remains unchanged if exogenous PKA is added (2.7 and 2.3 in the absence and presence of PKA, respectively). The results demonstrate that this high-affinity copper pump in its natural environment is a target of the liver PKA pathway, being regulatory phosphorylation able to influence both turnover rate and ion affinity.