Model and simulation of Na+/K+ pump phosphorylation in the presence of palytoxin

The ATP hydrolysis reactions responsible for the Na+/K+-ATPase phosphorylation, according to recent experimental evidences, also occur for the PTX–Na+/K+ pump complex. Moreover, it has been demonstrated that PTX interferes with the enzymes phosphorylation status. However, the reactions involved in the PTX–Na+/K+ pump complex phosphorylation are not very well established yet. This work aims at proposing a reaction model for PTX–Na+/K+ pump complex, with similar structure to the Albers–Post model, to contribute to elucidate the PTX effect over Na+/K+-ATPase phosphorylation and dephosphorylation. Computational simulations with the proposed model support several hypotheses and also suggest: (i) phosphorylation promotes an increase of the open probability of induced channels; (ii) PTX reduces the Na+/K+ pump phosphorylation rate; (iii) PTX may cause conformational changes to substates where the Na+/K+-ATPase may not be phosphorylated; (iv) PTX can bind to substates of the two principal states E1 and E2, with highest affinity to phosphorylated enzymes and with ATP bound to its low-affinity sites. The proposed model also allows previewing the behavior of the PTX–pump complex substates for different levels of intracellular ATP concentrations.