Effect of H2O2 on Na,K-ATPase.

Na,K-ATPase is a member of the P-type ATPase family, which transforms the energy of ATP to the transmembrane Na/K gradient that is used to create membrane potential, support the excitability of neurons and myocytes, control pH, and transport substances. The regulation of the Na,K-ATPase function by physiological regulators also comprises a central role in the adaptation of organisms to different conditions. H₂O₂ is one of the main signaling molecules in redox metabolism and plays important function in cellular physiology. H₂O₂ also regulates signaling pathways via the specific oxidation of proteins harboring redox-sensitive moieties, like metal centers or cysteine residues, which control their activity. The Na,K-ATPase is redox-sensitive with an "optimal redox potential range," where the reactive oxygen species (ROS), levels beyond this "optimal range" are responsible for enzyme inhibition. Thus reactive oxygen species manifest a hermetic effect, which is expressed by biphasic action; stimulation by low doses and inhibition by high doses. This study was aimed to reveal redox-sensitivity of brain synaptic membrane fractions Na,K-ATPase via H₂O₂ effects. Different concentrations of H₂O₂ change the kinetic parameters of the enzyme system for MgATP complex, Na⁺, and K⁺ differently. Moreover, H₂O₂ changes p-chloromercuribenzoic acids (PCMB) affinity. H₂O₂ targets thiols of the Na,K-ATPase - low and high concentrations of H₂O₂ change the oxidative state of thiolate (S-) from Cys differently, resulting in the corresponding activation or inhibition of the enzyme. Targeting thiols of the Na,K-ATPase tunes the activity of the Na,K-ATPase to the cellular demands and sustains the enzyme activity at the "optimal" level.