An endogenous factor which interacts with synaptosomal membrane Na+, K(+)-ATPase activation by K+.
In previous papers, the isolation of brain soluble fractions able to modify neuronal Na+, K(+)-ATPase activity has been described. One of those fractions-peak I-stimulates membrane Na+, K(+)-ATPase while another-peak II-inhibits this enzyme activity, and has other ouabain-like properties. In the present study, synaptosomal membrane Na+, K(+)-ATPase was analyzed under several experimental conditions, using ATP or p-nitrophenylphosphate (p-NPP) as substrate, in the absence and presence of cerebral cortex peak II. Peak II inhibited K(+)-p-NPPase activity in a concentration dependent manner. Double reciprocal plots indicated that peak II uncompetitively inhibits K(+)-p-NPPase activity regarding substrate, Mg2+ and K+ concentration. Peak II failed to block the known K(+)-p-NPPase stimulation caused by ATP plus Na+. At various K+ concentrations, percentage K(+)-p-NPPase inhibition by peak II was similar regardless of the ATP plus Na+ presence, indicating lack of correlation with enzyme phosphorylation. Na+, K(+)-ATPase activity was decreased by peak II depending on K+ concentration. It is postulated that the inhibitory factor(s) present in peak II interfere(s) with enzyme activation by K+.
Rodríguez de Lores Arnaiz
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Instituto de Biología Celular, Facultad de Medicina, Universidad de Buenos Aires, Argentina.
D009597:4-Nitrophenylphosphatase / Q000378:metabolism; D000818:Animals; D001685:Biological Factors / Q000502:physiology*; D004789:Enzyme Activation / Q000502:physiology; D005260:Female; D007425:Intracellular Membranes / Q000201:enzymology; D008297:Male; D011188:Potassium / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013574:Synaptosomes / Q000201:enzymology*
D001685:Biological Factors; D009597:4-Nitrophenylphosphatase; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium