Kinetics of Na+-, K+-ATPase Inhibition by an Endogenous Modulator (II-A) |
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Authors: | Reinés A. Peña C. Rodríguez de Lores Arnaiz G. |
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Affiliation: | (1) Instituto de Biología Celular y Neurociencias Prof. Eduardo De Robertis, PROBICENE-CONICET, Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155, 1121 Buenos Aires, Argentina;(2) IQUIFIB, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, 1113 Buenos Aires, Argentina;(3) Instituto de Biología Celular y Neurociencias Prof. Eduardo De Robertis, PROBICENE-CONICET, Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155, 1121 Buenos Aires, Argentina |
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Abstract: | We have previously reported the isolation by gel filtration and anionic exchange HPLC of two brain Na+, K+-ATPase inhibitors, II-A and II-E, and kinetics of enzyme interaction with the latter. In the present study we evaluated the kinetics of synaptosomal membrane Na+, K+-ATPase with II-A and found that inhibitory activity was independent of ATP (2–8 mM), Na+ (3.1–100 mM), or K+ (2.5–40 mM) concentration. Hanes-Woolf plots showed that II-A decreases Vmax in all cases; KM value decreased for ATP but remained unaltered for Na+ and K+, indicating respectively uncompetitive and noncompetitive interaction. However, II-A became a stimulator at 0.3 mM K+ concentration. It is postulated that brain endogenous factor II-A may behave as a sodium pump modulator at the synaptic region, an action which depends on K+ concentration. |
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Keywords: | Synaptosomal membranes Na+, K+-ATPase enzyme inhibitor endogenous modulator brain soluble factor |
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