The inhibitory activity of a brain extract on synaptosomal Na+, K+-ATPase is sensitive to carboxypeptidase A and to chelating agents.
In the present study some properties of an inhibitory extract of synaptosomal membrane Na+, K+-ATPase were investigated. This extract (peak II) was prepared by gel filtration in Sephadex G-50 of a soluble fraction of the rat cerebral cortex. Ultrafiltration of peak II through Amicon membranes indicated that the inhibitor has a low MW (less than 1000). The inhibitory activity was not modified by heating in neutral pH at 95 degrees C for 20 min but it was destroyed by charring in acid pH at 200 degrees C for 120 min. The inhibitory activity decreased by incubation of peak II with carboxypeptidase A. These findings suggest that the factor responsible for the inhibition of Na+, K+-ATPase activity is probably a polypeptide. On the other hand, the inhibition was reverted by the chelators EDTA and EGTA, indicating the participation of an ionic compound as well. The increase of Mg2+ concentration during the enzyme assay did not increase the inhibition, indicating that the ion involved might not be vanadate. It is suggested that both a polypeptide and an ionic compound coparticipate in the inhibitory effect of peak II on Na+, K+-ATPase activity.
Antonelli de Gómez de Lima
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Instituto de Biología Celular, Facultad de Medicina, Universidad de Buenos Aires.
Rodríquez de Lores Arnaiz
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D000818:Animals; D001923:Brain Chemistry; D002268:Carboxypeptidases / Q000494:pharmacology*; D043422:Carboxypeptidases A; D002614:Chelating Agents / Q000494:pharmacology*; D004492:Edetic Acid / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013574:Synaptosomes / Q000187:drug effects / Q000201:enzymology*; D014020:Tissue Extracts / Q000494:pharmacology*
D002614:Chelating Agents; D004791:Enzyme Inhibitors; D014020:Tissue Extracts; D004533:Egtazic Acid; D004492:Edetic Acid; D002268:Carboxypeptidases; D043422:Carboxypeptidases A; D000254:Sodium-Potassium-Exchanging ATPase