title: Free fatty acids and (Na+,K+)-ATPase: effects on cation regulation, enzyme conformation, and interactions with ethanol.
abstract: Effects of free fatty acids on parameters of (Na+,K+)-ATPase regulation related to enzyme conformation were examined. Sensitivity to inhibition by free fatty acid increased as the number of double bonds increased. Free fatty acids reduced affinity for K+ or Na+ at their regulatory sites without altering apparent K+ affinity at its high-affinity site, and increased apparent affinity for ATP. The apparent E2/E1 ratio and apparent delta H and delta S for the E1-E2 transition were reduced by fatty acid. High K+ or low temperature reduced the sensitivity of enzyme to inhibition by free fatty acid. In the presence of low K+, arachidonic acid potentiated inhibition of phosphatase activity by ethanol. Arachidonic acid alone had little effect on the rate of ouabain binding, but accelerated ouabain binding in the presence of K+. These data suggest that fatty acids alter (Na+,K+)-ATPase by preventing the univalent cation-mediated transition to E2, the K+-sensitive form of enzyme. (Na+,K+)-ATPase could potentially be influenced in vivo by free fatty acids released by phospholipases or during hypoxia, or by changes in membrane lipid saturation.
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000378:metabolism; D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000494:pharmacology; D001665:Binding Sites / Q000187:drug effects; D001667:Binding, Competitive; D001921:Brain / Q000201:enzymology; D002412:Cations / Q000502:physiology; D002417:Cattle; D000431:Ethanol / Q000494:pharmacology*; D005230:Fatty Acids, Nonesterified / Q000502:physiology*; D008560:Membrane Fluidity / Q000187:drug effects; D010042:Ouabain / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D011487:Protein Conformation; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013696:Temperature
chemical_list: D001095:Arachidonic Acids; D002412:Cations; D005230:Fatty Acids, Nonesterified; D016718:Arachidonic Acid; D000431:Ethanol; D010042:Ouabain; D009597:4-Nitrophenylphosphatase; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium