Characterization of the the (Na + +K+)-ATPase in a membranous preparation from the optic ganglion of the squid (Loligo pealei).
(1) A membrane fraction enriched in (Na+ +K+)-ATPase (EC 3.6.1.3) was obtained from optic ganglia of the squid (Loligo pealei) by density gradient fractionation of membranes followed by treatment with either SDS or Brij-58. The resulting membrane had an (Na+ +K+)-ATPase specific activity of approx. 2 units/mg and was greater than 95% ouabain-sensitive. (2) The (Na+ +K+)-ATPase had a Km for ATP of 0.42 +/- 0.04 mM and a pH optimum of 7.0. It was inhibited by ouabain with a Ki of 0.32 +/- 0.04 microM. (3) Optimum monovalent cation concentrations were: 240 mM NaCl, 60 mM KCl, tested with NaCl + KCl = 300 mM. (4) The Mg2+ dependence of hydrolysis varied with the absolute ATP concentration. At 3 mM ATP, the Km for Mg2+ was 0.86 +/- 0.10 mM, and at 6 mM ATP, the Km was 1.86 +/- 0.44 mM. High levels of Mg2+ caused inhibition of hydrolysis. (5) The interactions of Na+ and K+ were examined over a range of conditions. K+ levels caused modulations in the Na+ dependence in the range of 1-150 mM. (6) The (Na+ +K+)-ATPase prepared from squid optic ganglion displays properties similar to those of the sodium pump in injected nerves.
D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D049832:Decapodiformes; D005726:Ganglia, Parasympathetic / Q000201:enzymology*; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology; D010042:Ouabain / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D012965:Sodium Chloride / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism*
D012965:Sodium Chloride; D010042:Ouabain; D011189:Potassium Chloride; D000254:Sodium-Potassium-Exchanging ATPase