Alterations in phospholipid-dependent (Na+ +K+)-ATPase activity due to lipid fluidity. Effects of cholesterol and Mg2+

摘要: Abstract The (Na++K+)-activated, Mg2+-dependent ATPase from rabbit kidney outer medulla was prepared in a partially inactivated, soluble depleted of endogenous phospholipids, using deoxycholate. This preparation reactivated 10 to 50-fold by sonicated liposomes phosphatidylserine, but not non-sonicated phosphatidylserine or phosphatidylcholine liposomes. reconstituted enzyme resembled native membrane preparations (Na++K+)-ATPase its pH optimum being around 7.0 showing optimal activity at Mg2+: ATP mol ratios approximately 1 and Km value for 0.4 mM. Arrhenius plots this constant an ratio 1:1 showed discontinuity (sharp change slope) 17 °C, With activation energy (Ea) values 13–15 kcal/mol above temperature 30–35 kcal below it. A further also found 8.0 °C the Ea very high (> 100 kcal/mol). Incresed Mg2+ concentrations excess inhibited abolished discontinuities plots. addition cholesterol reactivation. under these conditions single 20°C 22 68kcal/mol respectively. ouabain-insensitive Mg2+-ATPase normally linear plot with 8 kcal/mol. cholesterol-phosphatidylserine mixed stimulated activity, which now 20 with, however, increased 14 6 below. Kinetic studies that had no significant effect on ATP. Since both are know alter effects fluidity phospholipids result discussed context.