Partial purification and ouabain sensitivity of lubrol-extracted sodium-potassium transport adenosine triphosphatases from brain and cardiac tissues

Abstract

Lubrol extracts containing (Na + K)-activated adenosine triphosphatase of specific activity 70–100 μmoles P l/mg of protein/hr were prepared from rat brain microsomal fractions. The enzyme was stable in 0.32 M sucrose containing 1 mM EDTA at pH 6.9 and had properties, regarding optimal concentrations of ATP, Na and K required for maximal activation, similar to those of particulate preparations of the rat brain enzyme. The apparent K m for the enzyme was 5.0 × 10 −4 M and the optimal pH was 6.8. Sucrose density gradient separation further purified the (Na + K)-activated adenosine triphosphatase, but the resulting preparation was not homogeneous, despite high specific activity (400 μmoles P i/mg of protein/hr), and contained at least five protein staining bands on disc gel electrophoresis. Lubrol treatment was effective in extracting the enzyme from cardiac tissue of both rat and guinea pig and appeared to increase the sensitivity of the enzyme to ouabain. Enzymes of cerebral origin from the two species were of equal sensitivity to ouabain. The enzyme extracted by Lubrol treatment from guinea pig heart microsomes was 23 times more sensitive to ouabain than a similar preparation from rat heart.