Studies on plasma membranes III. Mg2+-ATPase, (Na+-K+-Mg2+)-ATPase and 5′-nucleotidase activity of plasma membranes isolated from rat liver

• 1.

  1. Plasma membranes have been isolated from rat liver and the ATPase (EC 3.6.1.4), (Na⁺-K⁺)-ATPase and 5′-nucleotidase (EC 3.1.3.5; substrate: AMP) activities of the preparations have been studied.

• 2.

  2. The pH-, Mg²⁺-, temperature- and concentration-dependences and the nucleotide specificity of the ATPase and nucleotidase were established.

• 3.

  3. The ATPase and (Na⁺-K⁺)-ATPase of the isolated plasma membranes hydrolyzed the terminal phosphate bond of ATP. The following effects on the two enzymes were obtained: Ca²⁺, ouabain, cysteine, p-chloromercuribenzoate, Myleran and oligomycin inhibited the (Na⁺-K⁺)-ATPase while having no effect on the ATPase. Ultrasound, oleic acid, vitamin A alcohol and deoxycholate inhibited both ATPases. Bile, deoxycholate (at low concentration), Lubrol-W, deoxycorticosterone acetate and progesterone inhibited ATPase and activated the (Na⁺-K⁺)-ATPase. Activation of the ATPase and inhibition of the (Na⁺-K⁺)-ATPase could be obtained by saponin and preincubation of the membranes at 37°.

• 4.

  4. None of the treatments inhibited the nucleotidase; ultrasound, deoxycholate, saponin and Lubrol-W activated the enzyme.

• 5.

  5. The results are discussed in regard to the relation between membrane structure and enzymic function.