Effect of detergents and sodium fluoride on the enzyme activities of the rat liver plasma membrane

The effects of ionic and non-ionic detergents on the absorbance and enzyme activities of the rat liver plasma membrane have been studied. The absorbance (turbidity) versus detergent concentration titration curve was characteristic and non-linear for each detergent. At low detergent concentration (up to 0.025 %) the non-ionic detergents were either more effective or equally effective as the anionic detergents in solubilizing the membrane but at higher detergent concentration (4-10 %), the anionic detergents were more effective. Sodium dodecyl sulfate at o.i % strongly inhibited ATPase (EC 3.6.1.3) and 5′-nucleotidase activities (EC 3.1.3.5) whereas deoxycholate gave a slight stimulation of ATPase and a moderate stimulation of 5′-nucleotidase. Triton X-100 had no effect on ATPase but stimulated 5′-nucleotidase. Lubrol-PX gave a moderate stimulation of both these enzymes. 0.1% sodium dodecyl sulfate stimulated adenylate cyclase (formerly known as adenyl cyclase) activity in crude membranes and in purified membranes prepared either by the method of Neville or the method of Ray. However, NaF-stimulated adenylate cyclase in crude membranes or in membranes prepared by the method of Neville²² but inhibited adenylate cyclase in membranes made by the method of Ray²¹. The effect of sodium dodecyl sulfate and NaF on ATP metabolism by the membrane showed these agents inhibit the conversion of ATP to ADP, AMP and adenosine but the effects are dependent on the concentration of membrane. At low membrane concentration, ATPase is the dominant enzyme but at high membrane concentration 5′-nucleotidase plays an important role in the overall metabolism of ATP. These studies demonstrate a complex interaction of detergents with membrane-bound enzymes and a complex system for nucleotide degradation in the plasma membrane.