EFFECTS OF TRITON X-100 AND CONCANAVALIN- A ON THE PROPERTIES OF 5'-NUCLEOTIDASE IN RAT-LIVER AND ADIPOSE PLASMA-MEMBRANES - A ROLE OF THE MEMBRANE-STRUCTURE IN THE REGULATION OF THE ENZYME-ACTIVITY

The kinetic and thermodynamic properties of 5'-nucleotidase (EC 3.1.3. 5) were investigated in rat liver and adipose plasma membranes (PM) af ter their structural modification with nonionic detergent Triton X-100 (TX-100) or lectin Concanavalin A (Con-A). The apparent Km value of 5 '-nucleotidase decreased after PM treatment with subsolubilizing TX-10 0 concentrations (0.005-0.015%) and then tended to grow at higher TX c oncentrations (0,03-0,05%). The treatment of PM with Con-A resulted in the non-competitive inhibition of 5'-nucleotidase in a dose-dependent manner. The Arrhenius plot of the 5'-nucleotidase activity in the con trol PM exhibited, a single well defined break at about 28-31 degrees C with a lower activation energy at the upper slope of the graph. The shape of the observed Arrhenius graphs and the thermodynamic parameter s of 5'-nucleotidase were specifically modified upon the PM treatment with increasing concentrations of TX-100 or Con-A. It was suggested th at the functional activity of 5'-nucleotidase and its conformation wit hin the membrane matrix may be directly regulated by the structural st ates of the enzyme specific microenvironment and of the membrane lipid bilayer. Moreover, the existance of the spatial and/ (or) composition al optima for the relationship between the enzyme molecule and its lip id surrounding may be reasonably supposed.