Thermal inactivation of membrane-bound acid phosphatase. The residual activity was determined by the addition of 50-μL aliquots to 50 mM acetate buffer, pH 6.0, containing 1 mM PNPP, in a final volume of 1.0 ml. Values are the mean of triplicates determinations that differed by less than 5% variation. (●) 50°C; (▲) 70°C; (■) 60°C; (□) 65°C; (○) 55°C. Inset: Arrhenius plot for the above data.