Enzymatic activity of alkaline phosphatase adsorbed on dimyristoylphosphatidic acid Langmuir-Blodgett films

The kinetics and the adsorption isotherms of the surfactant-solubilized alkaline phosphatase from rat osseous plate adsorbed by dip-coating on dimyristoyl phosphatidic acid (DMPA) Langmuir-Blodgett (LB) films were studied. The phosphomonohydrolase activity of the enzyme on the LB film was estimated by the hydrolysis of p-nitrophenylphosphate (PNPP). Films prepared from solutions containing 0.30 mug ml(-1) of protein showed maximum activity for the supported enzyme above the critical micellar concentration of the non-ionic surfactant (polyoxyethylene-9-lauryl ether) used for enzyme solubilization. The surface density of the enzyme on DMPA LB films was determined from quartz crystal microbalance measurements. A consistent explanation concerning the maximum enzymatic activity is supported by data of surface tension for the mixed non-ionic surfactant -enzyme system. (C) 2002 Elsevier Science B.V. All rights reserved.