Acid phosphatase interactions with organo-mineral complexes: influence on catalytic activity

Abstract

The influence of montmorillonite intercalated with representatives of three major classes of biological molecules-lysine (amino acid), α–glucose (carbohydrate) and rhamnolipid (lipid) on the catalytic activity of acid phosphatase was investigated. In comparison to pure clay, the presence of the organic intercalates preserves residual activity at extreme pH values of 3 and 11 and temperatures as low as 10 °C. Thermodynamic parameters of free energy, enthalpy and entropy, suggest that catalytic activity on the lysine and rhamnolipid intercalated surfaces is more spontaneous and favorable than that of pure clay. Michaelis-constants (Km values) and maximum reaction velocities (Vmax values) were determined and confirmed the enhancement of activity on the organo-mineral surfaces. The catalytic reaction product was measured as a function of time and the data fitted to equations describing the behavior of first and second order rates of reaction. All processes apart from the glucose-intercalated clay (second order) could be described by first order reactions. Catalytic activity was generally less on the glucose-mineral surface compared to the other organo-mineral surfaces and the pure clay. However, when all surfaces were saturated with acid phosphatase the glucose complex exhibited the highest level of catalytic activity.