ADSORPTION, ACTIVITIES AND KINETICS OF ACID PHOSPHATASE AS INFLUENCED BY MONTMORILLONITE WITH DIFFERENT INTERLAYER MATERIAL

Abstract

The effects of montmorillonite (Osage, Wyoming) with different interlayers on the adsorption, activities, and kinetic properties of acid phosphatase were examined. Hydroxy polymers of aluminum or chromium (200 cmol kg−1 clay) were intercalated in montmorillonite in the absence or presence of citric acid (citrate/Al or Cr = 0.1 and 0.5). The activities of acid phosphatase in the presence of different amounts of clay at three pH values (5.0, 5.5, and 6.0) were determined, and the Michaelis-Menten kinetic parameters were calculated. The amount of enzyme adsorbed by interlayered montmorillonite was considerably lower than that by pure montmorillonite and increased as the citrate/Al or Cr ratio increased. The type of interlayer (Al or Cr) influenced the ease with which enzymes could be removed by washing. Complete adsorption of the enzyme led to the formation of clay-enzyme complexes, which had lower activities than the free enzyme. The order of activity of enzymes following adsorption was Cr-montmorillonite > Al-montmorillonite > montmorillonite. The effect of citrate on enzyme activity in the clay-enzyme complexes was significant only at the higher ratio. Factors that caused a reduction in enzyme activity were adsorption by clay, amount of clay, and increase in pH. These effects were modified by the type of interlayers (Al or Cr), the citrate/Al or Cr molar ratio, and the strength of adsorption. In the presence of clay, the Michaelis-Menten affinity constant (Km), increased, whereas the maximum enzyme reaction velocity (Vmax), decreased compared with the free enzyme. The change of the enzyme kinetics by Al- and Cr-interlayered montmorillonite can be described as partial noncompetitive inhibition.