ADSORPTION, ACTIVITIES AND KINETICS OF ACID-PHOSPHATASE AS INFLUENCEDBY MONTMORILLONITE WITH DIFFERENT INTERLAYER MATERIAL

The effects of montmorillonite (Osage, Wyoming) with different interla yers on the adsorption, activities, and kinetic properties of acid pho sphatase 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 activ ities 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 Micha elis-Menten kinetic parameters were calculated. The amount of enzyme a dsorbed by interlayered montmorillonite was considerably lower than th at 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 fol lowing adsorption was Cr-montmorillonite > Al-montmorillonite > montmo rillonite. The effect of citrate on enzyme activity in the clay-enzyme complexes was significant only at the higher ratio. Factors that caus ed a reduction in enzyme activity were adsorption by clay, amount of c lay, and increase in pH. These effects were modified by the type of in terlayers (Al or Cr), the citrate/Al or Cr molar ratio, and the streng th of adsorption, In the presence of clay, the Michaelis-Menten affini ty constant (K-m), increased, whereas the maximum enzyme reaction velo city (V-max), decreased compared with the free enzyme. The change of t he enzyme kinetics by Al- and Cr-interlayered montmorillonite can be d escribed as partial noncompetitive inhibition.