INVERTASE (BETA-FRUCTOSIDASE) - EFFECTS OF MONTMORILLONITE, AL-HYDROXIDE AND AL(OH)X-MONTMORILLONITE COMPLEX ON ACTIVITY AND KINETIC-PROPERTIES

The effects of a montmorillonite (M), a non-crystalline aluminium hydroxide (AL) and an Al(OH)x-montmorillonite complex (a montmorillonite partially coated with OH-Al ions; AM) on the adsorption, residual activity and kinetic properties of invertase were determined. In the range of pH 3.0-9.0 the ability of the clay minerals to adsorb protein molecules was in the order M > AM > AL and was influenced by the nature of the buffer solution. Adsorption resulted in a significant reduction of invertase activity (more than 85% at pH 4.65), the extent of which depended on clay mineral (AL > AM > M) and on pH. The free and immobilized enzyme showed maximum activity in the range of pH 4.5-5.5 and both states obeyed Michaelis-Menten kinetics. The V(max) and K(m) values indicated a partial non-competitive inhibition of the clay minerals. Invertase adsorbed on AM and AL was more stable to thermal deactivation than was free enzyme, whereas invertase held on M was much less stable. In contrast, invertase adsorbed on M was more stable to the action of protease than free enzyme or that adsorbed on AM or AL.