Studies on the thermal inactivation of immobilized enzymes

Convenience of immobilized Bacillus licheniformis alpha-amylase as time-temperature-integrator (TTI)

For the immobilization of Bacillus licheniformis alpha-amylase to porous glass beads, the performances of three possible linking agents, glutaric dialdehyde, benzoquinone and s-trichlorotriazine were assessed in respect of the protein yield, the enzymic activity and the thermostability of the immobilized enzyme. These three properties are to be evaluated in view of the possible use of the enzyme preparations as time-temperature-integrators (TTIs) for assessing the severity of heat pasteurization or sterilization processes of food or pharmaceuticals. All three linkers improved the enzyme's resistance to irreversible heat inactivation to a similar extent and in each case biphasic inactivation kinetics were observed, whereas the dissolved B. licheniformis alpha-amylase showed a simple first order decay. The immobilization yield, measured as protein per carrier weight, did not differ markedly for the three linkers, although the enzymic activity of the glutaric dialdehyde-linked enzyme was lower than that of the benzoquinone- and s-trichlorotriazine-linked preparations.

Spacer effects on enzymatic activity of papain immobilized onto porous chitosan beads

Papain was covalently immobilized onto the surface of porous chitosan beads without or with spacers of different lengths. The relative activity of the immobilized papain was found to be high toward a small ester substrate, N-benzyl-L-arginine ethyl ester (BAEE), but rather low toward casein, a high molecular weight substrate. Papain immobilized with spacer gave an almost constant activity, in marked contrast with the immobilized papain without spacer, whose activity monotonously decreased with decreasing surface concentration. The relative activity of the immobilized papain for hydrolysis of a high molecular weight substrate greatly depended on the length of the spacer. The pH, thermal and storage stabilities of the immobilized papain were higher than those of the free one, and ths papain immobilized directly to the chitosan beads' surface without any spacer gave a higher stability than those immobilized with spacer. The spacer's effect on the activity could be explained in terms of mobility of the immobilized papain molecule.

Synthesis of carboxylated poly(NIPAAm) oligomers and their application to form thermo-reversible polymer-enzyme conjugates

A thermo-reversible poly(N-isopropylacrylamide) poly(NIPAAm) oligomer with a carboxyl functional end group has been synthesized by radical polymerization using beta-mercaptopropionic acid as a chain transfer reagent. This polymer has been conjugated to an enzyme, beta-D-glucosidase, to form a thermo-reversible water soluble-insoluble polymer-enzyme conjugate. This conjugate can be used for separation, recovery and recycle of an enzyme simply by applying small temperature changes to the reaction medium. In contrast to the random polymer-enzyme conjugates reported in the literature, in this study the enzyme is coupled to each polymer chain by a single end attachment. These preliminary studies show that the conjugated enzyme exhibits very high retention of activity (> 90%) compared to the native enzyme and shows improved thermal stability.

Kinetics and mechanisms of reactions catalysed by immobilized lipases

This review focuses on the kinetics and mechanisms of reactions catalysed by immobilized lipases. The effects of pH, temperature, and various substances on the catalytic properties of immobilized lipases and on the processes by which they are deactivated are reviewed and discussed.