Wellington Sabino Adriano

Improving the Properties of Chitosan as Support for the Covalent Multipoint Immobilization of Chymotrypsin

Changing gel structure and immobilization conditions led to a significant improvement in the covalent multipoint attachment of chymotrypsin on chitosan. The use of sodium alginate, gelatin, or kappa-carrageenan, activation with glutaraldehyde, glycidol, or epichlorohydrin, and addition of microorganisms followed by cellular lysis allowed the modification of the gel structure. Immobilization yields, recovered activities, and stabilization factors at 55 and 65 degrees C were evaluated. Enzyme immobilization for 72 h at pH 10.05, 25 degrees C and reduction with NaBH 4 in chitosan 2.5%-carrageenan 2.5%, with addition of S. cerevisiae 5% and activation with epichlorohydrin led to the best derivative, which was 9900-fold more stable than the soluble enzyme. This support allowed an enzyme load up to 40 mg chymotrypsin x g gel (-1). The number of covalent bonds, formed by active groups in the support and lysine residues of the enzyme, can explain the obtained results. SEM images of the gel structures corroborate these conclusions.

Stabilization of penicillin G acylase by immobilization on glutaraldehyde-activated chitosan

Abstract - The objective of this work was to study enzyme immobilization on chitosan activated with glutaraldehyde, aiming to produce a cheap biocatalyst. Two different immobilization strategies were studied: one-point and multipoint covalent attachment to the solid matrix. The multipoint covalent attachment derivative had an 82% immobilization yield. It was4.9-fold more stable than the free enzyme at 50°C and 4.5-fold more stable than soluble enzyme at pH 10.0. The one-point derivativehad an 85% immobilization yield. It was 2.7-fold more stable than the free enzyme at 50°C and 3.8-fold more stable than soluble PGA at pH 10.0. Results indicated that chitosan can be loaded with PGA above 330 IU/g. Intraparticle diffusive effects, however,limited hydrolysis of penicillin G catalyzed by those derivatives at 37°C and 25°C. Operational stability assays were performed and the multipoint derivative exhibited a half-life of 40 hours. Keywords : Stabilization of enzymes; Penicillin G acylase; Chitosan and immobilization of enzymes.