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Abstract

The pectin esterases from tomatoes and Aspergillus foetidus were immobilized by covalent attachment to CNBr-activated Sepharose 4B and by adsorption to polyethylene terephthalate and the properties of the immobilized enzymes were compared. The relative activity of tomato pectin esterase after the immobilization to both supports was almost 7%, whereas the activity of A. foetidus pectin esterase covalently immobilized on CNBr-activated Sepharose 4B was close to 11.5% and a value of almost 23% was measured with the enzyme immobilized by adsorption to polyethylene terephthalate. The pH-optima of both pectin esterases were unchanged after their immobilization, their temperature stability and temperature optimum of activity, however, significantly increased. The differences in the action of free and immobilized pectin esterases were also observed when the final esterification degree of the substrate was compared: the immobilized enzymes, unlike the free pectin esterases, did not act on pectin showing a higher esterification degree. An increase in K_m.app which was 5-fold for the tomato pectin esterase and 4-7-fold for the A. foetidus pectin esterase was observed after the immobilization. The immobilization of both pectin esterases on Enzacryl AA which had been activated by diazotization resulted in complete loss of activity; this indicates the role of the residues of tyrosine (and histidine, resp.) in the catalytic action of these enzymes, which has been observed in earlier experiments.