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The work was aimed at exploring how chemical modification or noncovalent complexation of enzymes affects their activity and stability. A particular interest is their behaviour in the presence of organic solvents, both while dissolved in aqueous organic mixtures and in suspension in low-water systems. The main enzymes studied have been chymotrypsin and trypsin (of particular interest as catalysts of peptide synthesis), and peroxidase (useful in analysis and waste treatment). Alcohol dehydrogenases and a novel thermostable esterase from Bacillus acidocaldarius were also studied. The main chemical modifications studied are acylation with cyclic anhydrides and reaction with mono- and bi-functional substituted succinimides. Complexation studies have been made with a variety of cationic and anionic polyelectrolytes, including naturally occuring oligoamines.
It has been shown that both covalent modification and complexation by polyelectrolytes can stabilize enzymes against exposure to aqueous-organic mixtures. Various physical methods (especially fluorescence) have been applied to study the mechanisms behind this stabilization. In lower water systems, complexation with polyelectrolytes has been shown to give suspended catalyst particles that are "self-buffered" against undesirable acid base changes. Enzyme-polyelectrolyte complexes can even be active in media with high contents of dimethylformamide, usually a very damaging solvent for enzymes. Various covalent modifications also stabilize enzymes in aqueous-organic mixtures, and other conditions. Modifications that introduce additional charges are usefully combined with polyelectrolyte complexation. Some types of covalent modification significantly affect water adsorption by enzyme powders, and the corresponding dependence of their catalytic activity on the availability of water.
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