title: Enhancement of enzyme activity in supercritical carbon dioxide via changes in acid-base conditions.
abstract: Enzyme performance is often impaired in supercritical carbon dioxide. We were able to enhance enzyme activity in this medium via changes in acid-base conditions by using ion-exchange materials (solid H(+)/Na(+) buffer pairs and a zeolite), which were selected on the basis of the response of an organosoluble acid-base indicator. The concentration of ion-exchange materials had an important effect on the catalytic activity of subtilisin Carlsberg cross-linked enzyme crystals (CLECs), and this was related to the protonation and hydration states of the enzyme. The buffer Na(2)CO(3)/NaHCO(3) gave the highest enhancement in enzyme activity (by a factor of 54), probably as a result of its high basicity and capacity to counteract the deleterious effect of carbonic acid to a greater extent than the other materials tested.
authors.affiliation: REQUIMTE/CQFB, Departamento de Química, FCT, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal. nharper_pt@yahoo.co.uk
authors.forename: Neil
authors.initials: N
authors.lastname: Harper
authors.forename: Susana
authors.initials: S
authors.lastname: Barreiros
mesh_terms: D000143:Acids; D000468:Alkalies; D002021:Buffers; D002245:Carbon Dioxide; D002384:Catalysis; D004798:Enzymes / Q000737:chemistry*; D007474:Ion Exchange; D020860:Subtilisin / Q000737:chemistry
chemical_list: D000143:Acids; D000468:Alkalies; D002021:Buffers; D004798:Enzymes; D002245:Carbon Dioxide; D020860:Subtilisin