Enhancement of Enzyme Activity in Supercritical Carbon Dioxide via Changes in Acid—Base Conditions

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 Na2CO3/ NaHCO3 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.