COMPARISON OF MACROMOLECULAR AND MOLECULAR EFFECTS OF COSOLVENTS ON THE CATALYTIC BEHAVIOR OF SOYBEAN LIPOXYGENASE-1

The addition of sugars and polyols to the reaction medium of soybean l ipoxygenase-l confers it properties analogous to those of cytoplasm an d can modulate the catalytic behaviour of the enzyme. In such non conv entional media, changes can be observed at two different levels: addit ives exert macroscopic effects on physico-chemical and/or thermodynami c parameters of the reaction medium i.e., water activity, viscosity, s urface tension; cosolvents may also exert effects at the molecular lev el by directly modifying enzyme conformation. Both effects may affect enzyme catalysis, and their relative contribution to the modulation of lipoxygenase-1 activity and specificity has been evaluated. When addi tive concentrations were higher than a threshold of around 35 g additi ve/100 g solution, macromolecular effects limited enzyme catalysis as shown by a diffusion-reaction modelling. Below this value, slight enzy me structural changes were responsible for the observed variations in lipoxygenase behaviour, including activation.