Circular dichroism measurements, using synchrotron radiation, showed that the secondary structure of Candida antarctica lipase does not differ significantly when changed from an aqueous to organic solvent environment. Thus, we may conclude that a major conformational change is not the reason for the different product produced by the enzyme when used in organic solvent. Significant changes in the lipase's alpha-helix content were found at the extremes of pH 4.2 and 9.0; this is in keeping with the permanent loss of activity of the enzyme at such a pH. (C) 2004 Elsevier Inc. All rights reserved.