Effects of metal salts on the structure and activity of α-chymotrypsin in ethanol water

The catalytic activity and circular dichroic (CD) spectra of alpha-chymotrypsin (CT) were measured in ethanol/water (95/5, v/v) solution containing small amounts of metal salts. Although the catalytic activity of CT increased upon the addition of all the metal salts used, the magnitude of activity increase was different for different metal salts. Especially, calcium acetate accelerated the transesterification of amino acid up to 6 fold at 100 mu M. The secondary and tertiary structures of CT were also changed by metal salts, as studied by CD measurements. The effects of metal salts on the stability of CT in ethanol/water were also studied, and it was found that the residual activity of CT after 7 days in ethanol/water in the presence of Ca(OCOCH3)(2) was about 20% of the initial activity. The change in activity was closely correlated with the change in the mean residue ellipticity of CT at 208 or 230 nm.