Effect of organic cosolvents on the stability and activity of the beta-1,4-galactosyltransferase from bovine colostrum.

The influence of various organic cosolvents on the stability and activity of the beta-1,4-galactosyltransferase from bovine colostrum (GalT) and of its ancillary enzyme UDP-galactose-4'-epimerase has been investigated using the glucosylated alkaloid colchicoside (1) as a model substrate. It has been found that some cosolvents, such as Me2SO and MeOH, can be used up to 20% v/v without any influence on the performance of these enzymes, while others, such as tetrahydrofuran, rapidly inactivated GalT at concentrations as low as 5% v/v. These results have been exploited for the galactosylation of the poorly water soluble coumarinic glucoside fraxin (2).