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

The influence of various organic cosolvents on the stability and activity of the β-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 Me 2SO 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). Graphic