glycosyltransferases are carbohydrate - active enzymes with essential roles in numerous important biological processes . 
 we have developed a novel donor analogue for galactosyltransferases which locks a representative target enzyme in a catalytically inactive conformation , thus almost completely abolishing sugar transfer . 
 results with other galactosyltransferases suggest that this novel and unique mode of glycosyltransferase inhibition is , very likely , generally applicable to other members of this very important enzyme family also .