A one-pot glycosylation reaction is disclosed in which a mannosyl (Man) group is enzymatically transferred to an acceptor molecule. The starting glycoside is a mannosyl 1-phosphate that is enzymatically converted to its GDP derivative via UTP and a pyrophorylase. The formed GDP derivative is used in the enzyme-catalyzed glycosyl transfer. That enzyme-catalyzed glycosyl transfer to an acceptor releases GDP that is enzymatically converted to GTP for further conversion of mannosyl 1-phosphate into its GDP derivative. Also disclosed are a recombinant 1,2-mannosyltransferase that is enzymatically active, is dispersible in an aqueous reaction medium, and free of the transmembrane portion of the native enzyme, as well as DNA encoding that transferase, an expression vector containing exogenous DNA that encodes that enzyme and E. coli cells containing that vector.