Unexpected Anomeric Acceptor Preference Observed Using dDNP NMR for Transglycosylation Studies of β-Galactosidases

The transglycosylation abilities of beta-galactosidases were investigated using hyperpolarized [U-C-1(3),U-H-2]glucose as an acceptor and o-nitrophenyl beta-galactopyranoside as a donor. Several products were readily observable, and at least in the case when O3 acted as an acceptor, the enzymes showed a clear selectivity toward the beta-anomer of glucose. Additionally, it was possible to determine the relative hydrolysis rates of the formed transglycosylation products, providing information on the selectivity as well. Using this method, the transglycosylation abilities of the enzymes could be studied at a very high temporal resolution as well as with high sensitivity, and due to the relative ease of the setup, this method could be more generally applied to investigate glycosidases.