BINDING OF SUGARS TO DNA - AN NMR-STUDY OF D-FRUCTOSE

The major tautomers of D-fructose in water are the beta-pyranose and beta-furanose forms, the former predominating. NMR studies have shown that when aqueous DNA is added, there is a shift in the beta-pyranose half-arrow-right-over-half-arrow-left beta-furanose equilibrium, the latter form being favoured. It is suggested that this is caused by weak, preferential binding of the beta-furanose form to DNA. This is supported by computer modelling, which shows that for the former, only two hydrogen bonds can be formed between sugar O-H groups and phosphate units, whereas three good bonds can be formed with the latter. Studies of the O-H-1 resonances of the anomeric groups of the two forms confirm this change in equilibrium. In addition this feature for the beta-furanose form shifts to low-field without significant broadening. This indicates that strong hydrogen bonding to DNA occurs, but that the equilibrium is very rapid giving fast averaging of the NMR signals.