Abstract
Both 1,N6-etheno-AMP and 1,N6-etheno-2''-deoxy-AMP bind at the AMP site of phosphorylase b (1,4-.alpha.-D-glucan:orthophosphate .alpha.-glucosyltransferase, EC 2.4.1.1). Etheno-AMP induces the same activation as AMP, about 30-fold higher than the activation induced by etheno-dAMP. The fluorescence of etheno-AMP and etheno-dAMP is associated with the base moiety; when free is solution, the 2 derivatives have identical fluorescence properties. When bound to phosphorylase, the fluorescence of etheno-AMP is quenched more efficiently than the fluorescence of etheno-dAMP. This difference between the fluorescence properties of the bound nucleotides suggests that a modification in the ribose ring affects the position of the adenine in the AMP site of phosphorylase b. The observed quenching may be due to a stacking interaction between an aromatic residue and the base moiety of the bound nucleotide.