ATP binding site in the plant ADP-glucose pyrophosphorylase large subunit

The ATP binding region in the catalytically inactive large subunit (LS) of the potato tuber ADP-glucose pyrophosphorylase was identified and investigated. Mutations at the ATP binding significantly affected not only the apparent affinities for ATP and Glc-1-P, and catalytic rate but also in many instances, sensitivity to 3-phosphoglycerate. The catalytic rates of the LS mutant enzymes correlated most strongly with changes in the affinity toward ATP, a relationship substantiated by photoaffinity labeling studies with azido-ATP analog. These results indicate that the LS, although catalytically defective, interacts cooperatively with the catalytic small subunit in binding substrates and effectors and, in turn, influencing net catalysis. (c) 2006 Published by Elsevier B.V. on behalf of the Federation of European Biochemical Societies.