The N-Terminal Region Is Important for the Allosteric Activation and Inhibition of theEscherichia coliADP-Glucose Pyrophosphorylase

The ADPglucose pyrophosphorylase (EC 2.7.7.27) fromEscherichia coliis allosterically activated by fructose 1,6-bisphosphate and inhibited by AMP. Proteolysis of the enzyme with proteinase K causes loss of activity and generates two peptides, 21 and 28 kDa, from the 49.7-kDa subunit. The presence of ADPglucose, Mg2+, and fructose 1,6-bisphosphate during the incubation with proteinase K protected the enzyme activity and prevented cleavage at sites Met181-Ala182and Phe192-Val193. Proteolysis of the protected enzyme removed 10 to 13 amino acids from the N-terminal and 2 amino acids from the C-terminal. The resulting enzyme was almost independent of the need for fructose 1,6-bisphosphate for maximal activity and insensitive to inhibition by AMP. The apparent affinity for the substrates was similar to that of the fully-activated wild-type enzyme. These data suggest that amino acid residues in the N-terminal portion and possibly the C-terminal portion of ADPglucose pyrophosphorylase are part of the regulatory domain of the enzyme, critical for allosteric regulation of the enzyme.