THE N-TERMINAL REGION IS IMPORTANT FOR THE ALLOSTERIC ACTIVATION AND INHIBITION OF THE ESCHERICHIA-COLI ADP-GLUCOSE PYROPHOSPHORYLASE

The ADPglucose pyrophosphorylase (EC 2.7.7.27) from Escherichia coli i s allosterically activated by fructose 1,6-bisphosphate and inhibited by AMP. Proteolysis of the enzyme with proteinase K causes loss of act ivity and generates two peptides, 21 and 28 kDa, from the 49.7-kDa sub unit. 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 Met(181)-Ala(182) and Phe(192)-Val(193 ). Proteolysis of the protected enzyme removed 10 to 13 amino acids fr om the N-terminal and 2 amino acids from the C-terminal. The resulting enzyme was almost independent of the need for fructose 1,1,6-bisphosp hate for maximal activity and insensitive to inhibition by AMP. The ap parent affinity for the substrates was similar to that of the fully-ac tivated wild-type enzyme. These data suggest that amino acid residues in the N-terminal portion and possibly the C-terminal portion of ADPgl ucose pyrophosphorylase are part of the regulatory domain of the enzym e, critical for allosteric regulation of the enzyme. (C) 1998 Academic Press.