Essential arginyl residues in fructose-1,6-bisphosphatase

Abstract

Modification of pig kidney fructose-1,6-bisphosphatase [EC 3.1.3.11] with 2,3-butanedione in borate buffer (pH 7.8) leads to the loss of the activation of the enzyme by monovalent cations, as well as to the loss of allosteric AMP inhibition. In agreement with the results obtained for the butanedione modification of arginyl residues in other enzymes, the effects of modification can be reversed upon removal of excess butanedione and borate. Significant protection to the loss of K+ activation was afforded by the presence of the substrate fructose 1,6-bisphosphate, whereas AMP preferentially protected against the loss of AMP inhibition. The combination of both fructose 1,6-bisphosphate and AMP fully protected against the changes in enzyme properties on butanedione treatment. Under the latter conditions, 1 arginyl residue/mol of enzyme subunit was modified, whereas 3 arginyl residues were modified by butanedione under conditions leading to the loss of both K+ activation and AMP inhibition. The modification of 2 arginyl residues per subunit would appear to be responsible for the change in enzyme properties. One arginyl residue/subunit is probably essential for monovalent cation activation, and another arginyl residue is essential for AMP inhibition. A likely role of the latter residue could be its involvement in the binding of the phosphate group of AMP.