The interaction of monovalent cations with fructose 1,6-bisphosphatase modified by N-ethylmaleimide and its relation with AMP inhibition
Reyes, A.; Rodríguez, P.; Slebe, J.C.
Biochemistry International 26(2): 347-356
1992
ISSN/ISBN: 0158-5231 PMID: 1558547 Document Number: 394246
The relationship between derivatization of reactive cysteine residues with N-ethylmaleimide and a partial desensitization of fructose 1,6-bisphosphatase to AMP inhibition was studied. AMP desensitization of the enzyme was found to be dependent on the activity assay conditions used. When the assay was performed in the presence of high levels of monovalent cations (150 mM), the AMP affinity of the enzyme decreased with the chemical modification. The apparent loss of sensitivity toward AMP was accompanied by an uptake of 1 mole of N-ethylmaleimide/mole of enzyme subunit. However, the modified enzyme did not show alteration in AMP inhibition in the absence of K+. Evidence was obtained that K+ induces a conformational change on the enzyme derivative, which hinders AMP interaction with the protein. The results point to the importance of selecting suitable conditions for the study of the regulatory properties in allosteric enzymes.