title: Hexose phosphate binding sites of fructose-6-phosphate,2-kinase:fructose-2,6-bisphosphatase. Interaction with N-bromoacetylethanolamine phosphate and 3-bromo-1,4-dihydroxy-2-butanone 1,4-bisphosphate.
abstract: N-Bromoacetylethanolamine phosphate and 3-bromo-1,4-dihydroxy-2-butanone 1,4-bisphosphate have been tested in order to study the hexose phosphate binding sites of a bifunctional enzyme, fructose-6-P,2-kinase:fructose-2,6-bisphosphatase. N-Bromoacetylethanolamine phosphate is a competitive inhibitor with respect to fructose-6-P (Ki = 0.24 mM) and a noncompetitive inhibitor with ATP (Ki = 0.8 mM). The reagent inactivates fructose-6-P,2-kinase but not fructose-2,6-bisphosphatase, and the inactivation is prevented by fructose-6-P. The inactivation reaction follows pseudo first-order kinetics to completion and with increasing concentrations of N-bromoacetylethanolamine phosphate a rate saturation effect is observed. The concentration of the reagent giving the half-maximum inactivation is 2.2 mM and the apparent first order rate constant is 0.0046 s-1. The enzyme alkylated by N-bromoacetylethanolamine-P has lost over 90% of the kinase activity, retains nearly full activity of fructose-2,6-bisphosphatase, and its inhibition by fructose-6-P is not altered. 3-Bromo-1,4-dihydroxy-2-butanone 1,4-bisphosphate is also a competitive inhibitor of fructose-6-P,2-kinase with respect to fructose-6-P in the forward reaction and fructose-2,6-P2 in the reverse direction. This reagent inhibits 93% of fructose-6-P,2-kinase but activates fructose-2,6-bisphosphatase 3.7-fold. 3-Bromo-1,4-dihydroxy-2-butanone 1,4-bisphosphate alters the fructose-2,6-P2 saturation kinetic curve from negative cooperativity to normal Michaelis-Menten kinetics with K0.5 of 0.8 microM. The reagent, however, has no effect on the fructose-6-P inhibition of the phosphatase. These results strongly suggest that hexose phosphate binding sites of fructose-6-P,2-kinase and fructose-2,6-bisphosphatase are distinct and located in different regions of this bifunctional enzyme.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D002074:Butanones / Q000378:metabolism*; D004983:Ethanolamines / Q000378:metabolism*; D005636:Fructosephosphates / Q000378:metabolism; D006600:Hexosephosphates / Q000378:metabolism*; D007700:Kinetics; D008433:Mathematics; D025481:Phosphofructokinase-2; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D010770:Phosphotransferases / Q000378:metabolism*
chemical_list: C010690:3-bromo-1,4-dihydroxy-2-butanone 1,4-biphosphate; D002074:Butanones; D004983:Ethanolamines; D005636:Fructosephosphates; D006600:Hexosephosphates; C020161:N-bromoacetylethanolamine phosphate; C027618:fructose-6-phosphate; D000255:Adenosine Triphosphate; D010770:Phosphotransferases; D025481:Phosphofructokinase-2; D010744:Phosphoric Monoester Hydrolases