title: Presteady-state kinetic evidence for a ring-opening activity in fructose-1,6-(bis)phosphate aldolase.
abstract: Fructose 1,6-bisphosphate aldolase, a glycolytic enzyme, catalyzes the cleavage of fructose 1,6-bisphosphate, resulting in two three-carbon products. The reaction of the class I enzymes, which utilize a Schiff-base intermediate, requires that the hexose be in the open-chain form. This form comprises only 1-2% of the sugar at equilibrium. The chemical form of the substrate that binds to aldolase and begins the catalytic cycle has not been unequivocally demonstrated. Transient-state kinetics in single-turnover experiments of fructose 1,6-bisphosphate with aldolase in excess reveals the rates of the intermediate steps in the cleavage reaction, including those from initial binding to Schiff-base formation. The rate of hexose Schiff-base formation was faster than the uncatalyzed rate for ring-opening of either the alpha- or beta-furanose at 4 degrees C. In addition, approach-to-equilibrium experiments reveal that aldolase binds and reacts first with 70% of fructose-1,6-bisphosphate in a fast reaction, consistent with the amount of beta-anomer in solution, and with the remaining 30%, presumably the alpha-anomer, in a slow reaction. These results indicate that aldolase must catalyze the ring-opening step and that there may be a previously unrecognized second active site on the enzyme for catalyzing this reaction.
authors.affiliation: Biology Department, Boston University, Boston, Massachusetts 02215, USA.
authors.forename: Kyung H
authors.initials: KH
authors.lastname: Choi
authors.forename: Dean R
authors.initials: DR
authors.lastname: Tolan
mesh_terms: D005634:Fructose-Bisphosphate Aldolase / Q000737:chemistry* / Q000378:metabolism*; D005635:Fructosediphosphates / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D012545:Schiff Bases / Q000737:chemistry / Q000378:metabolism
chemical_list: D005635:Fructosediphosphates; D012545:Schiff Bases; D005634:Fructose-Bisphosphate Aldolase; C029063:fructose-1,6-diphosphate