Acid-base catalytic mechanism and pH dependence of fructose 2,6-bisphosphate activation of the Ascaris suum phosphofructokinase.
A form of phosphofructokinase (PFK) from Ascaris suum desensitized to hysteresis in the reaction time course and ATP allosteric inhibition has been used to study the activation by fructose 2,6-bisphosphate (F26P2) at varied pH in both reaction directions. In the direction of phosphorylation of F6P, V and V/KMgATP are constant over the pH range 6-9, while V/KF6P decreases at low pH, giving a pK value of 7.0, and at high pH, giving a pK of 8.9. V and V/KMgATP are insensitive to the presence of F26P2, but V/KF6P is increased by a constant amount in the presence of saturating F26P2 over the entire pH range studied. The concentration of F26P2 that gives half the change in V/KF6P, Kact, increases as the pH decreases, giving a pK of 7.4, reflecting an enzyme group that must be unprotonated for optimum binding of F26P2. In the direction of phosphorylation of MgADP, V and V/KMgADP are pH-independent, and both are insensitive to the presence of F26P2. V/KFBP decreases at high pH, giving a pK of about 7.3, and is increased by a constant amount in the presence of F26P2 over the entire pH range studied.(ABSTRACT TRUNCATED AT 250 WORDS)
Payne
M A
MA
Department of Biochemistry and Molecular Biology, University of North Texas Health Science Center at Fort Worth 76107-2699, USA.
Rao
G S
GS
Harris
B G
BG
Cook
P F
PF
D000244:Adenosine Diphosphate / Q000378:metabolism; D000494:Allosteric Regulation; D000818:Animals; D017165:Ascaris suum / Q000201:enzymology*; D002384:Catalysis; D005635:Fructosediphosphates / Q000378:metabolism*; D005636:Fructosephosphates / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008956:Models, Chemical; D010732:Phosphofructokinase-1 / Q000378:metabolism*; D010766:Phosphorylation
D005635:Fructosediphosphates; D005636:Fructosephosphates; D000244:Adenosine Diphosphate; C027618:fructose-6-phosphate; C027652:fructose 2,6-diphosphate; D010732:Phosphofructokinase-1