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The key difference between the regulation of PFK in eukaryotes and prokaryotes is that in eukaryotes PFK is activated by fructose 2,6-bisphosphate. The purpose of fructose 2,6-bisphosphate is to supersede ATP inhibition, thus allowing eukaryotes to have greater sensitivity to regulation by hormones like glucagon and insulin. [2]
PFK is about 300 amino acids in length, and structural studies of the bacterial enzyme have shown it comprises two similar (alpha/beta) lobes: one involved in ATP binding and the other housing both the substrate-binding site and the allosteric site (a regulatory binding site distinct from the active site, but that affects enzyme activity).
d -Glucose + 2 [NAD] + + 2 [ADP] + 2 [P] i 2 × Pyruvate 2 × + 2 [NADH] + 2 H + + 2 [ATP] + 2 H 2 O Glycolysis pathway overview The use of symbols in this equation makes it appear unbalanced with respect to oxygen atoms, hydrogen atoms, and charges. Atom balance is maintained by the two phosphate (P i) groups: Each exists in the form of a hydrogen phosphate anion, dissociating to contribute ...
Phosphofructokinase, or PFK, catalyzes the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate and is an important point in the regulation of glycolysis. High levels of ATP, H +, and citrate inhibit PFK. If citrate levels are high, it means that glycolysis is functioning at an optimal rate. High levels of AMP stimulate PFK.
The inhibition of PFK by ATP is unusual since ATP is also a substrate in the reaction catalyzed by PFK; the active form of the enzyme is a tetramer that exists in two conformations, only one of which binds the second substrate fructose-6-phosphate (F6P).
Fru-2,6-P 2 strongly activates glucose breakdown in glycolysis through allosteric modulation (activation) of phosphofructokinase 1 (PFK-1).Elevated expression of Fru-2,6-P 2 levels in the liver allosterically activates phosphofructokinase 1 by increasing the enzyme’s affinity for fructose 6-phosphate, while decreasing its affinity for inhibitory ATP and citrate.
In enzymology, 1-phosphofructokinase (EC 2.7.1.56) is an enzyme that catalyzes the chemical reaction. ATP + D-fructose 1-phosphate → ADP + D-fructose 1,6-bisphosphate. Thus, the two substrates of this enzyme are ATP and D-fructose 1-phosphate, whereas its two products are ADP and D-fructose 1,6-bisphosphate.
The underlying force driving these reactions is the Gibbs free energy of the reactants relative to the products. If donor and acceptor (the reactants) are of higher free energy than the reaction products, the electron transfer may occur spontaneously. The Gibbs free energy is the energy available ("free") to do work.