two binding sites for atp are there in pfk.
how many binding sites for atp are there in pfk?
two
in glycolysis, hexokinase is directly inhibited by its product, glucose-6-phosphate, and pyruvate kinase is inhibited by atp itself. the main control point for the glycolytic pathway is phosphofructokinase (pfk), which is allosterically inhibited by high concentrations of atp and activated by high concentrations of amp. 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). the protein has two binding sites for atp – the active site is accessible in either protein conformation, but atp binding to the inhibitor site stabilizes the conformation that binds f6p poorly. a number of other small molecules can compensate for the atp-induced shift in equilibrium conformation and reactivate pfk, including cyclic amp, ammonium ions, inorganic phosphate, and fructose-1,6- and -2,6-biphosphate.
adenosine triphosphate
phosphofructokinase-1 (pfk-1) is one of the most important regulatory enzymes () of glycolysis. it is an allosteric enzyme made of 4 subunits and controlled by many activators and inhibitors. pfk-1 catalyzes the important "committed" step of glycolysis, the conversion of fructose 6-phosphate and atp to fructose 1,6-bisphosphate and adp. glycolysis is the foundation for respiration, both anaerobic and aerobic. because phosphofructokinase (pfk) catalyzes the atp-dependent phosphorylation to convert fructose-6-phosphate into fructose 1,6-bisphosphate and adp, it is one of the key regulatory and rate limiting steps of glycolysis. pfk is able to regulate glycolysis through allosteric inhibition, and in this way, the cell can increase or decrease the rate of glycolysis in response to the cell's energy requirements. for example, a high ratio of atp to adp will inhibit pfk and glycolysis. 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.
phosphofructokinase 1