What are the main components of Bifunctional enzymes? What does the Bif enzyme d
ID: 150830 • Letter: W
Question
What are the main components of Bifunctional enzymes? What does the Bif enzyme do to regulate glycolysis and gluconeogenesis? Which enzymes in gluconeogenic pathways are regulated by the Bif enzyme? How is the Bif enzyme regulated in the fed and fasted state, respectively? What are the main components of Bifunctional enzymes? What does the Bif enzyme do to regulate glycolysis and gluconeogenesis? Which enzymes in gluconeogenic pathways are regulated by the Bif enzyme? How is the Bif enzyme regulated in the fed and fasted state, respectively?Explanation / Answer
Bifunctional enzymes stay in a state with two isoforms. In case of phosphofructokinase, the monomers of the bifunctional protein are divided into two functional domains. Kinase domain is located on the N-terminal, which consists of a central six-stranded sheet and five parallel strands, an antiparallel edge strand which is surrounded by seven helices. This domain contains nucleotide-binding fold at it’s C-terminal end of the -strand. The PFK-2 domain is closely related to the mononucleotide binding proteins. The phosphatase domain is located on the C-terminal. The domain has a six-stranded central sheet and an additional -helical subdomain which covers the active site of the molecule. The N-terminal region modulates PFK-2 and FBPase2 activities, to stabilize the dimer form of the enzyme.
Phosphofructokinase catalyzes the formation and degradation of an allosteric regulator, fructose 2-6, bisphosphate from fructose-6-phosphate. Fructose 2,6 bisphosphate contributes the rate determining step in glycolysis, because it activates Phosphofructokinase in the glycolysis pathway, and inhibits fructose-1,6-bisphosphatase in gluconeogenesis.
Fructose 1,6-bisphosphatase is an enzyme, controls gluconeogenic pathway, which gets regulated by a bif enzyme. This enzyme is regulated by fructose-2,6- bisphosphate, which is formed rom fructose-6-phosphate by the action of a bifunctional enzyme that, depending on its own state of phosphorylation, either catalyzes phosphorylation of fructose-6-phosphate to fructose-2,6-bisphosphate or dephosphorylation of fructose-2,6-bisphosphate to fructose-6-phosphate. This enzyme is a substrate of protein kinase A, and acts as a phosphatase when it is phosphorylated.
Phosphofructokinase transfers the phosphate residue of ATP to the hydroxyl residue of Fructose-6-phosphate, results in fructose 1,6-bisphosphate. After ingestion of a meal that is in a fed state, fructose-2,6-bisphosphate is elevated and results in a speedy glycolysis reaction. Before a meal, that is in a fasted state, the concentration of fructose-2,6- bisphosphate is decreased, and results in upregulation of F1,6BP which facilitates the gluconeogenesis.
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