Researchers isolated a yeast phosphofructokinase mutant in which a serine at the fructose-2,6-bisphosphate (F26BP) binding site was replaced with an aspartate residue. The amino acid substitution completely abolished the binding of F26BP to PFK. There was a dramatic decline in glucose consumption and ethanol production in the mutant compared to control yeast. Required:
a. Propose a hypothesis that explains why the mutant PFK cannot bind F26BP.
b. What does the decline of glucose consumption and ethanol production in the yeast reveal about the role of F26BP in glycolysis?

Explanation:

a.

Phosphofructokinase-1, also known as the glycolysis stimulator, is among the most important glycolysis regulatory enzymes. It's an apoptotic enzyme with effectors (activators/inhibitors) that control its activity. Fructose 6-phosphate and ATP are converted to fructose 1,6-bisphosphate and ADP by PFK-1.

Suppose the serine in PFK's active site is substituted with aspartic acid, the enzyme's active site would be devoid of phosphorylation sites. The enzyme PFK contributes to the transferase family since it has kinase activity. It serves as an acceptor by transferring phosphorus groups to an alcohol group (serine).

Insulin stimulates protein phosphatase, which eliminates the phosphate group from the serine residue, stabilizing the kinase role and promoting F26BP formation. The phosphorylation reaction will not take place provided the serine is substituted with aspartic acid. Therefore, the PFK's kinase activity will be lost. Similarly, F26BP will not form PFK, and it will not be aborted in the future.

b.

Their decline reveals that:

F26BP increases the overall net flow of glucose by glycolysis modulates PFK production and induces Fructose 1,6 bis phosphatase, which also catalyzes the glycolysis reverse process.

Fructose-2,6-bisphosphate transcriptionally activates the rate-limiting process of glycolysis catalyzed by PFK 1.

Increased levels of Fru-2,6-P2 located in the liver raise PFK1's propensity and resistance for fructose 6 phosphate while lowering its affinity for its' inhibitors ATP and citrate.

Fructose 2,6-bisphosphate supersedes the inhibition of ATP and promotes greater sensitivity of the eukaryotes to be regulated by hormones (glucagon and insulin).

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