The enzyme phosphofructokinase (PFK) catalyzes a key step in glycolysis and is inhibited by high levels of which of the following molecules?

Question

BlackTom AI · Accepted Answer

The prompt asks to evaluate each answer option in the context of the regulation of phosphofructokinase (PFK) in glycolysis.
Option 1: 'glucose and NAD+' These molecules are substrates or coenzymes in other steps of metabolism, not classic inhibitors of PFK. Glucose is the substrate for glycolysis, and NAD+ is a cofactor in later redox steps; neither functions as an allosteric inhibitor for PFK. Therefore this statement is incorrect.
Option 2: 'AMP and ATP' This pair contains ATP, which is a well-known inhibitor of PFK due to feedback from high-energy status. However, AMP typically acts as an activator of PFK, signaling low energy and promoting glycolysis. The combination 'AMP and ATP' misrepresents the regulatory effects because the activating influence of AMP would counter the inhibitory effect of ATP, making the overall assertion misleading. Thus this option is incorrect.
Option 3: 'ATP and citrate' This option lists two well-established allosteric inhibitors of PFK. ATP signals high-energy status and suppresses glycolysis by inhibiting PFK. Citrate, an intermediate of the citric acid cycle, also inhibits PFK by signaling that energy production intermediates are sufficient, thereby downregulating glycolytic flux. This combination accurately reflects known regulation and is correct.
Option 4: 'citrate and CO2' Citrate is an inhibitor of PFK, but CO2 is not a recognized allosteric regulator of PFK in glycolysis. Since CO2 does not serve as a key inhibitory effector for PFK in standard metabolic control, this option is incorrect.
In summary, the statements in options 1, 2, and 4 contain either incorrect targets or incomplete/regulatory misunderstandings about PFK inhibition, while option 3 correctly identifies ATP and citrate as inhibitory effectors of PFK.

The enzyme phosphofructokinase (PFK) catalyzes a key step in glycolysis and is inhibited by high levels of which of the following molecules? 单项选择题

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