bio question

[skim1988]

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Phosphofructokinase is a key enzyme that is highly regulated during cellular respiration. Which of the following substances is most likely to stimulate the activity of phosphofructokinase?

The answer is AMP but shouldnt the answer be ATP? Phosphofructokinase phosphorylates an intermediate of glycolysis which requires ATP, so wouldn't ATP be the answer?

 

[Demps]

Phosphofructokinase, or PFK, is bifunctional enzyme that participates in both pathways of glycolysis and gluconeogenesis.

Forget all the hard mechanisms and etc they teach you in biochemistry class.
Just think of the negative feedback inhibition.

PFK going foward glycolytic pathway, it is working to make ATP. In other words, it will be activated when cellular ATP level is low. or AMP for that matter.

In fact, if too much ATP is present, ATP will bind to PFK to inhibit further glycolysis. so ATP is a negative allosteric regulator of PFK.

Hope this helped.

 

[PooyaH]

This has to do with the negative feedback mechanism. Just think about it, would you want to make more ATP, when you already have more than enough? So ATP would inhibit phosphofruktokinase. And when you're in need of more ATP, AMP would act as an enhancer and activates more phosphofruktokinase to get the chain going to make more ATP. Also know that phosphofruktokinase regulates a rate limiting step of glycolysis.

 

[Demps]

This is a powerpoint slide from my biochemistry lecture.

Blue means positive regulator (noted +)
Red means negative regulator (noted -)

 

[skim1988]

thanks guys for clearing things up for me