hexokinase and PFK question

[morrisol]

i was doing a review on glycolysis and it says that g6p feedback inhibits hexokinase. can someone explain what this means to me?

the other thing that confused me is that in glycolysis PFK is inhibited by ATP. if thats the case then how can it drive the conversion of f6p to f16bp if that step requires atp? like what i mean is, if that step requires atp and pfk is inhibited by atp then wouldnt that inhibit the reaction from proceeding?

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[oncotraum]

Hexokinase is the first enzyme in glycolysis so it is favorable for the cell for that enzyme to be highly regulated. G6P is its product, so it inhibits it by feedback inhibition, which is a very common type of regulation so that we do not constantly make G6P when we already have it in high concentrations. So high concentrations of G6P inhibits hexokinase so we do not make a lot of it when we don't need it.

PFK is the mist highly regulated step in glycolysis because after we make F16BP, we cannot reverse it. Therefore, when we have high concentrations of ATP, we do not need to be using our glucose for glycolysis because there are no energy needs of the cell.

 

[esob]

PFK is allosterically effected by ATP, so while it inhibits it, it does so in gradations based on concentration. The energy coupling that drives the conversion of f6p however is not gradient specific. It is a 1:1 ratio. I don't know if that helps or not but it was how I came to terms with the same question.