In a resting muscle the level of ATP is high…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
In a resting muscle the level of ATP is high. In a sprint ATP is used up quickly and the level of AMP rises. The enzyme phosphofructokinase-1 (PFK-1) carries out the first committed step of glycolysis.
- What do ATP and AMP do to PFK-1, and why does this suit the cell?
- Why does the cell control glycolysis at the PFK-1 step and not at the last step?
- What kind of regulation is this, and what does the curve of rate against fructose 6-phosphate look like?
Need a reminder? The key ideaShow
Competitive inhibitor: , unchanged, with . Non-competitive inhibitor: , unchanged. Feedback from an end product usually acts on the first committed step, and a regulated enzyme such as phosphofructokinase-1 has activators and inhibitors that bind away from its active site.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The effectors. ATP binds an allosteric site on PFK-1 and slows it. AMP and ADP bind there and speed it up. At rest ATP is plentiful, so glycolysis idles. In a sprint ATP falls and AMP rises, so PFK-1 speeds up and the muscle makes the ATP that it needs.
Step 2. The place of control. PFK-1 carries out the first step that is committed to glycolysis. Stopping there keeps the cell from making and piling up all the later intermediates. Control at the last step would let them build up.
Step 3. The kind. It is allosteric regulation, with feedback from the product ATP. PFK-1 has several subunits that help each other, so the curve of rate against fructose 6-phosphate is S-shaped, not a hyperbola.
Answer: ATP slows PFK-1 and AMP speeds it, so glycolysis follows the demand for ATP. It is controlled at the first committed step, by allosteric regulation with a sigmoid curve.
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