An enzyme has Km = 1.5 mmol/L. A competitive inhibitor is present at four times its Ki…
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An enzyme has mmol/L. A competitive inhibitor is present at four times its .
- What is the apparent with the inhibitor?
- At a substrate concentration of 3.0 mmol/L, what share of does the enzyme reach with the inhibitor?
- What substrate concentration would give the share that the enzyme reaches at 3.0 mmol/L without the inhibitor?
- Would adding substrate help if the inhibitor were non-competitive?
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 apparent . mmol/L.
Step 2. The share with the inhibitor. , which is 28.6 %.
Step 3. The substrate needed. Without the inhibitor the share at 3.0 mmol/L is . With the inhibitor, a share of two thirds needs mmol/L, which is five times as much.
Step 4. The non-competitive case. No. A non-competitive inhibitor lowers , and no amount of substrate brings it back.
Answer: 7.5 mmol/L; 28.6 %; 15 mmol/L; no.
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