My Biochemistry book mentions that 'competitive inhibition' is a reversible form of inhibition.
But given that the inhibitor is blocking the active site and prevents an enzyme-substrate complex to be formed, how can it be reversible?
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$\begingroup$ Not all competitive inhibition is permanently irreversible. Only substrates which bind covalently are irreversible. Something like Narcan(Naloxone) is a competitive antagonist, but it is not permanent. $\endgroup$– DonJulianMar 2, 2016 at 9:06
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A competitive inhibitor typically competes for the active site with the substrate. In this textbook case, binding of a competitive inhibitor is reversible, because it binds to the active site of the enzyme, but is also released, making way for the substrate to bind. The affinity of the substrate, as well as its concentration determine the amount of inhibition (Berg et al., 2002).
An irreversible inhibitor may covalently bind to the active site, permanently disabling the enzyme (McDonald et al., 2012).
References
- McDonald et al., Enzymes: Irreversible Inhibition. In: eLS. John Wiley & Sons Ltd, Chichester (2012)
- Berg et al., Biochemistry. 5th ed. New York: W H Freeman; (2002)
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3$\begingroup$ In light of this meta post, this might be the single greatest answer of all time. I had a good laugh. $\endgroup$ Jul 21, 2017 at 19:00
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1$\begingroup$ @canadianer thanks :-) It was a bit of an over-reactive response to someone claiming the answer was undersourced (a whole string of comments has been deleted since). Admittedly, it was indeed undersourced, but to me its contents are common knowledge and I didn't even bother to source it. Well, after it had been scrutinized even in a meta post, others began to interfere, mainly long-term residents here who knew I was probably among the last deserving to be blamed for not sourcing his answer :) Eventually it lead to the above result.... $\endgroup$– AliceD ♦Jul 25, 2017 at 12:33
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2$\begingroup$ The high number of upvotes is totally not representative of its quality, it's just that people appreciate the principle of sourcing answers to that extreme point where it becomes just plain silly :) $\endgroup$– AliceD ♦Jul 25, 2017 at 12:33
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$\begingroup$ @xusr thanks for your input. It sounds like you could write an excellent answer. In the meantime, I have adapted the wording of my answer above to reflect your thoughts. My approach was to give a schoolbook answer to a schoolbook question. Nothing more, nothing less. $\endgroup$– AliceD ♦Mar 24, 2018 at 19:19
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1$\begingroup$ It's water under the bridge, but if I were writing a schoolbook answer I would have included a diagram and an equation. School books are the most highly reviewed and edited form of literature. The publishers stand to lose a lot if they get things wrong in a very lucrative corner of the market. $\endgroup$– DavidMar 25, 2018 at 19:22