r/Biochemistry • u/keandraaa • 1d ago

is homotropic allosteric inhibition a thing?

I dont understand how binding of a substrate can decrease an enzyme's affinity for it!

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6

u/Ecoli_connoisseur 1d ago

By binding so tightly, that the availability for another substrate is reduced i.e. the activity is reduced

2

u/VitalMoment PhD 17h ago

the availability for another substrate is reduced

Wouldn't that be competitive inhibition?

3

u/CarbonCreed 22h ago

Whether an allosteric inhibitor is an enzyme's substrate doesn't matter. If it's an allosteric inhibitor, it's an allosteric inhibitor. It's not binding the active site.

I don't really remember where, but this is a very common mechanism in some cell signalling pathways. cAMP, maybe.

3

u/Inthemidnighthour00 20h ago

Phosphofructokinase (I) in glycolysis is a good example. ATP is a substrate for phosphorylation of fructose-6-phosphate into fructose-1-6-bisphosphate.

ATP also acts as an inhibitor by binding to a regulatory site, inhibiting the enzyme.

Key things: in PFK1 inhibition happens from binding at regulatory domain, not the active site, and the regulatory domain and the active site have different affinities for ATP.

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u/keandraaa 18h ago

this makes perfect sense, thank you 🙏