Inibição enzimática (%)

Percent enzyme inhibition

Percent inhibition measures how far an inhibitor knocks down enzyme activity compared with a control: %inhibition = (v_control − v_sample) / v_control · 100%. Take an Example: a control reads v = 100 and a sample with inhibitor reads v = 30, so %inhibition = (100 − 30)/100 · 100% = 70%. Plot a dose-response curve (%inhibition × log[inhibitor]) and you can pull out the IC50, the inhibitor concentration that cuts activity in half. There are a few flavours of inhibitor. Competitive ones go head to head with the substrate, raising the apparent Km while leaving Vmax untouched; non-competitive ones bind at an allosteric site and pull Vmax down; and mixed inhibitors fall somewhere between the two.

Applications

It sits at the heart of pharmacological screening and drug discovery, where whole inhibitor libraries get tested in high-throughput runs. Industrial enzyme QC relies on it to confirm that batches are free of inhibitors. Environmental toxicology uses it to track acetylcholinesterase inhibition by organophosphates. And in biochemistry teaching it shows up as a go-to kinetics experiment.

FAQ

What is IC50? It is the inhibitor concentration that gets you to 50% inhibition. The lower the IC50, the more potent the inhibitor is against that target.

How are competitive and non-competitive inhibition distinguished? The Lineweaver-Burk plot tells them apart. Competitive inhibition raises the apparent Km but leaves Vmax alone, so the lines meet on the 1/v axis. Non-competitive inhibition lowers Vmax but keeps Km fixed, so the lines meet on the 1/[S] axis.

Can %inhibition be negative? Yes, and when it is, you are looking at activation instead (v_sample > v_control). That signal is handy when you are screening for enzyme activators or allosteric modulators.