Question

I learned competitive inhibition and non-competitive inhibition.

My teacher told me that we should say that non-competitive inhibitors bind to somewhere on the enzyme apart from active sites.

I thought 'somewhere on the enzyme apart from active sites' refers to allosteric site. Because allosteric means changing shape and non-competitive inhibitors do change the tertiary structure of enzymes. However my teacher said this is wrong -- non-competitive inhibitors do bind to allosteric sites but they also bind to some other sites as long as they don't bind to active sites.

So, I am wondering, apart from allosteric sites, where else can non-competitive bind to? Or, is my teacher wrong?

Answer 1

Non-competitive inhibitors can bind to allosteric sites or other non-active sites on the enzyme that affect its activity. They can cause conformational changes that impact the active site indirectly, representing a mechanism of allosteric control. Therefore, binding to any site apart from the active site that influences enzyme activity is considered non-competitive inhibition.

Step-by-step explanation:

Your teacher's explanation aligns with current understanding in enzymology. A non-competitive inhibitor may indeed bind to an allosteric site; however, it's possible for such inhibitors to bind to other locations on an enzyme as well. The key defining factor is that these inhibitors do not bind at the enzyme's active site. The allosteric site is just one example of where non-competitive inhibitors can attach. These sites induce conformational changes in the enzyme, which in turn affect the active site's ability to bind to its substrate or affect its catalytic activity. Beyond allosteric sites, non-competitive inhibitors might bind to regulatory domains or interfaces between enzyme subunits in multimeric enzymes. In doing so, they can affect the enzyme's function without directly competing with the substrate at the active site.

Allosteric inhibition is a specific case where the binding of the inhibitor to an allosteric site affects the active site, but this concept can be expanded more generally to settings where non-competitive inhibitors bind to other non-active sites that are crucial for the enzyme's catalytic activity.

Therefore, it is correct to say that non-competitive inhibitors can bind to allosteric sites or any other site apart from the active site that, when bound, affects enzyme activity. This can result in a decrease in the enzyme's ability to facilitate the conversion of substrate into product. Engaging in these other sites is a part of the broad mechanism of allosteric control, which regulates enzyme activity.