Effector Actions may be Inhibitory (top) or Activating (bottom)

I’ve been looking for an animation (or something similar) that would illustrate how enzyme activity can be regulated by effectors. However, this seems to be lacking… I’m thinking about making one myself and will post it here if I do.

Recall that effectors are the molecules that bind to enzymes outside of the active site and have either a positive (activator) or negative (inhibitor) effect on the enzyme’s activity. Regardless of the positive or negative effect, both of these molecules are considered effectors and bind to an effector site. The effector site can be any location on the enzyme other than the active site. Inhibitory effectors are called non-competitive inhibitors because they do not compete with the binding of substrate directly at the active site. Activating effectors are called activators. Because these molecules bind away from the active site, they do not directly interact with the substrate, but instead influence the enzyme’s ability to bind (and/or modify) substrate by changing the shape of the enzyme. For this reason, enzymes that bind effectors are called allosteric enzymes, from the greek allo– ‘other’ and steric ‘shape/ conformation.’

Allosteric enzymes can be in one of two conformations: Active Conformation or Inactive Conformation. The conformation state that these enzymes exist in is dependent upon the presence or absence of their effector proteins.

Competitive Inhibition

The other major class of regulator is that of competitive inhibitors, these molecules bind directly to an enzyme’s active site and prevent substrate processing. This is a much more straightforward kind of inhibition and does not alter a enzyme’s shape into an inactive conformation.

I hope this helps to organize your thoughts about enzyme regulation. I plan on reviewing this in class this week using a couple example problems.