Things That Bind To Enzymes Besides Substrates

Things that Bind to Enzymes (besides substrates) A look at cofactors, coenzymes, prosthetic groups and inhibitors

Prosthetic Groups ♦ Many enzymes need help from other

molecules to function properly ♦ These other, non-protein, inorganic molecules are called COFACTORS ♦ They bind to the enzyme and help it work ♦ Example: carbonic anhydrase needs a Zn2+ ion bound to it to work properly

Carbonic anhydrase

Coenzymes are organic compounds ♦ Organic prosthetic groups are called

COENZYMES ♦ Which one was the zinc ion in carbonic anhydrase?

Inhibitors ♦An INHIBITOR is any chemical

that slows a reaction down. ♦There are 4 types of inhibitors, depending on how they work and how they affect the enzyme

Category 1: competitive inhibitors ♦These inhibitors compete with the

substrate for the active site ♦When a competitive inhibitor binds to the active site, it prevents the real substrate from binding there

Reversible vs non-reversible ♦ REVERSIBLE competitive inhibitors

only block the active site when attached to the enzyme, but don’t stay attached to the active site ♦ NONREVERSIBLE competitive inhibitors become permanently attached to the active site

Competitive Inhibitors

Category 2: Noncompetitive inhibitors ♦ These inhibitors bind to the enzyme

somewhere else besides the active site ♦ They “warp” the shape of the enzyme, and prevent it from working properly ♦ REVERSIBLE NONCOMPETITIVE INHIBITORS only change the shape of the enzyme when they are attached to the enzyme;when they detach the enzyme regains its usual shape and can work again

Noncompetitive Inhibition

Noncompetitive, nonreversible inhibitors ♦These inhibitors permanently

damage the enzyme ♦Even after they are removed the enzyme cannot work anymore ♦Like a bent paper clip

Inhibitor Types: Summary

Competitive

Reversible

Non-reversible

Reversible, Competitive

Non-reversible, Competitive

Non-competitive Reversible, Non-reversible, Non-competitive Non-competitive