Inhibitors
Pepsin may be inhibited by high pH (see "Activity" and "Stability", above) or by inhibitor compounds. Pepstatin is a low molecular weight compound and potent inhibitor specific for acid proteases with a Ki of about 10−10 M for pepsin. The statyl residue of pepstatin is thought to be responsible for pepstatin inhibition of pepsin; statine is a potential analog of the transition state for catalysis by pepsin and other acid proteases. Pepstatin does not covalently bind pepsin and inhibition of pepsin by pepstatin is therefore reversible. 1-bis(diazoacetyl)-2-penylethane reversibly inactivates pepsin at pH 5, a reaction which is accelerated by the presence of Cu(II).
Pepsin also undergoes feedback inhibition; a product of protein digestion slows down the reaction by inhibiting pepsin.
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