Small-molecule inhibitor: NPGB

Name

History: NPGB was described as an inhibitor and active-site titrant of trypsin by Chase & Shaw (1967).
Peptidases inhibited: Inhibits trypsin, plasmin and thrombin (Chase & Shaw, 1969). Various S1-family peptidases from snake venoms also are inhibited (e.g. batroxobin: Sturzebecher et al., 1986). Despite its different specificity, dipeptidyl-peptidase II is also inhibited by NPGB (McDonald & Schwabe, 1980). NPGB is rapidly hydrolysed by, and therefore does not inhibit, an unsequenced serine peptidase or mixture of serine peptidases that is present in mammalian tissues termed 'guanidinobenzoatase' (##S9G.013## or ##S9G.081##: Poustis-Delpont et al., 1994; Steven, 2004).
Mechanism: NPGB is a slowly-hydrolysed substrate of trypsin and many serine peptidases with similar specificity. The rate of acylation of the enzyme is much faster than its deacylation, so that the compound acts as a temporary inhibitor (Chase & Shaw, 1969). The "burst" of release of p-nitrophenol in the acylation reaction is easily monitored spectrophotometrically, and allows determination of the active site molarity of the peptidase.

Inhibitor class: This compound is of the class of acylating agents of serine peptidases. Such compounds acylate the active site serine to form an acyl enzyme that is much more stable than that formed in normal catalysis, as a result of geometric or electrostatic effects. This class of inhibitors has been reviewed by Powers & Harper (1986) (pp. 108-119) and Powers et al. (2002) (pp. 4695-4728).
Reviews: Chase & Shaw (1969); Powers & Harper (1986) (pp. 108-109)