Serine protease with peptide

Coombs, G. S., Rao, M. S Olson, A. J., Dawson, P. E and Madison, E. L. (1999) Revisiting catalysis by chymotrypsin family serine proteases using peptide substrates and inhibitors with unnatural main chains. J. Biol. Chem. 274, 24074-24079. 

Figure 3. Reaction of a serine protease with a peptide chloromethyl ketone. The side chain of the Pt residue of the inhibitor is shown interacting with the primary substrate binding subsite (SJ of the enzyme.

The mechanism of peptide bond synthesis is thought to resemble the reverse of the acylation step in the serine protease, with the base of A2486 (A2451 in E. coli) playing the same general base role as histidine-57 in chymotrypsin. This A is universally conserved within the central loop of domain V [28]. 

Reaction of Serine Proteases with Aza-Amino Acid and Aza-Peptide Derivatives... 

Percutaneous absorption is another route of interest for the administration of peptides [158], with metabolism being a complicating factor [159]. Thus, [Leu5]enkephalin and Tyr-Pro-Leu-Gly-NH2 were rapidly degraded on the dermal side after penetration through rat skin preparations [160]. The use of inhibitors confirmed the involvement of serine proteases and metalloenzymes. 

As discussed above, proteases are peptide bond hydrolases and act as catalysts in this reaction. Consequently, as catalysts they also have the potential to catalyze the reverse reaction, the formation of a peptide bond. Peptide synthesis with proteases can occur via one of two routes either in an equilibrium controlled or a kinetically controlled manner 60). In the kinetically controlled process, the enzyme acts as a transferase. The protease catalyzes the transfer of an acyl group to a nucleophile. This requires an activated substrate preferably in the form of an ester and a protected P carboxyl group. This process occurs through an acyl covalent intermediate. Hence, for kineticmly controlled reactions the eii me must go through an acyl intermediate in its mechanism and thus only serine and cysteine proteases are of use. In equilibrium controlled synthesis, the enzyme serves omy to expedite the rate at which the equilibrium is reached, however, the position of the equilibrium is unaffected by the protease. 

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