2 Katalityczny mechanizm proteazy serynowej(1)

^R' \ ^R

Substrate    ^    /

polypeptide / ^ H

Enzyme-substrate

complex

2

R

+

New C-terminus    /

of cleaved polypeptide o—C

^Ch3in H X

Active enzyme

Figurę 15-23 Catalytic mechanism of the serine proteases. I*hc reaction involves (1) the nucleophilic attack of the active site Ser on the carbonyl carbon atom of the scissilc pcptide bond to form the tctrahedral intcrmediatc;(2) the decomposition of the tetrahedral intermediatc to the acyl-enzyme intermediate through generał acid catalysis by the activc site Asp-polarized His. followed by loss of the aminę product and its replacement by a water molccule; (3) the reversal of Step 2 to form a second tctrahedral intermediate; and (4) the rcvcrsal of Step 1 to yicld the rcaction’s carboxyl product and the active enzyme.