Enzymes - Medical Science

Q1:

The role of Asp 102 and His 57 during trypsin catalysis is to

A neutralize the charge on the other's side chain

B keep the specificity pocket open

C function as a proton shuttle

D clamp the substrate into the active site

ANS:C - function as a proton shuttle

Asp 102 and His 57, how do they function as proton shuttles?