Explain why serine proteases do not catalyze hydrolysis if the amino acid at the hydrolysis site is a D-amino acid. Trypsin, for example, cleaves on the CC-side of L-ArgArg and L-LysLys, but not on the CC-side of D-ArgArg and D-LysLys.

Explanation:

A protease is an enzyme that catalyzes the hydrolysis of the peptide bonds that tie polypeptide chains together, releasing individual amino acid subunits. The L and D nomenclature for amino acids defines the structure of the glyceraldehyde isomer through which the amino acid can be produced.

SEE BELOW FOR THE APPROPRIATE STRUCTURES.

We need to figure out why swine proteases hydrolyze L-amino acids but not D-amino acids in any way. we know that enzymatic catalysts act as polypeptides if you can recall. They must retain a very precise three-dimensional structure for a catalytic activity to occur. Substrates that do not quite match the required configuration at the active site will not be reacted to — this is a "lock and key" style.

The present exercise may be explained by the fact that the configuration and structure of D-amino acids prevent them from binding properly to the active site of the protease enzyme. Perhaps they're pointed in the wrong direction, or perhaps there happens to be missing electrical interaction that's needed to keep the substrate in position.

Nonetheless, L-amino acids, on the other hand, seem to have the right configurational aspects in the active site and are hydrolyzed.