 Solution

An ionizable Asp296 carboxyl group is not essential to the measured catalytic pathway at pH 7. Asparagine retains a similar side-chain size and an amide donor/acceptor pair, while losing the carboxyl group's ordinary acid/base chemistry and negative charge. Preserved kinetics are therefore consistent with a binding or positioning hydrogen bond that survives the conservative substitution, or with a dispensable/redundant contact.

This does not prove that Asp296 makes no interaction in the native enzyme, nor that every substitution at that position would be harmless. The displayed Asp296 contact is also distinct from Asp295, which coordinates zinc; their neighboring residue numbers must not be conflated. Other pH values could expose a contribution hidden by the assay condition.