Answer to Question #318902 in Organic Chemistry for Anku

Question

which amino acid can act in both general acid and general base catalysis at neutral pH?

Answer 1

The amino acid serving as a general acid should have a pKa greater than physiological pH, so that it is protonated in the enzyme active site. Common amino acid residues capable of performing that function include His, Cys, Tyr, Lys and Arg (all have pKa's near or above 7).