... distance of 3.5 A˚, and the shortestdistance between the imidazole ring of His 210 and the atoms of Asp 113 is 3.2 A˚. The substrate binding subsite in API is composed of His 210 -Gly 211 -Gly 212 , ... (W169Y), Phe(W169F), His (W169H), Leu (W169L), Val (W169V), and Ala (W169A), His 210 mutants replaced by Ala (H 210 A),Ser (H 210 S), and Lys (H 210 K), and double mutantsW169F–H 210 A and W169A–H 210 A ... subsite residues of trypsin and API are Ser 214 –Trp 215 –Gly 216 and His 210 –Gly 211 –Gly 212 , respectively. S1pocket is the substrate binding site for the side-chain of Lys (API) or Lys and Arg (trypsin).The...