A recently discovered enzyme is found to have maximum activity in a pH range of 6-8. It is thought that histidine and cysteine residues are a part of the active site. Kinetic experiments of pH dependence in the wild type (WT) enzyme, as well as kinetic experiments at pH 7.0 in site-specific mutants of residues thought to be in the active site, showed the results below. pH KM(mM) Kcat(s^-1)
5 0.14 15
7 0.12 332
9 20.1 281

mutant KM(mM) Kcat(s^-1)
his â phe 0.14 23
cys â ala 33.0 272

Required:
Which Amino acid is primarily involved in Binding?