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?

Cysteine

Explanation:

Determine the Amino acid that is primarily involved in Binding

The Amino acid that is primarily involved in Binding is Cysteine. while the other Amino acid ( i.e.  Histidine ) will be involved in Catalysis.

since the enzyme is functional at pH 6 to 8. and Cysteine has a pH of 5, it should be deprotonated and used primarily for Binding .

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