I think you have reduced the activity by interlocking the enzyme. Why would you want to add a cycteine and introduce a disulphide bond bridge, normally, researchers would remove the cysteine and replace with other amino acid.

 Dear Ag Muhammad Sagaf Abu Bakar

thanks, I introduced disulfide bond in order to increase protein stability

Dear Zahra,

Are you producing this enzyme in recombinant form? What host did you use?

yes

What expression host are you using? Prokaryotic or eukatyote expression system?

Procaryotic