Why does this chelating agent, that doesnt bind the necessary cofactor, slow dow

Question

Why does this chelating agent, that doesnt bind the necessary cofactor, slow down the reaction slightly compared to the control (with no chelating agent)?

We measured the absorbance of chelating agents reacted with catecholase, to form benzoquinone (a brown substance). Since the control didnt have a chelating agent, the cofactor (copper) needed was there and it catalyzed effectively. EDTA doesnt bind to copper but it still had a slightly lower catalyzation of the reaction. Why is this?

Edit: EDTA binds to magnesium and calcium. To catalyze a reaction forming brown substance benzoquinone, magnesium and copper are not necessary cofactors for the enzyme, as shown by EDTA having a large change in absorbance. In solutions where chelating agents bind to copper, there is a much smaller change in absorbance, since little brown benzoquinone is formed. This indicates copper is a necessary cofactor for benzoquinone to be formed. So why, if magnesium and calcium arent necessary cofactors, is their absorbance slightly lower than the control (where all cofactors are present)? is it because magnesium and calcium are necessary to a small degree?

Explanation / Answer

Yes, the chelating agent EDTA will interfare in the reaction and the production of product. As EDTA is a reactive molecule it shows interaction with metals like from d orbital . As it is mentioned in case of calcium and magnesium EDTA makes complex with them and leads to increase in absorbance value where as such case not found in copper. It means EDTA makes stronger complex with calcium and magnesium so to restrict EDTA to not interfairs in the reaction the addition of magnesium and calcium is needed.

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