Question

In class, we discussed the catalytic mechanism for the conversion of 2-phosphoglycerate to phosphoenolpyruvate by the enzyme enolase. The enzyme can also catalyze the reverse reaction and convert phosphoenolpyruvate to 2-phosphoglycerate. a.) Sketch the electron pushing mechanism for the reverse reaction. Be sure to include the catalytic lysine and glutamate in your mechanism.

b.) Is glutamate a general acid or base in the reverse reaction? How about lysine?

c.) Ethylenediaminetetraacetic acid (EDTA) is a chelating agent that sequesters divalent metal ions. Addition of EDTA to enolase results in loss of catalytic activity. Explain.

Answer 1

a. The conversion of 2 PGA to PEP is a dehydration reaction which involves the removal of the water molecule . This reaction is a reversible reaction and hence the reverse of this is the conversion of PEP to PGA hence an addition of water molecule is required for this reaction and water acts as a nucleophile and attacks the carbonyl carbon atom.

  

b.Lysine contributes to the base addition in the forward reaction and hence Glutamate is an acid . The converse is true for the reverse reaction.

c. Enolase requires mg as cofactor for its activity .EDTA is a chelating agent and removes the magnesium ion hence loses its activity