In HMG-CoA biosynthesis (Eq. 22.94), the first step is transfer of the acetyl group from acetyl-CoA to a thiol group of HMGCoA synthase, the catalyzing enzyme (5 E in the equations below). The resulting thioester undergoes aldol addition to acetoacetyl-CoA followed by hydrolysis of the enzyme thioester:

Assuming that acids and bases are provided by groups on the enzyme as needed, give a curved-arrow mechanism for each of these reactions.

Transcribed Image Text:

A SCOA acetyl-CoA + + HS E SCOA acetoacetyl-CoA E A + HSCOA 0 HỌ CH, 0 SCOA H₂O HMG-CoA + HS E