Fatty acids are degraded to acetyl-CoA in fatty-acid metabolism. The enzyme that catalyzes this conversion, acyl-CoA acetyl transferase, contains a nucleophilic thiol group in its active site and catalyzes the following reactions (enzyme = E):

(a) What is species X?

(b) Assuming that acids and bases are provided in the enzyme active site as needed, outline curved-arrow mechanisms for these transformations.

(c) What is the relationship of the first reaction to the Claisen condensation?

Transcribed Image Text:

R-C-CH₂-C-SCOA + HSE X + HSCOA X (an acyl enzyme) + H₂C-C-SCOA acetyl-CoA --SCOA R-C SCOA + HS- E