Fig. 4: Proposed catalytic mechanism of PpAAT1. | Horticulture Research

Fig. 4: Proposed catalytic mechanism of PpAAT1.

From: Site-directed mutagenesis identified the key active site residues of alcohol acyltransferase PpAAT1 responsible for aroma biosynthesis in peach fruits

Fig. 4

a Internal esterification reaction using 4-hydroxydecanoyl–CoA as the substrate. (1) His165 is oriented to the carbonyl group, while Asp376 is oriented to the hydroxyl group of 4-hydroxydecanoyl–CoA, (2) the hydrogen atom of the hydroxyl group of 4-hydroxydecanoyl–CoA is transferred to the carboxyl group of Asp376 to form an aromatic nucleus, (3) the carbon–oxygen double bond is formed, and the CoA-SH group is removed from 4-hydroxydecanoyl–CoA, and (4) γ-decalactone is formed. b Esterification reaction using acetyl–CoA and alcohols as substrates. (1) substrates at the catalytic center, (2) the hydroxyl group of alcohols forms a hydrogen bond with His165, (3) a hydrogen atom is transferred to a N atom on His165 and the alcohol substrate forms an O anion to attack the acetyl C atom of acetyl–CoA, (4) the substrates form a C=O double bond and the negatively charged coenzyme A, and (5) an ester is formed and the negatively charged coenzyme A accepts a hydrogen atom from His165 to form coenzyme A

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