   4.2.99.22 | 6-tuliposide A = tulipalin A + D-glucose |
putative reaction mechanism of TCE enzymes, overview. The reaction begins with a nucleophilic attack by the catalytic Ser, whose hydroxyl group is activated by the charge relay of the catalytic triad, on the carbonyl carbon of 6-Pos. This is followed by the formation of a tetrahedral intermediate, which is stabilized by the oxyanion hole structure contributed by the two Gly residues of the HGG motif. Then, following the elimination of glucose, the acyl-enzyme complex is formed, and an intramolecular nucleophilic attack by a terminal hydroxyl group of 6-Pos, but not by water, occurs. This nucleophilic attack results in the formation of the five-membered ring structure of Pa. If the acylenzyme complex is subjected to a nucleophilic attack by activated water, then gamma-hydroxy acids are released as hydrolytic products, but this process never occurs in the TCE reactions |
747322 |
