1. Consider an enzyme that catalyzes the aldol reaction between dihydroxyacetonephosphate and acetaldehyde in the active site shown below. When the reaction is run in the presence of NaBH3CN, the

enzyme quickly becomes inactivated. a. Draw a mechanism for the reaction involving covalent and general acid/base catalysis. Identify two possible roles served by AA1 (AA1 is not directly involved in catalysis). To which face (re or si) of the enamine intermediate is acetaldehyde added? b. When the reverse reaction is run in D2O, deuterium is incorporated stereoselectively as shown below. Based on this information, which substrate hydrogen is deprotonated in the forward reaction ? (pro-R or pro-S) c. In the forward reaction, does the reaction proceed with inversion or retention at the nucleophillic carbon of the dihydroxyacetonephosphate substrate?

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