The enzyme dihydroneopterin aldolase (DHNA) is found in the metabolic pathway leading to folic acid. The enzyme catalyzes the reaction
below, the conversion of 7,8-dihydroneopterin (DHNP) to 6-hydroxymethyl-7,8-dihydropeterin (HP) and glycoaldehyde (GA), the third step
in the biosynthetic path to folic acid. The enzyme also catalyzes the epimerization of 7,8-dihydroneopterin to 7,8-dihydro-L-monopterin
(DHMP). Provide a chemical mechanism that can account for the formation of both of these products. Be sure to show the involvement of
enzyme residues that might facilitate each step in the mechanism.
