Enolization of dihydroxyacetone

This cleavage is a retro-aldol reaction. It is the reverse of the process by which D-fructose 1,6-diphosphate would be formed by addition of the enolate of dihydroxyacetone phosphate to D-glyceraldehyde 3-phosphate. The enzyme aldolase catalyzes both the... 

Another group of sugar epimerases, which uses a metal cofactor instead of NADH/NAD+, takes an entirely different approach to epimerization. L-ribulose 5-phosphate 4-epimerase, which is involved in the bacterial metabolism of arabinose, performs a retro-aldol cleavage of a C-C bond to yield a metal-stabilized enolate of dihydroxyacetone and glycoaldehyde phosphate, similar to the reaction catalyzed by class II aldolases [77-79]. The glycoaldehyde phosphate is thought to rotate, such that addition of the enolate generates the isomeric product. 

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