EFFECT OF PHOSPHORYLATION ON THE REACTION-RATE OF UNNATURAL ELECTROPHILES WITH 2-KETO-3-DEOXY-6-PHOSPHOGLUCONATE ALDOLASE

D-Glyceraldehyde is accepted as an electrophile by 2-keto-3-deoxy-6-ph osphogluconate (KDPG) aldolase (EC 4.1.2.14) at 1% the rate of natural substrate, D-glyceraldehyde 3-phosphate. Accordingly, it was expected that addition of a phosphate moiety at C3 or C4 of unnatural aldehyde s would enhance their activity as electrophilic substrates. Furthermor e, phosphate would act as a useful protecting group during synthetic m anipulations of the aldol adduct. A variety of phosphorylated and non- phosphorylated aldehydes were synthesized and evaluated as substrates for KDPG aldolase. Although small variations in reaction rate were obs erved, phosphorylation failed to provide a universal rate enhancement. Evaluation of substrate kinetic parameters revealed that the high rat e of reaction of D-glyceraldehyde 3-phosphate compared to related elec trophiles is entirely due to the efficiency of turnover with little ch ange in binding exhibited among various substrates.