GlyceraIdehyde-3-phosphate

An indirect enzymatic pathway for the formation of uctose-6-phosphate from fructose-l-phosphate has recently been described by Leuthardt et al. Fructose-l-phosphate is cleaved to D-glyceraldehyde and dihydroxyacetone phosphate. The latter isomerizes to form glyceraldehyde-3-phosphate. The triose phosphates condense to fructose-1,6-diphosphate which is dephosphorylated at the 1 position. In the presence of ATP, the glyceraldehyde may be converted by means of a triosekinase to glyceraIdehyde-3-phosphate. 

Figure 3 Formation of deoxyxylulose phosphate 11 (DXP) from pyruvate 9 and glyceraidehyde phosphate 10 by the DXP synthase.

Several aspects of the MEP pathway reaction sequence are unexpected, including the conversion of two highly oxidized carbohydrate derivatives, pyruvate 9 and glyceraidehyde phosphate 10 (GAP), into two monounsaturated alcohol diphosphates, IPP 7 and DMAPP 8 (Fig. 2). 

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