Starch synthesis

Glucose must be taken up by the cells and synthesised first into glycogen and then starch.

Genes

Figure 1' E. colis native glycogen synthesis pathway. In blue is glgC, a gene which we have mutated to a more active form.

Glycogen synthesis

E. coli and B. subtilis are natively able to synthesise glycogen from starch (see Figure 1 for E. coli's native pathway). However, we want to upregulate this pathway. The gene glgC (ADP-glucose pyrophosphorylase, catalysing the convertion glucose 1-phosphate and ATP to ADP-glucose and PPi) is responsible for the most rate-limiting step of glycogen synthesis in E. coli. This is because the protein is negatively regulated by 5'-AMP, ADP or orthophosphate. The glgC16 mutant has the substitution G336D to glgC, and has been reported to increase the yield of glycogen. This is due in part to the loss of allosteric inhibition and is also due to increased activity in the absence of its activator molecule, fructose 1,6 bis-phosphate.