The ADP-Glucose Pyrophosphorylase (GlgC) in Synechocystis sp. PCC 6803 catalyzes the first step in glycogen synthesis by converting glucose-1-phosphate into ADP-Glucose, which is added in turn to a growing glycogen chain by glycogen synthases (GlgA1 and GlgA2). Thus far, the in vitro study of GlgC was limited to using malachite green assays for free phosphate, or radiolabel-based methods1. With this work, we present our efforts in developing an in vitro continuous assay coupling GlgA1 to the GlgC reaction, simulating the process of glycogen synthesis in vivo. We also demonstrate the screening of selected metabolites and their effects on GlgC activity. We also describe in further detail the interplay between the activator and inhibitor of GlgC, 3-PGA and phosphate respectively. This new coupled glycogen assay could serve as a useful modelling tool to enable further kinetic studies on the glycogen synthesis pathway and its key players.

Iglesias, A. A., Kakefuda, G. & Preiss, J. Regulatory and Structural Properties of the Cyanobacterial ADPglucose Pyrophosphorylases. Plant Physiol. 97, 1187–1195 (1991).