The iodine binding capacity (IBC) of glycogen is around 0.30% (w/w) at 3 degrees C. The amount of iodine complexed comprises about 12.5% of the mass of glycogen that takes part in the glycogen-iodine (GI) complex formation. This suggests involvement of four iodine atoms for every 25 anhydroglucose units (AGU, C6H10O5). Since the chromophore is due to the I-4 unit within the helix of 11 AGUs, only 44% of the AGUs (11 out of 25) are involved in the complex formation. The heat of formation of the GI complex is around -40 kJ/mol of I-2 bonded. These results suggest remarkable similarities with those of the amylopectin-iodine (API) complex.