Extraction, isolation and characterisation of phytoglycogen from su-1 maize leaves and grain

Phytoglycogen is a highly branched soluble α-glucan found in plants, particularly those with decreased activity of isoamylase-type starch debranching enzyme, such as sugary-1 (su-1) maize. An improved technique has been designed to extract and isolate phytoglycogen from the grain and leaves of su-1 maize with minimal degradation for structural characterisation. The structures of extracted phytoglycogen samples were analysed using size-exclusion chromatography (SEC, also termed GPC) and transmission electron microscopy (TEM) and compared with the structure of pig liver glycogen. The SEC weight molecular size distributions indicate that the extraction procedure with protease is most effective in obtaining pure phytoglycogen from grain, whereas that without protease at cold temperature followed by purification using a sucrose gradient is more effective for leaf material. The extracted and purified phytoglycogen samples from both grain and leaf contain wide distributions of molecular sizes (analysed by SEC and TEM), with the smallest being “individual” β particles, which collectively form larger α particles; the latter are dominant in the phytoglycogen samples examined here. The results show that phytoglycogen is similar to liver glycogen in both the range of molecular size distribution and in the presence of α particles.