Paramylon

Paramylon is a storage polysaccharide produced by some photosynthetic protists, most notably the unicellular flagellate Euglena gracilis, and by other euglenoids. It functions as an energy reserve that can be mobilized when needed.

Chemically, paramylon is a polymer of glucose units linked primarily by beta-1,3-glycosidic bonds, forming a linear, unbranched glucan. In the cell, paramylon accumulates in cytoplasmic granules called paramylon bodies.

Paramylon is synthesized in the cytoplasm from glucose and related substrates via enzymes that construct beta-1,3-glucan chains; the process uses UDP-glucose as a donor and yields paramylon granules stored in the cell.

During periods of energy demand, paramylon is hydrolyzed by beta-1,3-glucanases to release glucose, which can feed glycolysis and respiration.

Because of its beta-1,3 linkage, paramylon is distinct from starch, which consists of alpha-1,4 and alpha-1,6 linkages, and from cellulose, which has beta-1,4 links. Paramylon is typically insoluble in water and largely resistant to digestion by animal enzymes, with certain microorganisms able to metabolize it.

Paramylon and related beta-1,3-glucans have attracted scientific interest for their biochemical properties and potential immunomodulatory effects, and paramylon derived from Euglena has been explored in research contexts and some nutraceutical applications.