PSK is a proteoglycan concentrate prepared commercially by hot-water extract of cultured mycelia from the edible mushroom Trametes versicolor (Coriolus versicolor, Polystictus versicolor.) The mushroom is also known by the common names of Kawaratake (Japan), Yun-Zhi (China) and Turkey tail (Europe and America).
The substance isolated from Coriolus versicolor by hot-water extraction shares similar characteristics with an active proteoglycan compound known in Japan as PSK (polysaccharopeptide-Krestin) in terms of chemical composition and structure. A chemically similar compound known as PS-P (Polysaccharide-Peptide) is isolated from a Chinese strain of the same mushroom. PSK is used as a generic term for PS-Krestin and PS-P.
The compound consists of approximately 35% polysaccharides composed of glucose, mannose, xylose, galactose and fucose and 35% protein consisting mainly of acidic amino acids and lesser of other neutral amino acids1. The polysaccharides are linked to the core protein (hence the name proteoglycan) to give a beta-1,4-glucan configuration with a molecular weight of approximately 100 kilodaltons1,2.