Glycogen

Abstract

This branched polyglucose is a storage form of readily available carbohydrate maximally stored in liver and muscle and, to a small extent, in CNS. It consists of main (B) chains and side (A) chains with α-1→4-glucosidie linkages between the glucose molecules except at the points of origin of the side chains where the linkage is an α-1→6-glucosidic one (see e.g. Manners, 1968). It is readily hydrolysed in liver to glucose to maintain blood levels but, in muscle and CNS, glycogenolysis provides energy for local use only. It has traditionally been regarded by Biochemists as present in both “lyo” and “desmo” forms. The “lyo” form is that part which is extractable with cold trichloracetic acid, while the “desmo” form is that part which is not; the latter, however, is extractable with potassium hydroxide (Wanson and Drochmans, 1968; Leske and Mayersbach, 1969). Isolation of particulate glycogen from various sources was first achieved by Lazarow (1942). He demonstrated various size particles depending on the source but generally falling within two categories; this categorization is recognized now. There are large particles termed α-particles, with an average diameter of 1000 Å— i.e. almost visible by light microscopy—and molecular weight of 100–400 × 10⁶; and smaller ones, termed β-particles, with an average diameter of 300–400 Å and molecular weight of 4–10 × 10⁶ (Revel, 1964; Drochmans and Dantan, 1968; Childress et al., 1970; Smitherman et al., 1972).