Гликоген

Химические свойства

White to off-white powder

Использование

glycogen is a skin-conditioning agent. It is a high molecular-weight polymer distributed through the cell protoplasm.

Определение

A polysaccharide that is the main carbohydrate store of animals. It is composed of many glucose units linked in a similar way to starch. Glycogen is readily hydrolyzed in a stepwise manner to glucose itself. It is stored largely in the liver and in muscle but is found widely distributed in the body.

Общее описание

Glycogen is a branched polymer of glucose synthesized by animal cells for energy storage and release. It is constructed of predominantly α1→4 glycosidic bonds with branches created through α1→6 glycosidic bonds.

Синтез

Glycogen synthesis occurs in the cytoplasm and can be divided into the following four steps:
(1) Glycogenesis begins with the phosphorylation of glucose by glucokinase in the liver and by hexokinase in muscle and other tissues.
(2) Glucose-6-phosphate is then converted into glucose-1-phosphate by phosphoglucomutase, a reaction similar to that catalysed by phosphoglycerol mutase.
(3) Glucose-1-phosphate is converted into uridine diphosphate (UTP)-glucose, the immediate precursor of glycogen synthesis, by reaction with uridine triphosphate (UTP). This reaction is catalysed by glucose 1-phosphate uridylyltransferase (or UDP-glucose pyrophosphorylase).
(4) Finally, the glucosyl residue at the C-1 position of UDP-glucose is added to the tyrosyl group at position 194 of glycogen protease in an Mg2+-dependent autocatalytic reaction. Glycosidases similarly extend the glucan chain by α(1→4) glycosidic bonds by adding 6 to 7 glucosyl units, using UDP-glucose as the substrate, in an autocatalytic reaction. The glucan primer of glycogen proteins is elongated by glycogen synthase using UDP glucose. Initially, the glycogenin primer and glycogen synthase are strongly bound using a 1:1 complex. As the dextran chain grows, glycogen synthase separates from glycogen.

Методы очистки

A 5% aqueous solution (charcoal) of D(+)-glycogen is filtered, and an equal volume of EtOH is added. After standing overnight at 3o the precipitate is collected by centrifugation, washed with absolute EtOH, then EtOH/diethyl ether (1:1) and diethyl ether, and dried. [Sutherland & Wosilait J Biol Chem 218 459 1956.]