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Publisher Summary This chapter discusses the molecular structure of glycogens. Glycogens, from vertebrate, invertebrate, bacterial, and yeast cells, are multiply-branched molecules (molecular weight ∼10 7 ) consisting of chains of α-(1 → 4)-linked D-glucose residues. The chains that are arranged in a tree- or bush-like form, normally contain an average of about 12 D-glucose residues; 40-50% of these may be removed by β-amylase. The exterior portions of the chains are therefore longer than those in the interior of the molecules, where adjacent branch points are separated by only 3–4 D-glucose residues. Small variations in molecular structure are shown by glycogens from different biological sources. A small proportion of glycogens may be expected to have abnormal structures. In this connection, the isolation of maltulose (some 5 %) from α-amylolytic digest of glycogen of pregnant-rabbit liver would suggest that D-fructose may be an extremely rare but minor component of certain glycogens.

Publisher Summary This chapter discusses the enzyme systems catalyzing the metabolism of starch and glycogen. Recent researches show that as with other polysaccharides, nucleotide intermediates are involved in biosynthesis. Progress in biochemical researches on starch and glycogen may be divided into several phases. Until about 1937, studies were concerned with the descriptive aspects of amylase action, in which soluble starch, the usual substrate, was regarded as “a single polysaccharide.”The second phase followed from the discovery of phosphorylase in animal tissues, of the mechanism of glycogenolysis, and of the first enzymic synthesis of a polysaccharide. Third, with the availability of highly purified and crystalline enzymes, the results of some preliminary investigations on the chemistry of certain enzymic reactions have been reported; and fourth, as a result of further investigations, previous views on the specificity and action pattern of a number of starch-metabolizing enzymes are modified. The enzyme systems in the starch-synthesizing algae and protozoa are largely unknown.