Glycogen Synthetase of Bee Larvae

During the larval stage of the honeybee there is an abrupt and very large elevation of glycogen content. Homogenates from larvae of high glycogen content have an active glycogen synthetase that is associated with the particulate glycogen fraction. Although the enzyme resembles mammalian glycogen synthetase in many of its properties there is at least one important difference. The enzyme bound with particulate glycogen of bee larvae, but not of mammals, is an active enzyme-substrate complex, since high rates of glucose incorporation are observed in the absence of added soluble primer. The main factor limiting incorporation of glucose into glycogen under the conditions of these experiments seems to be the length of outer branch chains in the primer. When this limit is reached, incorporation stops. Addition of glucose 6-phosphate causes incorporation to resume until a higher limit is attained. Two alternative interpretations of this effect are possible. Glucose 6-phosphate either changes the specificity of the enzyme for primer outer chains or activates a glucose 6-phosphate-dependent form of the enzyme that can utilize longer outer chains as effective priming units.