Control of glycogen metabolism in the developing turkey poult

An experiment was conducted with young turkey poults to evaluate factors controlling glycogen metabolism in the period following hatching. Glucose and sucrose solutions were given along with a standard starter diet. Liver and carcass glycogen were measured on days 1, 4 and 6. Liver glycogen synthetase (EC 2.4.1.21) and phosphorylase (EC 2.4.1.1) were also assayed at these times. The characteristics of active and inactive glycogen synthetase at these times were determined and sensitivity of the active and inactive forms were related to physiological concentrations of glucose-6-phosphate. Supplemental glucose or sucrose increased carcass glycogen in comparison to controls; however, but sucrose was more effective than glucose in promoting liver glycogen synthesis in 4- and 6-day-old poults. There was an age dependent increase in carcass glycogen between days 1 and 6, but a decrease in liver glycogen between days 4 and 6. The activation of liver glycogen synthetase is incomplete in 1 day old poults but activity increases during the 1st week of life. Activation of glycogen synthetase decreased the apparent Ka for glucose-6-phosphate. Phosphorylase inactivation in vitro was not affected by age. Liver glucose-6-phosphate increases rapidly after hatching and the concentration is related to the in vitro Ka derived for both active and inactive synthetases. Both glucose and sucrose increased liver glucose-6-phosphate at days 4 and 6 as well as glycogen synthetase activity. The increase in enzyme activity may be caused indirectly by an allosteric effect of glucose-6-phosphate. Phosphorylase, while not affected by supplemental carbohydrates, did decrease in activity between days 4 and 6. The decrease in activity could affect the phosphorylase a/ synthetase a ratio and change glycogen metabolism.