Glycogen content of eggs and embryos of Arbacia punctulata

Abstract

The presence of glycogen in Arbacia punctulata embryos was determined after alkaline extraction by a specific assay utilizing crystalline glycogen phosphorylase and amylo-1,6-glucosidase. Mature unfertilized eggs contain an average 23.4 μg of glycogen per milligram of protein. Glycogen reserves are maintained after fertilization through the blastula stage thus are not utilized as the primary energy source for early development. At gastrulation there is a drop to an average 14.8 μg of glycogen per milligram of protein. The polysaccharide may contribute significantly to the energy pool at this stage. Glycogen was isolated from mature ova and prepared for electron microscopy. The negatively stained molecules are single particles 300–400 Å in diameter. Glycogen pools are not inert during development. Growing embryos were cultured in the presence NaH 14CO 3. Incorporation of isotope into glycogen was observed from the 2-cell stage onward. By blastula, glycogen- 14C accounted for 18% of the total radioactivity incorporated. Glycogen phosphorylase (pH optimum 7.3) is present in unfertilized eggs and morulae. The enzyme in both in vitro systems is capable of getting rid of all the egg's glycogen within 1 hr. Lack of exogenous AMP reduces phosphorylase activity by 50% in enzyme preparations of unfertilized eggs.