Glycogen metabolism in the developing chick glycogen body: Functional significance of the direct oxidative pathway

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Abstract
Glucose‐6‐phosphate dehydrogenase, 6‐phosphogluconate dehydrogenase, and glucose‐6‐phosphatase were quantitatively determined for the first time in glycogen body tissue from late embryonic and neonatal chicks. For comparative purposes, the activities of these enzymes were examined also in liver and skeletal muscle from pre‐ and post‐hatched chicks. The present data show that both the embryonic and neonatal glycogen body lack glucose‐6‐phosphatase, but contain relatively high levels of glucose‐6‐phosphate dehydrogenase and 6‐phosphogluconate dehydrogenase. The activity of each dehydrogenase in either embryonic or neonatal glycogen body tissue is two‐ to five‐fold greater than that found in muscle or liver from pre‐ or post‐hatched chicks. The relatively high activities observed for both dehydrogenases in the glycogen body, together with the absence of glucose‐6‐phosphatase activity in that tissue, suggest that the direct oxidative pathway (pentose phosphate cycle) of glucose metabolism is a functionally significant route for glycogen utilization in the glycogen body. It is hypothesized that the glycogen body is metabolically linked to lipid synthesis and myelin formation in the central nervous system of the avian embryo.