Abstract
Glycogen synthase, glycogen phosphorylase, glucose‐6‐phosphate dehydrogenase, 6‐phosphogluconate dehydrogenase, and glucose‐6‐phosphatase were determined for the first time in the accessory lobes of Lachi from late embryonic chicks. The activities of these enzymes were compared with those found in other glycogen‐metabolizing tissues, specifically the glycogen body, liver, and skeletal muscle, obtained from the same embryos. The data show that, as in the glycogen body, the accessory lobes of Lachi lack glucose‐6‐phosphatase, but contain relatively high activity levels of glycogen synthase I, total and active glycogen phosphorylase, and the dehydrogenases of glucose‐6‐phosphate and 6‐phosphogluconate. The percent of glycogen synthase I activity in the Lachi lobes is from two‐ to 20‐fold greater than that observed in the glycogen body, liver, or muscle, whereas the percent of glycogen phosphorylase a activity is comparable to that of the liver, but greater than that in the glycogen body or muscle. The activity of each dehydrogenase of the pentose phosphate cycle in the Lachi lobes is similar to that noted in the glycogen body, but is over two‐ or fivefold greater than that activity found in muscle or liver. Our data, together with other recent evidence, suggest that the role of glycogen in these functionally enigmatic tissues may be to support the precocious process of myelin synthesis in the developing bird, as well as possibly to provide alternate sources of energy for the avian central nervous system.