Glycogen intermediates

Glycogen content phosphoryla tion Low phosphorylation glycolysis Intermediate High... 

Di-tt-octylphthalate has been shown to be a mild liver toxin at high doses in acute- and intermediate-duration studies in rodents. While the mechanism of action for these hepatic effects is not known, di-w-octylphthalate does not appear to behave like other phthalate esters such as di(2-ethylhexyl)phthalate, which have been shown to be hypolipidemic peroxisome proliferators. Instead, the liver changes associated with exposure to di- -octylphthalate are characterized by marked centrilobular accumulation of fat and loss of glycogen, accompanied by reduced glucose-6-phosphatase activity and some centrilobular necrosis. 

A positive AG for this reaction conld also be achieved by a marked decrease in the concentration of glucose 6-phosphate. Why is this not feasible Glucose 6-phosphate is an important metabolic intermediate and is involved in several metabolic pathways (e.g. glycogen synthesis, glycolysis, pentose phosphate pathway). Lowering its concentration by the two orders of magnitude, which would be necessary, would markedly decrease the rates at which these important pathways could proceed. 

In contrast to glucagon, the peptide hormone insulin (see p. 76) increases glycogen synthesis and inhibits glycogen breakdown. Via several intermediates, it inhibits protein kinase GSK-3 (bottom right for details, see p. 388) and thereby prevents inactivation of glycogen synthase. In addition, insulin reduces the cAMP level by activating cAMP phosphodiesterase (PDE). 

The stem cells of the basal cells are located at the level of the limbus, which come from centripetal migration. The daughter cells migrate to form the intermediate cells. Their cytoplasm, which is rich in glycogen and mitochondria, shows their high metabolic activity. It also contains a Golgi s apparatus, some microtubules, and some keratin filaments connected to each other by desmosomes and hemidesmo-somes. Most of all this cytoplasm contains some actin... 

Note All these amino acids are precursors of blood glucose or liver glycogen, because they can be converted to pyruvate or citric acid cycle intermediates. Of the 20 common amino acids, only leucine and lysine are unable to furnish carbon for net glucose synthesis. These amino acids are also ketogenic (see Fig. 18-21). 

In this chapter we look at mechanisms of metabolic regulation, using the pathways in which glucose is an intermediate to illustrate some general principles. First we consider the pathways by which glycogen is synthesized and broken down, a very well-studied case of meta-... 

Malonyl-CoA, the first intermediate in the cytosolic biosynthesis of long-chain fatty acids from acetyl-CoA (see Fig. 21-1), increases in concentration whenever the animal is well supplied with carbohydrate excess glucose that cannot be oxidized or stored as glycogen is converted in the cytosol into fatty acids for storage as triacylglycerol. The inhibition of carnitine acyltrans-ferase I by malonyl-CoA ensures that the oxidation of... 

---