Glycogen particle

These more mature cell types are incapable of division and are identified by their nuclear morphology, granule content and accumulation of glycogen particles. In a mature neutrophil there are 200-300 granules, with the specific granules being about twice as abundant as azurophilic granules. 

Glycogen particles, although distributed throughout the protozoan, are concentrated in the region where hydrogenosomes are located (Figs. 1, 4b, 14a, 16a,b). 

Figure 21.19. Regulation of Protein Phosphatase 1 (PPl). Phosphorylation of Rqi by protein kinase A dissociates the catalytic subunit from the glycogen particle and hence the PPl substrates. Inhibition is complete when the inhibitor subunit (I) is phosphorylated and binds to PPl to inactivate it.

Figure 22.17. Electron Micrograph of a Peroxisome in a Liver Cell. A crystal of urate oxidase is present inside the organelle, which is bounded by a single bilayer membrane. The dark granular structures outside the peroxisome are glycogen particles. [Courtesy of Dr. George Palade.]...

The ultrastructure of horse platelets is similar to that of human platelets (White et al. 1976). Features include a flattened discoid shape, a circumfiential band of microtubules, an open canalicular system, alpha granules, mitochondria, dense bodies, and glycogen particles. Compared to human platelets, horse dense bodies are analler and alpha granules are larger and stracturally more complex. The serotonin content of horse platelets is similar to that of human platelets. Horse platelet membrane proteins have been evaluated by polyacrylamide gel electrophoresis and glycoprotein llbllfe has been characterized and monoclonal antibodies have been produced (Lipscomb et al. 1995 Pintado et al. 1995). 

Pig platelets have most of the stmctural elements seen in platelets of other species including circumfrential bands of microtubules, an open canalicular system, glycogen particles, and mitochondria. Dense bodies are tare. Dense bodies contain significant amounts ofhistamine. 

Rat and mouse platelets contain circumfiential microtubules, dense bodies, alpha granules, glycogen particles, and an open canalicitlar system. Ultrastmctural features of mouse and rat platelets are similar to that of human platelets. 

Protein phosphatases-1, 2 A, 2B, and 2C occur in mammalian liver and, as in skeletal muscle, possess essentially all of the phosphatase activity toward enzymes and regulatory proteins of glycogen metabolism. In liver, however, the ratios of the activities of phosphatase-2A and 2C to that of phosphatase-1 are seven-fold higher than in muscle. Although protein phosphatase-I sediments with glycogen particles in both tissues, a much smaller fraction is glycogen-associated in liver than in muscle. The specific activity of phosphatase-2B is lower in liver than in muscle. Protein phosphatase inhibitors-1 and 2 have been identified in liver, where they appear to function as they do in muscle. A disinhibitor protein (M. W. 9,000) of liver can block the effects of inhibitors-1 and 2 on phosphatase-1. 

Figure 21.19 Regulation of protein phosphatase 1 (PPl) in muscle takes place in two steps. Phosphorylation of by protein kinase A dissociates the catalytic subunit from its substrates in the glycogen particle. Phosphorylation of the inhibitor subunit by protein kinase A inactivates the catalytic unit of PPl.

The mature PMN contains abundant cytoplasmic granules, only a few mitochondria, a multilobed nucleus, and glycogen particles. In order to elucidate the biochemical behavior of these organized structures, homogenized cells have been submitted to fractionation. 

Blood platelets circulate in the vascular system as discrete discoid-shaped cells approximately 2-3 urn in diameter. Although anucleated, platelets contain mitochondria, glycogen particles... 

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