Glycogen characterization

Glycogenosis type IV (branching enzyme deficiency) results in the formation of a variant of glycogen, characterized by abnormally long inner and outer glucosyl chains and fewer branch points than normal. The abnormal variant is stored in sufficient amounts to cause some vacuolation. The clinical manifestations of this... 

Fig. 1. Primary stmctures of some common polysaccharides, (a) Alpha-glycoside linkages characterize amylose, amylopectin, and glycogen (b) cellulose has...

Glycogen storage disease is a generic term to describe a group of inherited disorders characterized by deposition of an abnormal type or quantity of glycogen in the tissues. The principal glycogenoses are summarized in Table 18—2. Deficiencies of adenylyl kinase and cAMP-dependent protein kinase have also been re-... 

The anaerobic metabolism of adult body wall muscle has been well characterized (Komuniecki and Harris, 1995). Large glycogen stores are... 

Shimomura, S., and Fukui, T. (1978) Characterization of the pyridoxal phosphate site in glycogen phos-phorylase b from rabbit muscle. Biochemistry 17, 5359. 

Phosphorylase deficiency (McArdle s disease, glycogenosis type V) is an autosomal recessive myopathy caused by a genetic defect of the muscle isoenzyme of glycogen phosphorylase (Fig. 42-1). Intolerance of strenuous exercise is present from childhood, but usually onset is in adolescence, with cramps after exercise [1, 5]. Myoglobinuria occurs in about one-half of patients. If they avoid intense exercise, most patients can live normal lives however, about one-third of them develop some degree of fixed weakness, usually as a late-onset manifestation of the disease. In a few patients, weakness rather than exercise-related cramps and myoglobinuria characterizes the clinical picture. 

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. 

Important genetic deficiencies, listed in Table 1-14-3, are classed as glycogen storage diseases because all are characterized by accumulation of glycogen in one or more tissues. 

Fig. 2.1L Model of allosteric and covalent activation of glycogen phosphorylase of muscle. The R-form of the subunits are represented by circles, the T-form by squares. The active state of glycogen phosphorylase (GP) is characterized by a high affinity, the inactive state by low affinity for the substrate PI.

Of the protein kinases, protein kinase A is the best investigated and characterized (review Francis and Corbin, 1994). The functions of protein kinase A are diverse. Protein kinase A is involved in the regulation of metabolism of glycogen, lipids and sugars. Substrates of protein kinase A may be other protein kinases, as well as enzymes of intermediary metabolism. Protein kinase A is also involved in cAMP-stimulated transcription of genes that have a cAMP-responsive element in their control region (review Montminy, 1997). An increase in cAMP concentration leads to activation of protein kinase A which phosphorylates the transcription factor CREB at Ser 133. CREB only binds to the transcriptional coactivator CBP in the phosphorylated state and stimulates transcription (see Chapter 1.4.4.2). 

Chen YT, He JK, Ding JH, Brown BI (1987) Glycogen debranching enzyme purification, antibody characterization, and immunoblot analysis of type III glycogen storage disease. Am J Hum Genet 41 1002-1015... 

Professor French was intensely interested in the mechanism of hydrolysis of starch, glycogen, and other polymers of D-glucose by various types of enzymes, and by acids. He was also interested in elucidating the biochemical pathways for the synthesis of these polymers, and in methods for characterization of the compounds, A very clever method for studying the mechanism of an enzyme reaction was introduced in... 

The glycogen debranching enzyme is the first bifunctional eukaryotic enzyme to be reported that consists of a single polypeptide chain. It catalyzes two distinct activities an oligosaccharide frons-glycosylation followed by hydrolysis of an (1—> 6)-linked D-glucosyl unit to liberate free glucose. Physical-chemical and kinetic characterization of this novel bifunctional enzyme is described by Nelson. 

Insulin, a hormone, plays a key role in catalyzing the processes by which glucose (carbohydrates) furnishes energy or is stored in the body as glycogen or fat. The absence of insulin not only interrupts these processes, but produces depression of essential functions and, in extreme cases, even death. Insulin protein is characterized by a high sulfur content in the form of cystine and it is unstable in alkaline solution. 

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