Glycogen sequences

This interdependency of GSK-3 with casein kinase II has been defined as hierarchal phosphorylation. Another example of the hierarchal phosphorylation is seen with cyclic-AMP-dependent protein kinase and casein kinase I. The cAMP-dependent protein kinase enhances phosphorylation of the glycogen synthase by casein kinase The phosphorylation by casein kinase I was serine residue Synthetic peptides based on the four phosphoryiated regions in the muscle glycogen sequence (residues 694—707, 706-733, 1-14, and 636-662) were synthesized and phosphoryiated. Casein kinase I could not phosphorylate the unphosphorylated peptides but, if cAMP-dependent kinase phosphoryiated peptides, 694—707, 706-733, and 1-14, all three peptides were easily phosphoryiated by the casein kinase I. The greatest stimulation was seen with peptide 1-14. In the case of peptide... 

Figure 18-7. Control of glycogen synthase in muscle (n = number of glucose residues). The sequence of reactions arranged in a cascade causes amplification at each step, allowing only nanomole quantities of hormone to cause major changes in glycogen concentration. (GSK, glycogen synthase kinase-3, -4, and -5 G6P, glucose 6-phosphate.)...

At this point it is necessary to make a distinction between the meanings of template and primer. The word template refers to the structural sequence of the polymerized monomeric units of a macromolecule that provides the pattern for the synthesis of another macromolecule with a complementary or characteristic sequence. The word primer, on the other hand, refers to a polymeric molecule that contains the growing point for the further addition of monomeric units. Glycogen is an example of a primer to which glucose units are added however, glycogen has no template activity. 

Panswad T, Iamsamer K, Anotai J (2001) Decolorization of azo reactive dye by polyphosphate and glycogen accumulating organisms in an anaerobic aerobic sequencing batch reactor. Bioresour Technol 76 151-159... 

The next key point is to realize that each enzyme in the pathway exists in both active and inactive forms. cAMP initiates a cascade of reactions by activating protein kinase A (PK-A)," the active form of which activates the next enzyme in the sequence, and so on. At the end of the day, glycogen phosphorylase is activated and glucose or ATP is produced. This signaling pathway is a marvelous amplification system. A few molecules of glucagon or adrenaline may induce formation of many molecules of cAMP, which may activate many of PK-A, and so on. The catalytic power of enzymes is magnified in cascades of this sort. 

To help to understand this process, it is useful to appreciate that there is a degree of similarity in the sequences of the three major synthetic processes, glycogen, fatty acid and peptide syntheses. The similarities are presented in Table 6.2. 

In the ebb phase, there is increased activity of the sympathetic nervous system and increased plasma levels of adrenaline and glucocorticoids but a decreased level of insulin. This results in mobilisation of glycogen in the liver and triacylglycerol in adipose tissue, so that the levels of two major fuels in the blood, glucose and long-chain fatty acids, are increased. This is, effectively, the stress response to trauma. These changes continue and are extended into the flow phase as the immune cells are activated and secrete the proinflammatory cytokines that further stimulate the mobilisation of fuel stores (Table 18.2). Thus the sequence is trauma increased endocrine hormone levels increased immune response increased levels of cytokines metabolic responses. 

Covalent interconversion of enzymes is well established as a fundamental theme in metabolic regulation. The prototypic reversible interconverting systems include the sequence of phosphorylation/dephosphorylation steps in the activation of mammalian glycogen phosphorylase and pyruvate dehydrogenase as well as the nucleotidyla-tion/denucleotidylation using UTP and ATP in the bacterial glutamine synthetase cascade (see Fig. 1.). 

A metabolite, molecular entity, or some other event/ process that precedes another component in a longer sequence of events or conversions. For example, the isoprenoid metabolite squalene is a precursor of cholesterol and glucose 6-phosphate is a precursor of glycogen, ribose, and pyruvate. See Series First Order Reaction Pulse-Chase Experiments... 

Write a balanced fermentation sequence by which glycogen can be converted rapidly to sn-glycerol 3-phosphate and pyruvate in insect flight muscle. How many molecules of ATP per glucose unit of glycogen will be formed ... 

A metabolite acting as an allosteric effector turns on an enzyme that either acts directly on that metabolite or acts on a product that lies further ahead in the sequence. For example, in Fig. 11-1, metabolite C activates the enzyme that catalyzes an essentially irreversible reaction of compound D. An actual example is provided by glycogen synthase, whose inactive "dependent" or D form is activated allosterically by the glycogen precursor glucose 6-phosphate.39 See also phosphorylase kinase (Section 2). 

We have already considered regulatory cascades initiated respectively by the (3 and a2 adrenergic receptors. The effect of these cascades on glycogen phos-phorylase is outlined on the left side of Fig. 11-4. One branch of the cascade sequence begins with release of... 

Relationships in glycolysis and gluconeogenesis. Points at which ATP is produced or consumed are indicated. Compounds in the same metabolic pools are indicated by purple boxes. Three small pseudocycles (la, II, III) in the paired sequences occur between glycogen and pyruvate, or between glycogen and glucose (lb, II, III). Only enzymes that are unique to either glycolysis or gluconeogenesis are indicated (screened in blue). 

S. Yu, K. Bojsen, B. Svensson, and J. Marcussen, a-l,4-Glucan lyases producing 1,5-anhydro-D-fructose from starch and glycogen have sequence similarity to a-glucosidases, BBA Protein Struct. Mol. Enzym., 1433 (1999) 1-15, review, 53 references. 

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