stonefield
Forum Newbie
Topics: 4
Posts: 5
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I have a question about the glycogen synthases. There are two forms of glycogen synthases; form a and form b. I understand that Glycogen synthase a is an active form and glycogen synthase b is an inactive form, so when you have glycogen synthase a, it means you are making more glycogen and when you have glycogen synthase b, it means you are making more glucose, correct? From the diagram I attached with this post, I am not sure what dertermines to make more glycogen and what dertermines to make more glucose (via G1P). i also don't understand "phosphorylation of glycogen phosphatase" Does it mean shifting to glycogen synthase a or b??? Thanks.
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| blueocean
Forum Senior
Topics: 15
Posts: 195
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PKA is cAMP-dependent protein kinase. PPI-1 is phosphoprotein phosphatase-1 inhibitor. Whether a factor has positive (+ve) or negative (-ve) effects on any enzyme is indicated. Briefly, glycogen synthase a is phosphorylated, and rendered much less active and requires glucose-6-phosphate to have any activity at all. Phosphorylation of glycogen synthase is accomplished by several different enzymes. The most important is synthase-phosphorylase kinase the same enzyme responsible for phosphorylation (and activation) of glycogen phosphorylase. PKA (itself activated through receptor mediated mechanisms) also phosphorylates glycogen synthase directly. The effects of PKA on PPI-1 are the same as those described above for the regulation of glycogen phosphorylase. The other enzymes shown to directly phosphorylate glycogen synthase are protein kinase C (PKC), calmodulin-dependent protein kinase, glycogen synthase kinase-3 (GSK-3) and two forms of casein kinase (CK-I and CK-II). The enzyme PKC is activated by Ca2+ ions and phospholipids, primarily diacylglycerol, DAG. DAG is formed by receptor-mediated hydrolysis of membrane phosphatidylinositol bisphosphate (PIP2).
Attached Files:
glycogensynthaseregulation.gif (8 KB, 12 downloads)
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| stonefield
Forum Newbie
Topics: 4
Posts: 5
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Thank you for your very quick reply. It helped a lot to understand what is going on in thid diagram. One more thing to summarize this diagram, to activate Glycogenolysis, PKA is stimulated and shift to glycogen synthase b, right? And to inactivate the glycogenesis, PPI-1 inhibit the phosphoprotein phosphatase so it shifts to glycogen synthase a. Also, it is interesting that the same PKA activate and inactivate this process. Thank you.
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