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From this discussion of the hormonal regulation of glycogen metabolism. Read this material and summarize in no more than one page. Use figures and frame your narrative in terms of the picture. No resources other than the text are required or desirable.

From this discussion of the hormonal regulation of glycogen metabolism. Read this material and summarize in no more than one page. Use figures and frame your narrative in terms of the picture. No resources other than the text are required or desirable.

Biochemistry
Biochemistry
9th Edition
ISBN:9781319114671
Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Chapter1: Biochemistry: An Evolving Science
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 From this discussion of the hormonal regulation of glycogen metabolism. Read this material and summarize in no more than one page. Use figures and frame your narrative in terms of the picture. No resources other than the text are required or desirable. 

Hormonal Regulation of Glycogen Metabolism Reciprocal regulation of glycogen metabolism by allosteric control and hormone signaling is a good example of how intracellular signaling pathways control biochemical processes through reversible phosphorylation. The graphs in Figure 14.41 show that when glucose is added to a freshly prepared liver cell extract, glycogen phosphorylase activity rapidly decreases, while glycogen synthase activity steadily increases. This mechanism of reciprocal regulation occurs on a timescale of minutes and is the result of allosteric inhibition of glycogen phosphorylase activity by glucose (see Figure 14.33) and allosteric activation of glycogen synthase activity by glucose-6-P (see Figure 14.39). We now examine more closely how glucagon and insulin regulate these same two enzymes on a timescale of several hours, which is needed for homeostatic control of blood glucose levels before and after a meal. Glycogen phosphorylase activity (% of total) 100 80 60 40 20 0 10 20 30 40 100 80 60 40 20 0 Glycogen synthase activity (% of total) Time after adding glucose to liver cell extract (min) Figure 14.41 Glucose addition to liver cell extracts results in rapid allosteric inhibition of glycogen phosphorylase activity and, at the same time, allosteric activation of glycogen synthase activity. This mechanism of reciprocal regulation occurs on a timescale of minutes and reflects a sudden increase in blood glucose levels in response to ingesting a carbohydrate-rich meal. BASED O J. MASSILLON ET AL. (1995). DEMONSTRATION OF A GLYCOGEN/GLUCOSE 1-PHOSPHATE CYCLE IN HEPATOCYTES FROM FASTED RATS. SELECTIVE INACTIVATION OF PHOSPHORYLASE BY 2-DEOXY-2-FLUORO-ALPHA-D- GLUCOPYRANOSYL FLUORIDE. JOURNAL OF BIOLOGICAL CHEMISTRY, 270, 19351-19356.
Transcribed Image Text:Hormonal Regulation of Glycogen Metabolism Reciprocal regulation of glycogen metabolism by allosteric control and hormone signaling is a good example of how intracellular signaling pathways control biochemical processes through reversible phosphorylation. The graphs in Figure 14.41 show that when glucose is added to a freshly prepared liver cell extract, glycogen phosphorylase activity rapidly decreases, while glycogen synthase activity steadily increases. This mechanism of reciprocal regulation occurs on a timescale of minutes and is the result of allosteric inhibition of glycogen phosphorylase activity by glucose (see Figure 14.33) and allosteric activation of glycogen synthase activity by glucose-6-P (see Figure 14.39). We now examine more closely how glucagon and insulin regulate these same two enzymes on a timescale of several hours, which is needed for homeostatic control of blood glucose levels before and after a meal. Glycogen phosphorylase activity (% of total) 100 80 60 40 20 0 10 20 30 40 100 80 60 40 20 0 Glycogen synthase activity (% of total) Time after adding glucose to liver cell extract (min) Figure 14.41 Glucose addition to liver cell extracts results in rapid allosteric inhibition of glycogen phosphorylase activity and, at the same time, allosteric activation of glycogen synthase activity. This mechanism of reciprocal regulation occurs on a timescale of minutes and reflects a sudden increase in blood glucose levels in response to ingesting a carbohydrate-rich meal. BASED O J. MASSILLON ET AL. (1995). DEMONSTRATION OF A GLYCOGEN/GLUCOSE 1-PHOSPHATE CYCLE IN HEPATOCYTES FROM FASTED RATS. SELECTIVE INACTIVATION OF PHOSPHORYLASE BY 2-DEOXY-2-FLUORO-ALPHA-D- GLUCOPYRANOSYL FLUORIDE. JOURNAL OF BIOLOGICAL CHEMISTRY, 270, 19351-19356.
Figure 14.42 summarizes the phosphorylation status and enzymatic activity of glycogen phosphorylase and glycogen synthase in liver cells as a function of glucagon and insulin signaling. When blood glucose levels are low, glucagon signaling initiates a phosphorylation cascade via protein kinase A, which directly phosphorylates and inhibits glycogen synthase. Glycogen phosphorylase activation by glucagon signaling involves a downstream signaling protein called phosphorylase kinase, which is phosphorylated by protein kinase A. Activated phosphorylase kinase then phosphorylates glycogen phosphorylase to initiate glycogen degradation. The net result of glucagon signaling in liver cells is increased rates of glycogen degradation and glucose export. Low blood glucose levels Glucagon P 10.00 www Net phosphorylation Phosphorylase kinase Protein kinase A Glucagon receptor Active glycogen Inactive glycogen phosphorylase synthase - GLUT2 P Glycogen degradation Glucose Glucose export P High blood glucose levels Insulin Net dephosphorylation Protein phosphatase 1 Inactive glycogen Active glycogen phosphorylase synthase 00 Insulin receptor но- GLUT2 Glycogen synthesis Glucose Glucose import -OH Figure 14.42 Delayed hormonal regulation of glycogen metabolism in liver cells is mediated by phosphorylation and dephosphorylation of glycogen phosphorylase and glycogen synthase, respectively. Glucagon signaling stimulates protein kinase A activity, leading to net phosphorylation of glycogen phosphorylase and glycogei synthase. The downstream response to glucagon signalin in liver cells is glycogen degradation and glucose releas Insulin signaling stimulates protein phosphatase 1 activit and promotes net dephosphorylation of glycogen phosphorylase and glycogen synthase. The downstream response to insulin signaling in liver cells is glycogen synthesis and glucose import.
Transcribed Image Text:Figure 14.42 summarizes the phosphorylation status and enzymatic activity of glycogen phosphorylase and glycogen synthase in liver cells as a function of glucagon and insulin signaling. When blood glucose levels are low, glucagon signaling initiates a phosphorylation cascade via protein kinase A, which directly phosphorylates and inhibits glycogen synthase. Glycogen phosphorylase activation by glucagon signaling involves a downstream signaling protein called phosphorylase kinase, which is phosphorylated by protein kinase A. Activated phosphorylase kinase then phosphorylates glycogen phosphorylase to initiate glycogen degradation. The net result of glucagon signaling in liver cells is increased rates of glycogen degradation and glucose export. Low blood glucose levels Glucagon P 10.00 www Net phosphorylation Phosphorylase kinase Protein kinase A Glucagon receptor Active glycogen Inactive glycogen phosphorylase synthase - GLUT2 P Glycogen degradation Glucose Glucose export P High blood glucose levels Insulin Net dephosphorylation Protein phosphatase 1 Inactive glycogen Active glycogen phosphorylase synthase 00 Insulin receptor но- GLUT2 Glycogen synthesis Glucose Glucose import -OH Figure 14.42 Delayed hormonal regulation of glycogen metabolism in liver cells is mediated by phosphorylation and dephosphorylation of glycogen phosphorylase and glycogen synthase, respectively. Glucagon signaling stimulates protein kinase A activity, leading to net phosphorylation of glycogen phosphorylase and glycogei synthase. The downstream response to glucagon signalin in liver cells is glycogen degradation and glucose releas Insulin signaling stimulates protein phosphatase 1 activit and promotes net dephosphorylation of glycogen phosphorylase and glycogen synthase. The downstream response to insulin signaling in liver cells is glycogen synthesis and glucose import.
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