NUTR 470 1st Edition Lecture 5 Current Lecture• Gluconeogenesis• Gluconeogenesis (GNG) is the biosynthesis of new glucose.• FBPase catalyzes a rate-determining step of GNG.• F-2,6-P2 is the most powerful inhibitor of FBPase.• FBPase: fructose-1,6-bisphosphatase• GNG is the generation of GLUCOSE whereas G6P-genesis is the generation of G6P.• Muscle does not have G6Pase— primarily in the liver• G6Pase controls the rate of glucose production• when an enzyme lacks the production of this enzyme, kids will have growth problems, specifically brain development and retardation occurs• Physiological Role of GNG• GNG provides glucose when sufficient carbohydrate is not available• GNG is crucial for maintaining glucose homeostasis• Glucose generated from GNG is necessary for the nervous system• G6P-genesis provides G6P that can be used for glycogen synthesis (indirect pathway)• important process to generate glucose• When glucose production is too high, result is diabetes• Place of GNG• GNG in the liver• The liver produces glucose. Under fasted conditions, the liver contributes to ~90% of total glucose production.• Kidney and small intestine• GNG in kidney and small intestine makes limited contributions to the total glucose production. because of the G6P• Other tissues and organs• G6P-genesis provides G6P that can be used for glycogen synthesis (indirect pathway), as well as other metabolic pathways.• Why G6P-genesis, but not GNG?• Glucose-6-phosphatase is present only in the liver and kidney (may also be present in small intestine).• Glucose metabolites• when oxygen is not enough, pyruvate is converted to lactateThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.• cori cycle does not provide enough for gluconeogenesis— must meet needs else way• Carbon Source for GNG• Oxaloacetate• Product of glucogenic amino acids• Glycerol• Product of lipid hydrolysis• Conversion of glycerol to glycerol-3-phosphate is catalyzed by glycerol kinase.• Gneration of oxaloacetate• From pyruvate• Pyruvate carboxylase• From citrate• Generation of malate from citrate• Conversion of malate to OAA•• Generation of Phosphoenolpyruvate• Conversion of OAA to phosphoenolpyruvate is a key regulatory reaction of GNG• what is the first enzyme? PEP CK— phosphoenolpyruvate carboxykinase• The first rate determining step of gluconeogenesis ? this step with PEP• Reaction (on slide)— GTP is formed in TCA cycle through substrate level phosphorylation• Generation of Phosphoenolpyruvate• Phosphoenolpyruvate carboxykinase (PEPCK) is a key regulatory enzyme of GNG• PEPCK• PEPCK is at high abundance in the liver.• first rate determining step of gluconeogenesis• Glucagon and epinephrine stimulate the expression of PEPCK.• when hungry increased levels of glucagon• also a stress condition• need glucose as a source for the brain especially during stressed conditions• Insulin inhibits the expression of PEPCK.• Reduction in the levels of glucose stimulates the expression of PEPCK.• Generation of Frucose-6-phosphate• Conversion of fructose-1,6-bisphosphate into fructose-6-phosphate is a rate-determining step of GNG.• Reminder: • always write down full names • first part of the name tells your the substrate, second part tells you whats happening• Frucose-1,6-phosphatase• FBPase is a key gluconeogenic enzyme• Allosteric inhibitor• Fructose-2,6-bisphosphate• AMP• Small molecule compounds• Targeting FBPase to inhibit GNG is a way to treating diabetes• The Role of Fructose-2,6-bisphosphate• Fructose-2,6-bisphosphate is the most powerful inhibitor of fructose-1,6-bisphosphatase.• Enzyme• 6-phosphofructo-2-kinase• Reaction• F-6-P → Fructose-2,6-bisphosphate• Production of Glucose • Conversion of glucose-6-phosphate into glucose is the final step of gluconeogenesis. • Enzyme • Glucose-6-phosphatase • Reaction • G-6-P —> Glucose + Pi • Location • ER — endoplasmic reticulum• Regulation of Glucose-6-phosphatase• Stimulation of gene expression• Epinephrine, glucagon• Glucocorticoid• Glucose• Suppression of gene expression• Insulin• Small molecule inhibitors• Allosteric inhibition• Regulation of GNG: Role of Glucose• Glucose, serving as an important nutritional signal, is crucial for the regulation of GNG.• Effect on PEPCK• Glucose, at high levels, suppresses the expression of PEPCK in liver cells.• decreased PEPCK activity leads to decreased Gluconeogensis• Effect on glucose-6-phosphatase• Glucose paradoxically stimulates glucose-6-phosphatase.• Yet, glucose suppresses the NET production of glucose from the liver.• Effect on 6PFK2• Glucose induces/maintains the dephosphorylation of 6PFK2• increased Frutose-2,6-bisphosphate leads to decreased GNG— via inhibiting FBPase• F-2,6-P2 Regulates Glucose Homeostasis • Nutrients and hormones regulate glucose homeostasis via 6PFK2/FBP2 and hepaticF-2,6-P2 levels. Regulation of GNG: Role of Insulin• Insulin is the most powerful hormone that suppresses gluconeogenesis.• Effect on PEPCK• Insulin suppresses PEPCK expression• Effect on 6PFK2• Insulin brings about an increase in fructose-2,6-bisphosphate, whichin turn inhibits FBPase.• Effect on glucose-6-phosphatase• Insulin suppresses glucose-6-phosphatase expression.• Regulation of GNG: Role of Glucagon• Glucagon is a powerful hormone that stimulates gluconeogenesis.• Effect on PEPCK• Glucagon stimulates PEPCK gene expression• increase of PEPCK activity leads to increased Gluconeogenesis• Effect on 6PFK2• Glucagon induces phosphorylation of 6PFK2• decreased Frutose-2,6-bisphosphate leads to increased GNG— via releasing the inhibitory effect on FBPase• Decrease of GNG• when glucose levels are high:• glucose and insulin are high, so decreased glucagon• decrease in PEPCK, FBPase, G6Pase• Increase of GNG• when glucose levels are low:• decrease glucose and insulin, increased glucagon• thus increase of PEPCK, FBPase, G6Pase• Integrative Regulation of Glucose Homeostasis• Under a given nutritional condition, such as feeding, multiple tissues/organs are involved in the regulation of glucose homeostasis .• Glucose production from liver is reduced• Glucose