BIOL 541 1st Edition Lecture 18 Outline of Last Lecture I. Glycogenesis and glycogenolysis Outline of Current Lecture II.RegulationIII. Lipid catabolismIV. CalculationsCurrent LectureBiochem Lecture 18- Regulation of glycogenolysis:Strategy:Glycogen storage is a form of energy. Excess of energy would favor shuttling into glycogen- no need to breakdown glycogen breakdown. Glycogen synthase favored by increase in levels of ATP and excess of acetyly COA or Glucose 6 phosphate. Glycogenolysis occurs when energy levels are low, ADP levels are high, AMP levels are high, or NAD levels are high and is favored by Ca in muscles and liver, as hormones level increase Ca levels in liver.Glycogen is converted to glucose by glycogen synthase from UDP- glucose to the chain and UDP left behind.Glycogen phosphorylase where phosphate group leaves and glucose 1 phosphate made. Regulation of enzyme by phosphorylation and is done by dedicated kinase such as pyruvate dehydrogenase phosphorylase “phosphorylase kinase” which consists of 16 subunits. 4 copies each of alpha, beta, delta and gamma. Gamma subunit is the catalytic site. Gamma peptide camoldulin and alpha and beta regulatory subunits themselves are phosphorylated.Regulatory cascade: Alpha beta phosphorylates and activates phosphatase kinase. Fasting has low energy and stimulates break down of glycogen. The major regulatory hormone is glucagon (in liver) and epinephrine (in muscles). Both use cAMP as a secondary messenger and activates protein kinase A. Protein kinase A These 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.phosphorylates glycogen synthase. Series of arrows for incremental reactions. Number of kinases used and inhibit slightly at each level, rheostat for degrees of phosphorylation. AMP kinase is active when AMP levels increase when energy level is low, and thus lead to decreasing activity of glycogen synthase. Glycogen synthase is allosterically inhibited by low energy level, increase in ADP level and increase in level of Pi, and is stimulated by increasing level of substrate. This is a feed forward reaction.Levels are regulated as well:1. Lysozyme- In the stomach are hydrolytic enzymes that fuse with endosomes.2. Proteosomes- Endogenous protein, non membrane bounded tubular structures. Walls of the tube formed by proteases where 1 side protein goes in and 2 side amino acids come out.Identifying the protein is done by labeling which is done by 76 amino acids called ubiquitin (everywhere protein). Ubiquitin is attached to target protein via iso peptide bond (branched peptide formed).Ubiquitin molecular condensation:Process of ubiquitin needs 3 enzymes: E1, E2, and E3. E1 and E2 are common to other systems. E3 ligase provides specificity and chooses the protein to be ubiquinated.Malin E3 ligase targets glycogen synthase. Problem is that it can not find glycogen synthase and needs localizing subunit formed by laforin (glycogen peptidase and remove trace amounts of phosphate). Phosphorylated and binds to malin and bump it to glycogen synthase, thereby glycogen binding site is localized. AMP kinase phosphorylates laforin when energy levels are high. Glycogen particle, malin, E3 ubiquinates glycogen synthase and target proteosome where physical destruction occurs. Actual glycogen broken down. Protein kinase A phosphorylates kinase alpha and beta subunits and activates phosphorylase kinase and phosphatase phosphorylates (tetramer- active form) but exits as a dimer. Dimer is phosphorylase B which has strict allosteric regulation where increase in energy stimulates it anddecrease in levels of glucose 6 phosphate inhibits it. It is less active due to allosteric regulation. Phosphatase A which is a tetramer and fully active form has no allosteric regulation. Fine tuning is done by acetylation where increasing levels of acetyl COA, and increasing levels of phosphatase causes removal of phosphate group. When energy is low, NAD level is high, deacetylase is activated to remove acetate prolonging phosphatase step thus favoring glycogen break down.Delta subunit is the Ca binding protein called calmodulin which is a Ca sensor. Increasing levels of Ca binds to calmodulin and stimulates phosphorylase kinase. Proponin, a muscle protein, activates it even when not phosphorylated. Phosphatase PP1 (protein phosphate 1) takes phosphate group from glycogen synthase, glycogen phosphatase and phosphorylase kinase and inactivates them. So protein kinase A phosphorylates and activates the inhibition of the phosphorylated stage, phosphorylase kinase making it inactive. When enrgy levels are low and increasing levels of AMP, phosphorylation of laforinbind malin, glycogen E3 ligase, and ubiquinate and phosphorylate and destroy. Glycogen synthase increase and protein phosphatase 1 also regulated.Lipid metabolism: Lipid catabolism:Lipids are stored as triglycerides- 3 fatty acids as ester of glycerol.1. Digestion by lipase: Rate limiting step in fatty acid catabolism. Not a single lipase but 3 lipases that work in sequence.a. Adipose triacyl glycerol lipase removes 1 fatty acid from triglycerides leaving behind diglyceride and 1 free fatty acid. This is regulated by induction where increasing levels of glucocorticoids during fasting induce gene for adipose triglyceride lipase. In addition, protein kinase A can facilitate hydrolysis of phosphorylase A protein. Lipids are found as droplets in cells. The droplet of lipid is surrounded by protein membrane called as perilipins (perimeter of lipid droplet) whichis the target of protein kinase A (2nd messenger for epinephrine)- lipolysis of fat tissue and attracted by phosphatase co activator of adipose triglyceride lipase is CGI58. Diglyceride is acted upon by hormone sensitive lipase (HSL) forming monoglyceride and 2nd free fatty acid. This is directly phosphorylated and activated by protein kinase A. Finally, monoglyceride lipase removeslast fatty acid and gives glycerol and 3rd fatty acid. This is not regulated and present in high levels and constitutively activated as substrate is required and indirect regulation as monoglycerides are needed.b. 2nd step is activation of fatty acid:This is the attachment of fatty acid to co enzyme A. Carboxylic acid attached to phosphate group or sulphur is a high energy bond. Energy is expended to do this : 2 energy bonds ( 2 ATP)