Chapter 15 Principles of Metabolic Regulation: Glucose and Glycogen Part 1 Principles of Metabolic Regulation Key topics: Learning Goals – Principles of regulation in biological systems – Glycolysis vs. gluconeogenesis? How are they regulated? Metabolic Pathways • The biochemical reactions in the living cell―metabolism―are organized into metabolic pathways • The pathways have dedicated purposes: – Extraction of energy – Storage of fuels – Synthesis of important building blocks – Elimination of waste materials • The pathways can be represented as a map – – – – Follow the fate of metabolites and building blocks Identify enzymes that act on these metabolites Identify points and agents of regulation Identify sources of metabolic diseases All Sorts of Things Affect Enzyme Activity Proteins Can be Covalently Modified Metabolome of Escherichia coli growing on Glucose Take Me Back to Chapter 6 Km vs. [Metabolite] Pathway’s Flux is Controlled at Select Points Which reaction is driving this sequence? Which has the most negative ΔG ? Elastisity Coefficient Depends on [S] Energy Charge: 0.90 0.82 Role of AMP-activated Protein Kinase Metabolic Regulation Functions To: 1. Maximize efficiency of energy source use, stops futile cycles. 2. Partitions metabolites and enzymes (alternative pathways – Glycolysis and PPP). 3. Use best suited energy source of the immediate need of the organism (glucose, glycogen, fatty acids, amino acids). 4. Shuts down biosynthesis when products accumulate. What is a Futile Cycle? Have we seen one already? Which Enzyme Controls Glycolytic Flux ? Experiment: purified enzymes added to liver cell extract carrying out glycolysis with own enzymes. Flux Coefficients Determine Flow Path Insulin Regulation On Muscle Cells EOC Problem 5 is all about cytoplasmic concentration of glucose Hexokinase-1 Regulation in Muscles Glucose-6-Phosphate is a negative allosteric regulator of Hexokinase I and II So how many binding sites on Hexokinase I and II for Glucose-6-P are there? Glucose + ATP Glucose-6-P + ADP Potential Futile Cycles between Glycolysis and Gluconeogenesis Hexokinase Isozymes Hexokinase IV Regulation in Liver Glycogen Glucokinase=Hexokinase IV Signal Sequences: 300-310 ELVRLVLLKLV says export me to the cytoplasm. 347-358 QIHNILSTGLR says associate with GKRP: Glucokinase Regulatory Protein = GKRP Nuclear Localization Sequence: PKKKRKV (prototype) + Importins α and β Fig 27-42 pgs 1104-1105 NLS = Nuclear Localization Sequence. 4-8 aa’s of which there are consequitive K’s and R’s. PFK-1 Is Energy Regulated Three Major forms of Allosteric Regulation of PFK-1 EOC Problem 4 is all about PFK-1 regulation Adenylates and Citrate on PFK-1 and FBPase-1 This Sugar was not discovered until the ‘80s At pH = 7…what is the Charge? F2,6BP is a Major Regulator F-2,6-BP is a Major Regulator Reciprocal Effects Making and Breaking F2,6BP This is super easy to remember: PFK-1 phosphorylates the number 1 carbon of F6P, PFK-2 phosphorylates the number 2 carbon of F6P WOW !!! PFK-2 and FBP-2 are the Same Protein Phosphoprotein Phosphatase is Stimulated by Xylulose-5-P stimulated Pyr Kinase Xylulose-5-P also stimulates fatty acid synthesis Phosophoprotein Phosphatase can Recognize Different Proteins EOC Problem 3 is about Oxygen supply and this Regulation Things to Know and Do Before Class 1. Regulation of enzyme activity: allosteric, covalent modification, “hiding” out in another cell compartment. 2. Concept of enzyme elasticity. 3. Role of the adenylates in control, and AMPKinase. 4. Fructose-2,6-bisphosphate: how it is made and broken and how it helps prevent a futile cycle. 5. Isozymes (hexokinase). There are others. 6. Pyruvate kinase allosteric and covalent modification (liver only). 7. EOC Problems: 3, 4, 5.