Principles of Metabolic Regulation:Glucose and Glycogen

Part 1

Chapter 15

Principles of Metabolic Regulation

– Principles of regulation in biological systems

– Glycolysis vs. gluconeogenesis? How are they regulated?

Key topics: Learning Goals

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]

Which reaction is driving this sequence? Which has the most negative ΔG ?

Pathway’s Flux is Controlled at Select Points

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

This is super easy to remember: PFK-1 phosphorylates the number 1 carbon of F6P,PFK-2 phosphorylates the number 2 carbon of F6P

Making and Breaking F2,6BP

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.