1. Regulation of Phosphofructokinase-1: Too Much of a Good Theme?
Eric Niederhoffer
SIU-SOM

2. Curriculum Context
Problem-based learning using electronic patient cases
Organ-system, integrated disciplines
Specific example - diabetes mellitus/alcoholic ketoacidosis
Learning Issues
Which steps in metabolic pathways are regulated by insulin, glucagon, or other important hormones or metabolites?
How do insulin and glucagon balance the degradation, synthesis, and storage of glucose?
How does the regulation of glycolysis compare between liver, cardiac muscle and skeletal muscle?

3. Glycolysis: Regulatory Steps
Glucagon
Liver
Liver
Insulin
Glc
Acetyl-CoA
Pyr
F6P
F16BP
PEP
G6P
Adipose
Liver
Heart GK Ep HK
Heart
Liver
F26BPase
PFK-2
PFK-1 PK
PDH
Glc: glucose G6P: glucose-6-phosphate F6P: fructose-6-phosphate F16BP: fructose-1,6-bisphosphate PEP: phosphoenolpyruvate Pyr: pyruvate
PDH: pyruvate dehydrogenase GK: glucokinase HK: hexokinase
PFK: phosphofructokinase F26BPase: fructose-2,6-bisphosphatase
PK: pyruvate kinase PDH: pyruvate dehdrogenase Ep: epinephrine

4. Regulation Focus Glc G6P ATP Citrate PEP H+ F6P PFK-2 PFK-1 F26BP
NH4+
AMP Pi
Pi: inorganic phosphate Glc: glucose F6P: fructose-6-phosphate
G6P: glucose-6-phosphate ATP: adenosine triphosphate PFK: phosphofructokinase
F16BP: fructose-1,6-bisphosphate F26BP: fructose-2,6-bisphosphate
PEP: phosphoenolpyruvate 2ADP to ATP + AMP by adenylate kinase

5. PFK-1 - Facts Two genes - PFKL (21q), PFKM (12q)
Tetramer - muscle (M4), liver/kidney (L4), platelet (M4, M3L, M2L2, ML3, L4)
T and R states
Activators - AMP, ADP, cAMP, Pi, F6P, F16BP, F26BP, NH4+
Inhibitors - ATP, citrate, PEP, H+
Interaction with renal H+ ATPase
Glycogen storage disease VII (Tauri) - autosomal recessive, gout, increased O2 affinity (decreased 23BPG)

6. PFK-2 - Facts
Four genes - PFKFB1 (X), PFKFB2 (1), PFKFB3 (10), PFKFB4 (3)
PFK-2 dimer
Bifunctional protein (PFK/F26BPase)
Activators/inhibitors - similar to PFK-1 except no ATP inhibition
Brain no (or low) mRNA detected
Skeletal muscle - F6P regulates
Phosphorylation - liver (Ser32, N term), cardiac (Ser406[466,483],Thr475, F26BPase)

7. F26BPase-PFK-2 Regulation Comparison
F26BPase-PFK-2P
Insulin
PrPase2A
Glucagon Ep
PKA
Liver
F26BPase-PFK-2
F6P↑
F6P↓
Skeletal Muscle
F26BPaseP-PFK-2
F26BPase-PFK-2
???
PKA Ep
Insulin
AMPK/AKT/WISK
Heart
Activated Inhibited F6P: fructose-6-phosphate
PFK: phosphofructokinase F26BPase: fructose-2,6-bisphosphatase Ep: epinephrine
PKA: protein kinase A ???: protein phosphatase possibly PrPase: protein phosphatase
Glucagon decreases transcription of PFK-1 AMPK: AMP kinase
WISK: wortmannin-sensitive and insulin-stimulated protein kinase