Lecture 7 - Glycolysis Flashcards
What inhibits hexokinase?
G-6-P
What enzyme controls the entry of G6P into the glycolysis pathway?
PFK-1
What inhibits PFK1? Activates?
Allosteric inhibition: ATP
Allosteric activation: AMP
What are the relative Km values of hexokinase and glucokinase? Where is each found?
Hexokinase lower Km than Glucokinase. RBCs need glucose! Glucokinase - liver, Hexokinase - most everywhere else
List the glycolysis substrates in order.
Glucose > G6P > F6P > F1,6B > G3P > 1,3BPG > 3PG > 2PG > PEP > P
Where does glycolysis occur?
Cytoplasm
Source of ATP for blood cells?
Anaerobic glycolysis. They have no mitochondria!
List the glycolysis enzymes in order.
Hexokinase, PHI, PFK1, Aldolase, Triose phosphate isomerase, Glyceraldehyde 3-phosphate dehydrogenase, Phosphoglycerate kinase, Phosphoglycerate mutase, Enolase, Pyruvate kinase
(H-PHI-PFK1-A-TPI-G3PDH-PGK-PGM-E-PK)
What is the primary fuel used the the heart under normal conditions?
Fatty acids: 60-80%
Note: Glucose is 20-30%, only 2% of total ATP used from glycolysis! This is significant for ischemia since
What are the glucose transporters in the heart? What is significant about the dominant class of glucose transporters in the heart?
GLUT1 (10%) and GLUT4 (90%). GLUT4 is insulin dependent.
What enzymes are directly involved in generating substrates for the Lactate dehydrogenase?
G3P Dehydrogenate (produces NADH) and pyruvate kinase (produces pyruvate)
G6P can enter other pathways besides glycolysis. List these.
Glycogen, pentose phosphate, blood glucose (liver)
What two groups of cells rely solely on anaerobic glycolysis?
RBCs and lens cells (eye)
What enzyme allows G6P to be released from the cell? Where is this enzyme found?
G6P phosphatase, found in liver and renal cortex
What type of glucose transporter is found in the liver?
GLUT2 (constitutively active - not insulin regulated)
What step in glycolysis is heavily regulated and irreversible (a committed step)?
Conversion of F6P to F1,6B by PFK1
Where does arsenate inhibit ATP production? How does it inhibit?
Substitutes for Pi in rxns. 2nd PO4 at the G3P DH step.
What 2 steps in glycolysis are not reversible?
F1,6BP, Pyruvate kinase
Explain the types of lactic acidosis.
Type A: Occurs when there is evidence of poor oxygen perfusions
Type B: No evidence ox depletion, liver dysfunction, ox phos uncoupling
Define lactic acidosis.
acidosis - persistant high lactate levels > 5mM in presence of low pH
How do cytosolic NADH electrons enter the mitochondrial matrix (pathway common in all tissues)?
G3P phosphate shuttle (present in all tissues)
What is the ATP/NADH ratio through the G3P shuttle?
1.5ATP/NADH
How do cytosolic NADH electrons enter the mitochondrial matrix (pathway present in heart, liver, kidney)
Malate-aspartate shuttle
What is the ATP/NADH ratio for the malate-aspartate shuttle?
2.5ATP/NADH
What specific interaction allow the malate-aspartate system to “drop off” its electrons in the mitochondrial matrix?
Malate + NAD(+) => Oxaloacetate + HADH
(Malate is oxidized, NADH goes to ETC)
(See page 402 in Mark’s)
What enzyme is responsible for converting oxaloacetate to aspartate within the context of the Malate-aspartate shuttle?
alpha-keto-glutarate
List the key regulated steps in glycolysis.
1) Hexokinase (glucokinase in liver)
2) PFK1
3) Pyruvate kinase
4) Pyruvate dehydrogenase
What regulates Hexokinase function?
Inhibited by presence of G6P
What regulates Glucokinase function?
Induced by insulin
What regulates PFK1
Induction: AMP, fructose-2,6bisP
Inhibition: ATP, acidosis, citrate
What regulates pyruvate kinase?
+ fructose-1,6-bisP
- ATP
- cAMP dependent kinase (glucagon in liver)
What regulates pyruvate dehydrogenase?
- NADH
- Acetyl CoA
+ ADP
Explain the function of GKRP.
Translocates glucokinase between the cytoplasm and the nucleus (in nucleus GK is inactive, cytoplasm its active).
Explain the regulation of GKRP.
- Fructose-6-P inhibits GKRP by aiding it in binding GK
- Glucose & fructose-1-P block GKRP-GK interactions activating GK
What is the effect of insulin on glucokinase?
Increases number of GK units
What is the effect of G6P on glucokinase?
Not a lot. Liver needs to be able to synthesize glycogen even when blood glucose is elevated.
What is the role of PFK-2?
Deal functions:
1) KINASE: Phosphorylates F6P to F2,6BP
2) PHOSPHATATSE: F2,6BP to F6P
What is the significance of F2,6BP?
- Most potent activator of PFK-1
- Most potent inhibitor of fructose-1,6-bisphosphatase (gluconeogenesis in liver)
What is the effect of PFK2 phosphorylation in the heart?
Kinase activity activated > F2,6BP increased > glycolysis
What is the effect of PFK2 phosphorylation in the liver?
Kinase activity inhibited > F2,6BP decreased > Gluconeogenesis can occur
Pyruvate dehydrogenase function
Oxidizes pyruvate following glycolysis > Acetyl-CoA for TCA
Dichloroacetate
Inhibits PDH kinase, activated PDH
Effect of increased PDH activity
Increased Acetyl-CoA into TCA. Heart uses more glucose.
