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76 SECTION II BIOCHEmISTRY ``BIOCHEMISTRY—METABOlISM BIOCHEmISTRY ``BIOCHEMISTRY—METABOlISM
Glycolysis regulation, Net glycolysis (cytoplasm):
+
+
key enzymes Glucose + 2 P i + 2 ADP + 2 NAD 2 pyruvate + 2 ATP + 2 NADH + 2 H + 2 H 2 O.
Equation not balanced chemically, and exact balanced equation depends on ionization state of
reactants and products.
REqUIRE ATP Glucose Glucose-6-P Glucose-6-P ⊝ hexokinase.
Hexokinase/glucokinase
Fructose-6-P ⊝ glucokinase.
Fructose-6-P Fructose-1,6-BP AMP ⊕, fructose-2,6-bisphosphate ⊕.
Phosphofructokinase-1
(rate-limiting step) ATP ⊝, citrate ⊝.
PRODUCE ATP 1,3-BPG 3-PG
Phosphoglycerate kinase
Phosphoenolpyruvate Pyruvate Fructose-1,6-bisphosphate ⊕.
Pyruvate kinase
ATP ⊝, alanine ⊝.
Regulation by Fructose bisphosphatase-2 (FBPase-2) and phosphofructokinase-2 (PFK-2) are the same
fructose-2,6- bifunctional enzyme whose function is reversed by phosphorylation by protein kinase A.
bisphosphate FBPase-1
Gluconeogenesis Fructose-6-P Fructose-1,6-BP Glycolysis
PFK-1
FBPase-2 PFK-2
(active in (active in
fasting state) fed state)
Fructose-2,6-BP
Fasting state: glucagon cAMP protein FaBian the Peasant (FBP) has to work hard
kinase A FBPase-2, PFK-2, less when starving.
glycolysis, more gluconeogenesis.
Fed state: insulin cAMP protein Prince FredericK (PFK) works only when fed.
kinase A FBPase-2, PFK-2, more
glycolysis, less gluconeogenesis.
Pyruvate Mitochondrial enzyme complex linking The complex is similar to the α-ketoglutarate
dehydrogenase glycolysis and TCA cycle. Differentially dehydrogenase complex (same cofactors,
complex regulated in fed (active)/fasting (inactive) states. similar substrate and action), which converts
+
Reaction: pyruvate + NAD + CoA acetyl- α-ketoglutarate succinyl-CoA (TCA cycle).
CoA + CO 2 + NADH.
Contains 3 enzymes requiring 5 cofactors:
1. Thiamine pyrophosphate (B 1 )
2. Lipoic acid
3. CoA (B 5 , pantothenic acid) The Lovely Coenzymes For Nerds.
4. FAD (B 2 , riboflavin) Arsenic inhibits lipoic acid. Arsenic poisoning
+
5. NAD (B 3 , niacin) clinical findings: imagine a vampire (pigmentary
+
Activated by: NAD /NADH ratio, ADP skin changes, skin cancer), vomiting and having
2+
Ca . diarrhea, running away from a cutie (QT
prolongation) with garlic breath.
FAS1_2019_01-Biochem.indd 76 11/7/19 3:16 PM
