Metabolic Enzymes

Question 0

Transketolase
Function?
Regulation
Substrates/Products?

Answer 0

Function: Transfers 2 carbons at a time during Pentose Pathway
Regulation: TPP cofactor

Question 1

Glucos-6-Phosphate Dehydrogenase
Function?
Regulation
Substrates/Products?

Answer 1

Function: First oxidative/irreversible step in pentose pathway
Inhibited by: NADPH
Substrates/Products: G6P -> 6 Phosphogluconate

Question 2

Pyruvate Dehydrogenase
Function?
Regulation
Substrates/Products?

Answer 2

Function: Convert Pyruvate to Acetyl CoA for TCA
Regulation: Inhibited by NADH/A-CoA; deactivated when phosphorylated by kinase which is in turn, inhibited by low ATP
Cofactors: CoA, TPP, Lipolic Acid, FAD, NAD+
Substrates/Products: Pyruvate + CoA -> CO2 + NADH + Acetyl CoA

Question 3

Pyruvate Carboxylase
Function?
Regulation
Substrates/Products?

Answer 3

Function: Irreversible conversion of pyruvate to oxaloacetate as part of gluconeogenesis
Regulation: stimulated by high Acetyl CoA; Uses Biotin
Substrates/Products: Pyruate + 2ATP -> Oxaloacetate

Question 4

Lactate Dehydrogenase
Function?
Regulation?
Substrates/Products?

Answer 4

Function: Regenerates oxidized NAD+ for use in glycolysis
Regulation: Occurs in absence of O2
Substrates/Products: Pyruvate + NADH -> NAD+ + Lactate

Question 5

Citrate Synthase
Function?
Regulation?
Substrates/Products?

Answer 5

Function: First step in TCA
Regulation: Inhibited by citrate
Substrates/Products: Acetyl CoA + Oxaloacetate -> CoASH + Citrate

Question 6

Isocitrate Dehydrogenase
Function?
Regulation?
Substrates/Products?

Answer 6

Function: irreversible step in TCA; oxidative decarboxylation reaction
Regulation: Stimulated by ADP/Ca++, Inhibited by NADH/ATP
Cofactors: CoA, TPP, Lipolic Acid, FAD, NAD+
Substrates/Products: Isocitrate + NAD+ -> NADH + CO2 + alpha-ketoglutarate

Question 7

Alpha-ketoglutarate Dehydrogenase
Function?
Regulation?
Substrates/Products?

Answer 7

Function: oxidative decarboxylation reaction to form NADH in TCA
Regulation: Stimulated by Ca++, Inhibited by NADH/Succinyl CoA
Substrates/Products: Alpha-ketoglutarate + CoASH + NAD+ -> CO2 + NADH + Succinyl CoA

Question 8

Succinyl CoA Synthetase / Succinate Thiokinase
Function?
Regulation?
Substrates/Products?

Answer 8

Function: 3rd substrate level phosphorylation in gluc metabolism (1st in TCA); formation of GTP
Regulation:
Substrates/Products: Succinyl CoA + GDP -> CoASH + GTP + Succinate

Question 9

Succinate Dehydrogenase
Function?
Regulation?
Substrates/Products?

Answer 9

Function: TCA- oxidation of FAD; also Complex II of e- transport chain (where FAD2H enters)
Regulation:
Substrates/Products: Succinate + FAD -> Fumarate + FAD2H

Question 10

Malate Dehydrogenase
Function?
Regulation?
Substrates/Products?

Answer 10

Function: recreation of oxaloacetate in TCA and last oxidation step of TCA
Regulation:
Substrates/Products: Malate + NAD+ -> NADH + Oxaloacetate

Question 11

NADH Dehydrogenase
Function?
Regulation?
Substrates/Products?

Answer 11

Function: Complex I of ETC, where NADH enters ETC
Regulation
Substrates/Products

Question 12

Ubiquinone Cytochrome-C Oxidoreductase
Function?
Regulation?
Substrates/Products?

Answer 12

Function: Complex III of ETC

Question 13

Cytochrome oxidase
Function?
Regulation?
Substrates/Products?

Answer 13

Function: Complex IV of ETC

Question 14

Fructokinase
Function?
Regulation?
Substrates/Products?

Answer 14

Function: Convert fructose to Fructose -1-P (using ATP) in Liver to use fructose in glycolysis (in lieu of glucose). Problematic in Essential Fructosuria
Regulation:
Substrates/Products: Fructose + ATP -> ADP Fructose-1-P

Question 15

Aldolase B
Function?
Regulation?
Substrates/Products?

Answer 15

Function: Converts Fruc-1-P to 3 carbon glycolytic substrates; problematic in Hereditary Fructose Intolerance (severe)
Regulation:
Substrates/Products: Fructose-1-P -> Glyceraldehyde OR dihydroxyacetone

Question 16

Galactokinase
Function?
Regulation?
Substrates/Products?

Answer 16

Function: Convert galactose to galactose 1-P for eventual use in glycolysis
Regulation:
Substrates/Products: Galactose + ATP -> ADP + galactose-1-P

Question 17

Galactose-1-P Uridylyltransferase
Function?
Regulation?
Substrates/Products?

Answer 17

Function: Convert galactose-1-P to glucose-1-P (with UDP attached intermediate). Problematic in Galactosemia (back up of gal-1-P so inorganic phosphate is tied up)
Regulation:
Substrates/Products: Gal-1-P -> UDP-gal -> UDP-glu -> Glu-1-P

Question 18

Sorbitol Dehydrogenase
Function?
Regulation?
Substrates/Products?

Answer 18

Function: Converts Sorbitol to Fructose in Liver. Absent in Lens/Nerve/Kidney so that when blood glucose is very high, sorbitol is created but not removed from cell = tissue swelling
Regulation: Only active in high glucose concentration
Substrates/Products: Sorbitol + NAD+ -> NADH + Fructose

Question 19

Debrancher Enzyme
Function?
Regulation?
Substrates/Products?

Answer 19

Function: Moves last 3 residues at 1,6 bond to another branch (because phosphorylase is sterically hindered)
Regulation:
Substrates/Products: Glycogen -> Glucose (small amount)

Question 20

Glycogen Phosphorylase
Function?
Regulation?
Substrates/Products?

Answer 20

Function: Phsophorylytic cleavage creating phosphorylated glucose product that can’t leave cell (quick reuse for glycolysis). Cleaves at 1,4 bond.
Regulation: Phosphorylated by Glyc Phos Kinase = activated. Low Blood Gluc = High cAMP = Glyc Phos is active. Activated by Ca++ and AMP, Inhibited by ATP/Glucose
Substrates/Products: Glycogen -> Glucose-1-P

Question 21

Phosphoglucomutase
Function?
Regulation?
Substrates/Products?

Answer 21

Function: Interconvert Glu-1-P and Glu-6-P
Regulation
Substrates/Products: Glu-1-P Glu-6-P

Question 22

Glucose-6-Phosphatase
Function?
Regulation?
Substrates/Products?

Answer 22

Function: Convert Glucose-6-P to Glucose (opposite function of Hexokinase). Used in Glycogen degradation and Gluconeogenesis

Question 23

UDP-glucose-pyrophosphorylase
Function?
Regulation?
Substrates/Products?

Answer 23

Function: Convert Glucose-1-P to UDP-glucose (which can go to form glycogen or can be converted to galactose)
Regulation:
Substrates/Products: Glu-1-P + UTP -> UDP-glucose

Question 24

Branching Enzyme Function? Regulation? Substrates/Products?

Answer 24

Function: AKA 4:6 Transferase. AKA Glycogen Synthase Regulation: Inhibited by Ca++, phosphorylated by PKA (high cAMP) = deactivated. Substrates/Products: Glycogen primer (glycogenin) + UDP-Glu -> glycogen

Question 25

Phosphoenolpyruvate Carboxylase Function? Regulation? Substrates/Products?

Answer 25

Function: Convert oxaloacetate to Phosphoenolpyruvate in gluconeogenesis. Occurs in mitochondria in anaerobic and in cytosol in aerobic. Regulation: Increased by Glucagon/Epinephrine, Decreased by Insulin Substrates/Products: Oxaloacetate + 2GTP -> PEP

Question 26

Fructose-1,6-Biphosphatase Function? Regulation? Substrates/Products?

Answer 26

Function: Convert F-1,6-BP to F-6-P in Gluconeogenesis Regulation: Inhibited by F26P/AMP; Increased by fasting. Glucagon (Liver) = increase cAMP/PKA = PFK2-P inactive = FBP1 active Epinephrine (Muscle) = increases cAMP= PFK2-P active = FBP1 inactive Substrates/Products: F-1,6-BP -> F-6-P

Question 27

Hexokinase Function? Regulation? Substrates/Products?

Answer 27

Function: First step in Glycolysis. Irreversible (phosphorylated glucose can't leave cell). Deficiency in hexokinase in RBC can lead to anemia (RBC can't get ATP). Regulation: Feedback inhibition Substrates/Products: Glucose + ATP -> ADP + Glucose-6-P

Question 28

Phosphofructokinase 1 Function? Regulation? Substrates/Products?

Answer 28

Function: Rate-limiting step of Glycolysis (Irreversible). Regulation: regulated by F-2,6-BP. High glucose = cAMP deactive = PFK 2 active = high F-2,6-BP. Substrates/Products: F-6-P + ATP -> ADP + F-1,6-BP

Question 29

Phosphofructokinase 2 Function? Regulation? Substrates/Products?

Answer 29

Function: Regulator of glycolysis through PFK1. Under cAMP/AC/hormone regulation Regulation: cAMP activates PKA which phosphorylates PFK2 = deactivated (no glycolysis). Insulin/high glucose deactivate cAMP Substrates/Products: F-6-P -> F-2,6-BP

Question 30

Glyceraldehyde-3-P Dehydrogenase Function? Regulation? Substrates/Products?

Answer 30

Function: Oxidation step creating NADH reducing agent in Glycolysis Regulation: Substrates/Products: Glyc-3-P + NAD+ -> NADH + 1,3-BPG (through mutase can be changed to 2,3 BPG used in hemoglobin)

Question 31

Phosphoglycerate Kinase Function? Regulation? Substrates/Products?

Answer 31

Function: First Substrate Level Phosphorylation of Glycolysis. (creates ATP directly from enzymatic reaction) Regulation: Substrates/Products: 1,3-BPG + ADP -> ATP + 3-Phosphoglycerate

Question 32

Enolase Function? Regulation? Substrates/Products?

Answer 32

Function: Highest free energy released as result of hydrolysis Regulation: Substrates/Products: 2 Phosphoglycerate -> H2O + PEP

Question 33

Pyruvate Kinase Function? Regulation? Substrates/Products?

Answer 33

Function: Last step (Irreversible) of Glycolysis. Another Substrate level phosphorylation; Deficiency causes 2,3BPG to increase from backflow Regulation: Occurs in liver; Inhibited by phosphorylation, high Alanine (similar to pyruvate= competitive inhibitor) Substrates/Products?