Metabolism Major Enzymes

Question 1

Hexokinase

Answer 1

• Used in glycolysis(step 1)
• Phosphorylates glucose into glucose-6-phosphate
• Uses ATP
• Traps glucose in cell(GLUT cannot bind G6P)
• G6P can be used in glycolysis to make energy or stored for later(glycogen)

Question 2

Phosphofructokinase(PFK-1)

Answer 2

• Used in glycolysis(step 3)
• 2nd ATP requiring step
• Transfers phosphate from ATP to C1 hydroxyl of Fructose-6-phosphate -> makes Fructose 1,6 bisphosphate
• Activated by AMP, ADP, or Fructose 2,6-bisphosphate
• Inhibited by ATP

Question 3

Pyruvate Kinase

Answer 3

• Used in glycolysis(step 10)
• Releases ATP
• Uses phosphenolpyruvate(PEP) to form pyruvate
• Inhibited by phosphorylation and other allosteric regulators
• In low glucose levels: glucagon/epinephrine/cortisol uses protein kinase to phosphorylate -> inactive
• In high glucose levels: insulin use phosphatase to dephosphorylate -> active
• Activated by AMP, F1,6BP
• Inhibited by ATP, Alanine, Acetyl-CoA

Question 4

Phosphoglucomutase

Answer 4

• Used in glycogen synthesis
• Glucose still phosphorylated to make G6P -> G6P isomerized to form Glucose-1-phosphate
• In glycogenolysis: converts glucose-1-phosphate back to glucose-6-phosphate

Question 5

UDP-glucose pyrophosphorylase

Answer 5

• Used in glycogen synthesis
• Uses UTP to activate glucose-1-phosphate to make UDP-glucose

Question 6

Glycogen Synthase

Answer 6

• Used in glycogen synthesis
• Uses UDP-glucose to create alpha(1,4) glycosidic bonds on non-reducing ends of glycogen

Question 7

Glycogen Phosphorylase

Answer 7

• Used in glycogenolysis
• Activated with glucagon and epinephrine signaling
• Uses Pi to release glucose-1-phosphate from non-reducing ends
• Inhibited by ATP and glucose-6-phosphate
• Stimulated by AMP

Question 8

PDC Enzymes

Answer 8

• E1: Decarboxylates pyruvate
• E2: Transfers acetyl
• E3: Dehydrogenase to convert FADH to FAD
• Acetyl CoA inhibits E2
• NADH inhibits E3

Question 9

Succinate Dehydrogenase

Answer 9

• Used in TCA and ETC
• Forms fumarate from succinate in TCA cycle
• Complex 2 in ETC. Where FADH comes in

Question 10

Regulated enzymes in TCA

Answer 10

• Reactions that are favorable(negative delta G)
• Citrate synthase(Step 1): Uses acetyl-coA and oxaloacetate to make citrate. Inhibited by citrate
• Isocitrate dehydrogenase(Step 3): Uses isocitrate to form alpha-ketoglutarate. Inhibited by NADH. Stimulated by ADP and Ca2+. Releases CO2 and NADH
• Alpha-ketoglutarate dehydrogenase(Step 4): Uses alpha-ketoglutarate to form Succinyl-CoA. Releases NADH and CO2. Inhibited by NADH. Stimulated by Ca2+

Question 11

Enzymes used in ETC

Answer 11

• NADH-Q Oxidoreductase: Complex 1
• Succinate-Q reductase: Complex 2
• Q-cytochrome c oxidoreductase: Complex 3
• Cytochrome c oxidase: Complex 4

Question 12

ATP Synthase

Answer 12

• F1 carries out catalytic synthesis of ATP in matrix
• F0 is integral membrane protein and anchors complex to membrane
  - Binding of H causes rotation in ring of c subunits in F0
  - Rotation of ring rotates, rotates gamma subunit including a conformational change in the beta subunit. H+ released into the matrix
  - Conformational changes in the F1 beta-subunits are responsible for ATP synthesis

Question 13

Triacylglycerol Lipase

Answer 13

• Hydrolyze ester bonds to produce free fatty acids and glycerol
• Activated by phosphorylation from PKA
• Also known as hormone-sensitive lipase

Question 14

Acyl CoA Synthetase

Answer 14

• Catalyzes reversible reaction using ATP to form fatty acyl CoA
• Pyrophosphate hydrolysis to 2 Pi drives reaction in forward direction

Question 15

Carnitine Shuttle

Answer 15

• Used to move acyl-CoA into matrix for beta-oxidation
• Carnitine Acyltransferase 1: Moves acyl chain onto carnitine from CoA
• Carnitine Acyltransferase 2: Moves acyl chain back onto CoA

Question 16

4 Steps of Beta Oxidation

Answer 16

• Acyl CoA dehydrogenase: produces FADH2 and creates double bond in fatty acid chain
• Hydratase: adds water across double bond
• Dehydrogenase: produces NADH and creates a keto group on the beta-carbon in the chain
• Thiolase: Uses CoA to release acetyl-CoA

Question 17

Pyruvate Carboxylase

Answer 17

• Uses pyruvate or amino acids to make oxaloacetate

Question 18

Acetyl CoA Carboxylase

Answer 18

• Uses ATP to carboxylate Acetyl-CoA to form Malonyl-CoA
• Malonyl-CoA drives fatty acid synthesis
• Regulated by phosphorylation
• Inhibited with rising glucagon and AMP
• Citrate stimulates ACC

Question 19

Fatty Acid Synthase

Answer 19

• Used in fat synthesis
• 4 step reaction
• Uses up 2 NADPH and release H2O

Question 20

HMG-CoA Reductase

Answer 20

• Used in cholesterol synthesis
• Uses NADPH and ATP to make cholesterol from Acetyl-CoA in the cytoplasm

Question 21

Lecithin: Cholesterol Acyl Transferase Enzyme(LCAT)

Answer 21

• Used by HDL to pick up cholesterol esters and return them to the liver

Question 22

Lactate Dehydrogenase

Answer 22

• Used for anaerobic metabolism
• Converts pyruvate to lactate
• Converts NADH to NAD+ so glycolysis can continue

Question 23

Pyruvate Carboxylase

Answer 23

• Used in gluconeogenesis
• Uses ATP and adds bicarbonate onto pyruvate to form oxaloacetate

Question 24

PEP Carboxykinase

Answer 24

• Used in gluconeogenesis
• Uses oxaloacetate to form PEP

Question 25

Fructose 1,6 Bisphosphatase

Answer 25

• Used in gluconeogenesis
• Reverses step 3 of glycolysis(PFK-1)
• Converts Fructose 1,6-bisphosphate to Fructose 6-phosphate

Question 26

Glucose 6-phosphatase

Answer 26

• Used in gluconeogenesis
• Hydrolyzes off phosphate to produce glucose

Question 27

PFK-2/FBPase-2

Answer 27

• Tandem enzyme that controls formation and hydrolysis of Fructose 2,6-bisphosphate
• Two active sites that can be reciprocally regulated via phosphorylation
• Unphosphorylated phosphorylates F6P to make F2,6P -> Glycolysis active
• Phosphorylated hydrolyzes F2,6P to make F6P -> GNG active