Enzymes of Metabolism Flashcards
Lactate Dehydrogenase
Lactate + NAD –> pyruvate + NADH
Pyruvate Dehydrogenase
Pyruvate –> acetyl coA
Allows pyruvate to enter TCA cycle
Hexokinase
Glucose –> glucose-6-phosphate
Found in non-liver cells
Requires ATP and is stimulated by insulin
Glucokinase
Glucose –> glucose-6-phospate
Found in the liver
Requires ATP and is stimulated by insulin
Phosphofructokinase 1
Enzyme of the committed step of glycolysis
Begins the series of reactions that results in acetyl coA –> 2 pyruvate, 2 ATP, 2 NADH (OR lactate + NAD+ in anaerobic metabolism)
Stimulated by high [AMP] and by insulin.
Inhibited by high [ATP], high [citrate], and by glucagon.
Pyruvate Carboxylase
Pyruvate –> oxaloacetate (creation of oxaloacetate is anaplerotic! Adds to TCA)
Glutamate hydrogenase
Glutamate + pyruvate –> a-ketoglutarate + alanine
Requires B6
a-ketoglutarate is a TCA intermediate, so a reaction producing it is anaplerotic.
Phosphoenolpyruvate carboxylase
Oxaloacetate –> glyceraldehyde 3 ( DHAP).
This is an important enzyme in gluconeogenesis and is also involved in generating glycerol from pyruvate (glycerol needed for TAG synthesis)
Also called PEPCK
Fructose-1-6-biphosphatase
F-1-6-BiP –> F-6-P
Important step in gluconeogenesis
Glucose-6-Phosphatase
G-6-P –> glucose
Important step in gluconeogenesis
Exists in liver cells (NOT skeletal muscle)
Without removing the phosphate group, glucose would not be able to travel outside of the cell it was made in
Phosphoglucomutase
G-6-P –> G-1-P
Important step in glycogen synthesis and glycogenolysis
Moves the phosphate group
Branching enzyme
Adds branches via a-1-6 bonds during glycogen synthesis
Glycogen synthase
Adds more glucose monomers via a-1-4 bonds during glycogen synthesis
Debranching enzyme
Cleaves a-1-6 bonds in glycogen, breaking branches
Stimulated by glucagon and epinephrine
Important step in glycogenolysis
Glycogen phosphorylase
Cleaves a-1-4 bonds in glycogen, pulling apart glucose monomers –> G-1-P
Important step in glycogenolysis
Glutathione reductase
Facilitates the e- donation from NADPH to glutathione
Important enzyme in ROS neutralization
Glutathione peroxidase
Hydrogen peroxide + glutathione –> H20
Facilitates the e- donation from glutathione to hydrogen peroxide
Important enzyme in ROS neutralization
Hormone-sensitive-lipase
Breaks down TAGs into 3 fatty acids + glycerol
Stimulated by glucagon, epinephrine, or ACTH
Inhibited by insulin
Important step in fatty acid oxidation
Carnitine-palmitoyl transferase I
CPT I
Fatty acyl CoA + carnitine –> fatty acyl carnitine + CoA
Important step in fatty acid oxidation because fatty acyl coA needs a 2-phase “carnitine shuttle” to get into mitochondrial matrix
- Inhibited by malonyl CoA (produced during fatty acid synthesis) and insulin
- Stimulated by AMP-PK
Carnitine-palmitoyl transferase II
CPT II
Fatty acyl carnitine + CoA –> fatty acyl coA + carnitine
Important step in fatty acid oxidation because fatty acyl coA needs a 2-phase “carnitine shuttle” to get into mitochondrial matrix
Carnitine travels back to outer mitochondrial membrane to be recycled by the shuttle
Dynamics of malonyl coA regulation
Malonyl coA is an important regulator of fatty acid synthesis and oxidation
It is created as an intermediate during fatty acid synthesis
High levels of malonyl coA will inhibit CPT I and thus inhibit fatty acid oxidation
It is produced from acetyl CoA —> malonyl coA via the enzyme acetyl CoA carboxylase
Insulin stimulates acetyl coA carboxylase activity via dephosphorylation by PP2, increases malonyl coA, and stimulates fatty acid synthesis (fed = store fat)
Glucagon inhibits acetyl coA carboxylase activity via phosphorylation by AMP-PK, reduces malonyl coA, and stimulates fatty acid oxidation (fasted = burn fat)
Fatty acid synthase
Malonyl coA –> palmitate (a 16-c fatty acid)
Requires 8 acetyl coA and 14 NADPH to create palmitate
Complex enzyme that catalyzes a number of reactions important in fatty acid synthesis.
PP2
Removes phosphate from acetyl coA carboxylase, which activates it and allows fatty acid synthesis to run.
Stimulated by insulin.
Facilitates synthesis of malonyl coA and therefore inhibits fatty acid oxidation.
AMP-PK
Phosphorylates acetyl coA carboxylase, which deactivates it and inhibits fatty acid synthesis.
Stimulated by glucagon.
Inhibits synthesis of malonyl coA and therefore favors fatty acid oxidation.
