Metabolism (summary)

  • Metabolism sites
Mitochondria Fatty acid oxidation (β-oxidation), acetyl- CoA production, TCA cycle, oxidative phosphorylation, ketogenesis.
Cytoplasm Glycolysis, HMP shunt, and synthesis of steroids (SER), proteins (ribosomes, RER), fatty acids, cholesterol, and nucleotides.
Both Heme synthesis, Urea cycle, Gluconeogenesis. HUGs take two (ie, both).
  • Enzyme terminology. An enzyme’s name often describes its function. For example, glucokinase is an enzyme that catalyzes the phosphorylation of glucose using a molecule of ATP. The following are commonly

used enzyme descriptors.

Kinase Catalyzes transfer of a phosphate group from a high-energy molecule (usually ATP) to a substrate (eg, phosphofructokinase).
Phosphorylase Adds inorganic phosphate onto substrate without using ATP (eg, glycogen phosphorylase).
Phosphatase Removes phosphate group from substrate (eg, fructose-1,6-bisphosphatase).
Dehydrogenase Catalyzes oxidation-reduction reactions (eg, pyruvate dehydrogenase).
Hydroxylase Adds hydroxyl group (−OH) onto substrate (eg, tyrosine hydroxylase).
Carboxylase Transfers CO2 groups with the help of biotin (eg, pyruvate carboxylase).
Mutase Relocates a functional group within a molecule (eg, vitamin B12–dependent methylmalonyl-CoA mutase).
Synthase/synthetase Joins two molecules together using a source of energy (eg, ATP, acetyl CoA, nucleotide sugar).
  • Rate-determining enzymes of metabolic processes
Glycolysis Phosphofructokinase-1 (PFK-1) AMP ⊕, fructose-2,6-bisphosphate ⊕,

ATP ⊝, citrate ⊝

Gluconeogenesis Fructose-1,6-bisphosphatase Citrate ⊕

AMP ⊝, fructose-2,6-bisphosphate ⊝

TCA cycle Isocitrate dehydrogenase ADP ⊕

ATP ⊝, NADH ⊝

Glycogenesis Glycogen synthase Glucose-6-phosphate ⊕, insulin ⊕, cortisol ⊕ Epinephrine ⊝, glucagon ⊝
Glycogenolysis Glycogen phosphorylase Epinephrine ⊕, glucagon ⊕, AMP ⊕ Glucose-6-phosphate ⊝, insulin ⊝, ATP ⊝
HMP shunt Glucose-6-phosphate dehydrogenase (G6PD) NADP+ ⊕

NADPH ⊝

De novo pyrimidine synthesis Carbamoyl phosphate synthetase II ATP ⊕, PRPP ⊕

UTP ⊝

De novo purine

synthesis

Glutamine-phosphoribosylpyrophosphate

(PRPP) amidotransferase

AMP ⊝, inosine monophosphate (IMP) ⊝,

GMP ⊝

Urea cycle Carbamoyl phosphate synthetase I N-acetylglutamate ⊕
Fatty acid synthesis Acetyl-CoA carboxylase (ACC) Insulin ⊕, citrate ⊕

Glucagon ⊝, palmitoyl-CoA ⊝

Fatty acid oxidation Carnitine acyltransferase I Malonyl-CoA ⊝
Ketogenesis HMG-CoA synthase Insulin ⊕, thyroxine ⊕

Glucagon ⊝, cholesterol ⊝

Cholesterol synthesis  HMG-CoA reductase Insulin ⊕, thyroxine ⊕

Glucagon ⊝, cholesterol ⊝

 

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