- 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 ⊝ |