- 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 ⊝ |