Amino-acid catabolism first removes or transfers nitrogen, then directs the carbon skeleton to a limited set of metabolic entry points. Glucogenic amino acids yield pyruvate or a …
Heme biosynthesis forms protoporphyrin IX and inserts ferrous iron to generate heme, an essential prosthetic group for hemoglobin, myoglobin, cytochromes, catalases, peroxidases, …
Heme degradation disposes of heme released predominantly during turnover of senescent erythrocytes and converts its tetrapyrrole ring into bilirubin for biliary excretion. Macroph…
The methionine cycle activates methionine to S-adenosylmethionine (SAM), the universal major methyl donor for DNA, RNA, protein, phospholipid, neurotransmitter, and small-molecule…
The folate cycle uses tetrahydrofolate (THF) derivatives to carry and distribute one-carbon units at oxidation states ranging from methyl to formyl. These units support de novo pu…
Oxidative deamination releases the amino nitrogen of glutamate as ammonium while regenerating α-ketoglutarate. In the liver this provides mitochondrial ammonia for carbamoyl phosp…
Transamination is the reversible transfer of an α-amino group from an amino acid to an α-keto acid. It funnels nitrogen from most amino acids onto glutamate, while producing carbo…