Fig. 4

Catabolism of proteinogenic amino acids. a Catabolic routes of amino acids linking to the central metabolism. b Involvement of H donors and H acceptors in Stickland reactions. In the oxidation reaction, alanine, leucine, isoleucine, valine, phenylalanine, tryptophan, and histidine function as H donors to produce acetate, 3-methylbutyrate, 2-methylbutyrate, 2-methylpropionate, phenylacetate, indolacetate, and glutamate, respectively. In the reduction reaction, glycine, proline, phenylalanine, tryptophan, ornithine, and leucine function as H acceptors to produce acetate, 5-aminovalerate, phenylpropionate, indolpropionate, 5-aminovalerate, and 4-methylvalerate, respectively