Fig. 2

Effect of a therapeutic dog food on tryptophan metabolism. (A) Relative abundance measurements plotted over time for tryptophan in feces (black circles, left) and serum (orange circles, right). Gray line indicates a statistical model consisting of a quadratic fit plateauing at day 14. Orange line indicates a quadratic fit. (B) Tryptophan pathway schematic indicating where on the molecule the first reaction step acts upon to generate catabolites in the indicated pathway—kynurenine through pyrrole ring cleavage, serotonin through 5′ hydroxylation, and indole through chemistries leaving the side chain intact. (C) Simplified projection of fecal metabolite and inferred functional metagenomic measurements on the KEGG tryptophan pathway map (KO00380) [25–27]. Significantly increased and decreased enzymatic functions and metabolites are depicted in green and red, respectively, while observed but unchanged functions and metabolites are rendered grey. Likely catabolic paths discussed in the text are indicated with blue arrows