Enzyme activities and metabolites along the kynurenine pathway in mice with Harding-Passey melanoma.

Tryptophan metabolism has been studied in mice with Harding-Passey melanoma and in controls, after a load of 1.0 g/kg b.w. of L-tryptophan by determining ten urinary metabolites of the kynurenine pathway and some enzyme activities involved in the degradation of this aminoacid. Kynurenine was the only tryptophan derivative excreted in significantly higher quantities in mice with melanoma with respect to the controls. This result is in agreement with a significantly higher activity of hepatic tryptophan pyrrolase in mice with melanoma. Liver kynureninase and liver and kidney kynurenine aminotransferase activities were similar in the two groups of mice. These findings point to a possible role of tryptophan in the biogenesis of melanins in pathological conditions such as in melanoma.