The deletion of tryptophan peroxidase activity during dye carcinogenesis.

Experiments were performed to determine whether the absence of the enzyme sys tem tryptophan peroxidase (TPO) in transplanted hepatomas was associated with fac tors other than deletion of the apoenzymes, and whether changes in TPO activity and its adaptive response occurred during carcinogenesis with 3'-methyl-4-dimethylaminoazobenzene (3'-Me-DAB). No appreciable TPO activity was observed in two transplanted rat hepatomas (Novikoff and 3'-Me-DAB hepatoma) or in a transplanted mouse hepatoma (Hepatoma 134). Neither the addition of a peroxide-generating sys tem nor the addition of normal liver homogenate was effective in activating the TPO system of the Novikoff hepatoma. There was no evidence that hepatoma homogenate impaired the TPO activity in normal liver homogenate. When the TPO activity of animals fed 0.06 per cent 3'-Me-DAB was determined, the activity was equivalent to