Tryptophan pyrrole ring cleavage enzymes in placenta.

Tryptophan pyrrole ring cleavage enzymes were assayed in pregnant uterus of mouse. The highest activity was observed at 6.5 days post-coitus (dpc) with a small activity shoulder at 9.5 to 12.5 dpc concepti and placenta. The highest peak at early concepti of 6.5 dpc was coincided with gene expression of tryptophan 2,3-dioxygenase (TDO). And the shoulder from 9.5 dpc was coincided with the expression of indoleamine 2,3-dioxygenase (IDO). These enzymes showed a different inhibitory behavior to a proper IDO inhibitor, 1-methyl tryptophan. In situ hybridization analysis revealed that TDO was expressed in the decidua of the early concepti. This is the first report of the extra hepatic TDO.