USE OF A NEW RADIOASSAY FOR TRYPTOPHAN OXYGENASE TO STUDY DEVELOPMENT OF ENZYME IN CHICK EMBRYOS

An assay for the enzyme tryptophan oxygenase has been developed which is approximately ten times more sensitive than previous assays. Radioactive tryptophan labeled at the number 2 carbon atom of the ring is used as substrate. Following the sequential action of tryptophan oxygenase and excess formyl-l-kynurenine formylase, the radioactive carbon is released as formic acid, which is then isolated by passage of the deproteinized incubation mixture through a cation-exchange column. This assay has been used to study the accumulation of tryptophan oxygenase during chick embryogenesis. It was found that accumulation of the enzyme is not linearly related to growth of the embryo or liver tissue, and that there is a large increase in the rate of accumulation, relative to growth, after embryos have reached the age of approximately 11 days (2.5 - 3 g/embryo). This effect was also reflected in an approximately twofold increase in the specific activity of the enzyme during the period from 8 to 13 days of development. © 1968.