Skin L-Tryptophan-2,3-Dioxygenase and Rat Hair Growth

The study identified a new enzyme, skin l-tryptophan-2,3-dioxygenase (skin TDO), which catalyzed the degradation of l-tryptophan into formylkynurenine in rats. The enzyme's activity peaked at 5 to 6 weeks after birth and again at 10 to 11 weeks in depilated rats. Skin TDO's properties were more similar to hepatic TDO than to indoleamine 2,3-dioxygenase. While l-tryptophan injections increased skin TDO activity, hydrocortisone and α-methyl-dl-tryptophan did not affect it. The enzyme's molecular weight was estimated at 16.0 kDa. Increased hair growth rates were associated with higher skin TDO activity, suggesting that skin TDO might play a significant role in initiating or suppressing rat hair growth.