Mode or inhibition or rat liver tryptophan 2,3-dioxygenase by melatonin
Article first published online: 30 JAN 2007
Journal of Pineal Research
Volume 16, Issue 4, pages 188–192, May 1994
How to Cite
Walsh, H. A., Daya, S. and Whiteley, C. G. (1994), Mode or inhibition or rat liver tryptophan 2,3-dioxygenase by melatonin. Journal of Pineal Research, 16: 188–192. doi: 10.1111/j.1600-079X.1994.tb00100.x
- Issue published online: 30 JAN 2007
- Article first published online: 30 JAN 2007
- Received November 17, 1993; accepted March 8, 1994.
- tryptophan 2;
- pineal gland;
- competitive inhibition;
- substrate inhibition
Walsh HA, Daya S, Whiteley CG. Mode of inhibition of rat liver tryptophan 2,3-dioxygenase by melatonin. J. Pineal Res. 1994:16:188–192.
Liver tryptophan 2,3-dioxygenase is a cytosolic enzyme that plays a crucial role in the regulation of circulating levels of tryptophan. Stimulation of the activity of this enzyme by heme enhances the catabolism of tryptophan, making less tryptophan available for uptake into the brain. Melatonin, the major hormone of the pineal gland, is shown to cause competitive inhibition of this enzyme (Ki = 2. 70 μM). This structural analog of the substrate L-tryptophan is a negative homotropic cooperative modulator of the enzyme. The enzyme has a Km = 100 μM, and the substrate concentration required for optimum activity was found to be 2. 5 mM with substrate inhibition becoming a feature at higher levels of tryptophan.