Indoleamine 2,3-dioxygenase: antioxidant enzyme in the human eye.
BACKGROUND
Indoleamine 2,3-dioxygenase (IDO) is the first enzyme of the tryptophan degradation pathway. IDO is an antioxidant enzyme because it is a direct scavenger of superoxide radicals. In this study, we measured the activity of IDO in the human eye.


METHODS
IDO was detected in the protein extract of human retina, iris/ciliary body, and lens. The products formed were measured using HPLC with electrochemical detection. Enzyme activity was expressed as the quantity of kynurenine and 3-hydroxykynurenine formed.


RESULTS
IDO activity in the retina extract was 51.5 (+/-10) nmol/g tissue/h, and kynurenine formation was detected. In the iris/ ciliary body, IDO activity was 191.8 (+/49) nmol/g tissue/h, and both kynurenine and 3-hydroxy-kynurenine were formed from tryptophan. In the extract of lens cortex only 3-hydroxykynurenine was formed from tryptophan. IDO activity was 351 (+/-67.3) nmol/g tissue/h.


CONCLUSIONS
Free tryptophan is degradated in the human eye by IDO, an antioxidative enzyme. IDO may be an antioxidant mechanism in the eye.
Malina
H Z
HZ
Laboratoire d'Ophthalmologie Expérimentale, Institut Suisse de Recherche Expérimentale sur le Cancer, Epalinges s/Lausanne, Switzerland.
Martin
X D
XD
D000368:Aged; D000369:Aged, 80 and over; D000975:Antioxidants / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D002924:Ciliary Body / Q000201:enzymology; D005123:Eye / Q000201:enzymology*; D006801:Humans; D006900:Hydroxylation; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D007498:Iris / Q000201:enzymology; D007737:Kynurenine / Q000378:metabolism; D050601:Kynurenine 3-Monooxygenase; D007908:Lens, Crystalline / Q000201:enzymology; D006899:Mixed Function Oxygenases / Q000378:metabolism; D012160:Retina / Q000201:enzymology; D014364:Tryptophan / Q000378:metabolism; D014366:Tryptophan Oxygenase / Q000378:metabolism*
D000975:Antioxidants; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D007737:Kynurenine; D014364:Tryptophan; D006899:Mixed Function Oxygenases; D014366:Tryptophan Oxygenase; D050601:Kynurenine 3-Monooxygenase