Cytochrome b5, Not Superoxide Anion Radical, Is a Major Reductant of Indoleamine 2,3-Dioxygenase in Human Cells

Abstract

The heme protein indoleamine 2,3-dioxygenase (IDO) initiates oxidative metabolism of tryptophan along the kynurenine pathway, and this requires reductive activation of Fe . plays a major role in the activation of IDO in human cells.Human indoleamine 2,3-dioxygenase (IDO) 3 is a cellular enzyme that catalyzes the initial step of the oxidative metabolism of L-tryptophan (L-Trp) along the kynurenine pathway (1, 2). IDO cleaves the pyrrole ring of L-Trp to N-formyl-kynurenine by incorporating molecular oxygen. Although L-Trp is preferred, the enzyme can use other indoleamines such as tryptamine and serotonin as substrates. IDO is expressed constitutively in a limited number of human tissues (3) and also in rabbit enterocytes (4), but in most tissues and cells, expression of the enzyme requires induction, with the pro-inflammatory cytokine interferon-␥ (IFN␥) playing a major role (2). The true physiological function of IDO is becoming clearer, with its induction and the formation of kynurenine pathway metabolites implicated in various physiological and pathological processes, such as in the defense against microbes and tumors, immune regulation, neuropathology, and antioxidant activity (2).IDO is a monomeric protein of 42-kDa molecular mass and contains protoporphyrin IX as its sole prosthetic group (4).

NADH Oxidase Activity of Indoleamine 2,3-Dioxygenase

“…We (15) and others (16) have proposed that IDO is maintained in the active, reduced state in vivo by the action of cytochrome b 5 and cytochrome b 5 reductase as reported for hemoglobin (17,18) and possibly myoglobin (19). Cytochrome P450 reductase and cytochrome b 5 have also been used to develop assays for IDO activity (20), but evidence that cytochrome P450 reductase performs this function in vivo is currently lacking.…”

Tryptophan/kynurenine metabolism in human leukocytes is independent of superoxide and is fully maintained in chronic granulomatous disease

“…dismutase (SOD) does not lower kynurenine production in human cells. 19 Our data show that human CGD peripheral blood cells produce normal levels of kynurenine in response to IFN␥ treatment. While we cannot exclude a role of O 2 .…”

“…The general MS conditions were as follows: spray voltage, 4800 V; sheath and auxiliary gas, nitrogen; sheath gas pressure, 49 arbitrary units; auxiliary gas pressure, 25 arbitrary units; ion transfer capillary temperature, 350°C; collision gas pressure, argon; collision gas pressure, 1.5 mTorr; scan width, 0.70 u; scan time, 0.03 s; Q1 peak width, 0.7 u full-width half-maximum (fwhm); Q3 peak width, 0.70 u fwhm. The collision energy voltages for PA, D4-PA, QA, 3-HKYN, KYN, D6-KYN, AA, TRP, and D5-TRP were 19,19,28,18,26,26,10,21, and 21, respectively.…”

Indol-2-yl ethanones as novel indoleamine 2,3-dioxygenase (IDO) inhibitors

“…The spots were visualized by ultraviolet light (wavelengths 254 and 366 nm). 1 H NMR spectra were recorded in DMSO-d 6 solutions on a Jeol JNM EX 400 machine at 400 MHz with tetramethylsilane (TMS) as internal standard. 13 C and 19 F NMR spectra were recorded on the same machine in DMSO-d 6 solutions at 100 MHz and 376.2 MHz, respectively.…”

“…Cytochrome b 5 has been demonstrated to play this role in vivo. 6,7 By depleting Trp locally, IDO blocks the proliferation of T lymphocytes, which are sensitive to Trp shortage. 8 The downstream catabolites of the kynurenine pathway exacerbate this immunosuppressive effect 1 and are also involved in other pathological conditions, particularly in the nervous system.…”