BACKGROUND: Recent studies of melanin biosynthesis have uncovered an unusual enzymatic activity which converts the non-naturally occurring D-isomer of 2-carboxy-2,3-dihydroindole-5,6-quinone (dopachrome) into 5,6-dihydroxyindole-2-carboxylic acid (DHICA). The aim of the present investigation was to isolate and characterize the enzyme catalyzing this tautomerization reaction. MATERIALS AND METHODS: After we performed a tissue survey of D-dopachrome tautomerase activity, 10 bovine lenses were homogenized and used as a source of enzyme. A soluble fraction was obtained by high-speed centrifugation and subjected to successive FPLC chromatography on Phenyl-sepharose, Mono S cation-exchange, and Superdex gel-filtration. The isolated enzyme was electrophoresed, blotted onto PVDF membrane, and the N terminus analyzed by gas phase micro-sequencing. RESULTS: The protein catalyzing the conversion of D-dopachrome to DHICA was purified to homogeneity in 14% yield and showed a molecular weight of 12 kD when analyzed by SDS-PAGE. The first 27 amino acid residues of this protein were sequenced and found to be identical with those of bovine macrophage migration inhibitory factor (MIF). The catalytic activity of native MIF was confirmed by studies of purified recombinant human MIF, which showed the same tautomerase activity. While L-dopachrome was not a substrate for this reaction, the methyl esters of the L- and D-isomers were found to be better substrates for MIF than D-dopachrome. CONCLUSIONS: MIF has been described recently to be an anterior pituitary hormone and to be released from immune cells stimulated by low concentrations of glucocorticoids. Once secreted, MIF acts to control, or counter-regulate, the immunosuppressive effects of glucocorticoids on the immune system. Although the tested substrate, D-dopachrome, does not occur naturally, the observation that MIF has tautomerase activity suggests that MIF may mediate its biological effects by an enzymatic reaction. These data also offer a potential approach for the design of small molecule pharmacological inhibitors of MIF that may modulate its potent immunoregulatory effects in vivo.
BACKGROUND: Recent studies of melanin biosynthesis have uncovered an unusual enzymatic activity which converts the non-naturally occurring D-isomer of 2-carboxy-2,3-dihydroindole-5,6-quinone (dopachrome) into 5,6-dihydroxyindole-2-carboxylic acid (DHICA). The aim of the present investigation was to isolate and characterize the enzyme catalyzing this tautomerization reaction. MATERIALS AND METHODS: After we performed a tissue survey of D-dopachrome tautomerase activity, 10 bovine lenses were homogenized and used as a source of enzyme. A soluble fraction was obtained by high-speed centrifugation and subjected to successive FPLC chromatography on Phenyl-sepharose, Mono S cation-exchange, and Superdex gel-filtration. The isolated enzyme was electrophoresed, blotted onto PVDF membrane, and the N terminus analyzed by gas phase micro-sequencing. RESULTS: The protein catalyzing the conversion of D-dopachrome to DHICA was purified to homogeneity in 14% yield and showed a molecular weight of 12 kD when analyzed by SDS-PAGE. The first 27 amino acid residues of this protein were sequenced and found to be identical with those of bovinemacrophage migration inhibitory factor (MIF). The catalytic activity of native MIF was confirmed by studies of purified recombinant humanMIF, which showed the same tautomerase activity. While L-dopachrome was not a substrate for this reaction, the methyl esters of the L- and D-isomers were found to be better substrates for MIF than D-dopachrome. CONCLUSIONS:MIF has been described recently to be an anterior pituitary hormone and to be released from immune cells stimulated by low concentrations of glucocorticoids. Once secreted, MIF acts to control, or counter-regulate, the immunosuppressive effects of glucocorticoids on the immune system. Although the tested substrate, D-dopachrome, does not occur naturally, the observation that MIF has tautomerase activity suggests that MIF may mediate its biological effects by an enzymatic reaction. These data also offer a potential approach for the design of small molecule pharmacological inhibitors of MIF that may modulate its potent immunoregulatory effects in vivo.
Authors: Yoonsang Cho; Gregg V Crichlow; Jon J Vermeire; Lin Leng; Xin Du; Michael E Hodsdon; Richard Bucala; Michael Cappello; Matt Gross; Federico Gaeta; Kirk Johnson; Elias J Lolis Journal: Proc Natl Acad Sci U S A Date: 2010-06-08 Impact factor: 11.205
Authors: Dan Xin; Beatriz E Rendon; Ming Zhao; Millicent Winner; Arlixer McGhee Coleman; Robert A Mitchell Journal: Mol Cancer Res Date: 2010-11-11 Impact factor: 5.852
Authors: Huzaifa Adamali; Michelle E Armstrong; Anne Marie McLaughlin; Gordon Cooke; Edward McKone; Christine M Costello; Charles G Gallagher; Lin Leng; John A Baugh; Günter Fingerle-Rowson; Richard J Bucala; Paul McLoughlin; Seamas C Donnelly Journal: Am J Respir Crit Care Med Date: 2012-05-16 Impact factor: 21.405
Authors: D V Pastrana; N Raghavan; P FitzGerald; S W Eisinger; C Metz; R Bucala; R P Schleimer; C Bickel; A L Scott Journal: Infect Immun Date: 1998-12 Impact factor: 3.441
Authors: Kristin K Brown; Frances H Blaikie; Robin A J Smith; Joel D A Tyndall; Hongqi Lue; Jürgen Bernhagen; Christine C Winterbourn; Mark B Hampton Journal: J Biol Chem Date: 2009-09-23 Impact factor: 5.157