Substrate specificity for isomerase activity of macrophage migration inhibitory factor and its inhibition by indole derivatives.
Macrophage migration inhibitory factor (MIF) was discovered as a cytokine that inhibits random migration of macrophages and concentrates them at inflammatory loci. We recently reported the tertiary structure of MIF, and revealed its similarity to that of 5-carboxymethyl-2-hydroxymuconate isomerase. Moreover, MIF was found to have isomerase activity converting D-dopachrome, a stereoisomer of naturally-occurring L-dopachrome, to 5,6-dihydroxyindole-2-carboxylic acid. In this study, we examined the effects of a series of compounds analogous to D-dopachrome on the enzyme activity to obtain vital information for identification of a natural substrate of MIF. Adrenochrome, lacking a carboxyl group at position 2 of the indolinequinone ring, could not be a substrate. Several indole-ring-containing compounds with a carboxyl group were inhibitory to D-dopachrome isomerase activity, of which indole-3-acrylic acid was the most potent inhibitor, with an inhibitor constant (Ki) of 2.8 mM. 2,3-Indolinedione, which lacks a complete indole ring or a carboxyl group but has carbonyl groups at positions 2 and 3, apparently inhibited the enzyme activity in a competitive or mixed manner with a Ki of 0.9 mM. Taken together, these facts suggest that the 2-carboxyl group of the substrate is essential for interaction with the active site of MIF.
Suzuki
M
M
Central Research Institute, Hokkaido University School of Medicine, Sapporo.
Sugimoto
H
H
Tanaka
I
I
Nishihira
J
J
D000323:Adrenochrome / Q000494:pharmacology; D000818:Animals; D045563:Indolequinones; D007211:Indoles / Q000494:pharmacology*; D019746:Intramolecular Oxidoreductases / Q000378:metabolism; D007535:Isomerases / Q000378:metabolism*; D007536:Isomerism; D008263:Macrophage Migration-Inhibitory Factors / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D011809:Quinones / Q000494:pharmacology; D051381:Rats; D013379:Substrate Specificity / Q000187:drug effects
D045563:Indolequinones; D007211:Indoles; D008263:Macrophage Migration-Inhibitory Factors; D011809:Quinones; C001123:dopachrome; D000323:Adrenochrome; D007535:Isomerases; D019746:Intramolecular Oxidoreductases; C042501:dopachrome isomerase