Mersalyl oxide

Melarsoprol [me LAR soe prole] is a derivative of mersalyl oxide, a trivalent arsenical. 

Fia. 27. Absorption spectra of succinate dehydrogenase (A), its larger subunit (B), and its smaller subunit (C). (A) Trace 1, oxidized succinate dehydrogenase trace 2, flavin contribution to the spectrum of oxidized enzyme trace 5, iron-sulfur contribution to the spectrum of oxidized enzyme trace 4, oxidized enzyme treated with dithionite trace 3, oxidized enzyme treated with sodium mersalyl and dithio-nite. Protein = 1.48 mg/ml. (B) Trace 1, oxidized trace 2, flavin contribution to trace 1 trace 3, after treatment of 1 with sodium mersalyl and dithionite. Protein = 3.0 mg/ml. (C) Trace 1, oxidized trace 2, after treatment with mersalyl trace 3, after treatment of 2 with dithionite. Protein = OA mg/ml. From Davis and Hatefi U43). 

Fia. 9. Spectral characteristics of the soluble NADH dehydrogenase (1.6 mg/ml) isolated from complex I. Traces 1, spectrum of oxidized enzyme 2, NADH-reduced enzyme S, dithionite-reduced enzyme 4, flavin contribution to 1 after destruction of ironnsulfur chromophore with sodium mersalyl 3, iron-sulfur contribution to 1 obtained by subtraction of 4 from 1 6, 4 ilus dithionite showing that after destruction of the iron-sulfur chromophore with mersalyl and reduction of flavin with dithionite the enzyme has no absorption in the visible region. From Hatefi and Stempel (40). 

The role of siroheme in the reduction of nitrite is supported by the observation that nitrite perturbs the spectrum of the oxidized or reduced enzyme. Carbon monoxide reaction with the reduced siroheme can be followed spec-trophotometrically. The complex can be dissociated with oxygen. The kinetics of CO-complex formation and dissociation correspond with those for CO inhibition of nitrite reductase. The inhibition of nitrite reductase by p-chloromercuribenzoate, phenyl mercury acetate, and sodium mersalyl demonstrate the involvement of SH groups presumably associated with cysteine residues found in nitrite reductase. Epr studies and spectral data indicate the oxidation/reduction of iron sulfur centers and the formation of a NO-heme complex however, other intermediates have not been confirmed (Aparicio et al., 1975 Vega and Kamin, 1977 Hucklesby et al., 1979). 

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