S-oxygenation of N-substituted thioureas catalyzed by the pig liver microsomal FAD-containing monooxygenase

doi:10.1016/0003-9861(79)90397-7

Archives of Biochemistry and Biophysics

Volume 198, Issue 1, November 1979, Pages 78-88

https://doi.org/10.1016/0003-9861(79)90397-7 Get rights and content

Abstract

The microsomal FAD-containing monooxygenase (EC 1.14.13.8, dimethylaniline monooxygenase) purified to homogeneity from hog liver catalyzes NADPH- and oxygen-dependent S-oxygenation of phenylthiourea, ethylenethiourea, thiocarbanilide, N-methylthiourea, and thiourea to their corresponding formamidine sulfinic acids. The sulfinic acids are formed by sequential enzymic oxidation of the thioureas through intermediate sulfenic acids. The reaction sequence was established by separating intermediate and final oxygenated metabolites of phenylthiourea and ethylenethiourea. The sulfenic and sulfinic acids of these two thioureas, produced enzymically, were chromatographically and spectrally identical with chemically synthesized reference compounds. Phenylformamidine and ethyleneformamidine sulfinic acids are slowly converted to their sulfonic acids upon prolonged incubation. While N-substituted formamidine sulfinic acids oxidize spontaneously to formamidine sulfonic acids at 37 °C, the further oxidation of ethyleneformamidine sulfinic acid may be, at least in part, enzyme catalyzed. The purified monooxygenase also catalyzes rapid oxygenation of mercaptoimidazoles to the corresponding imidazole sulfinic acids. The instability of S-oxygenated mercaptoimidazoles prevented their isolation and positive identification, but analysis of kinetic data obtained with sulfenic acid trapping agents suggests that these compounds are oxygenated by the same reaction sequence established for N-substituted thioureas. The NADPH- and oxygen-dependent oxidation of thiocarbamates and of 2-mercaptoimidazoles catalyzed by hog or hamster liver microsomes correlates with dimethylaniline N-oxidase activity and appears completely independent from cytochrome P-450. The S-oxidation of thiourea and its derivatives is not inhibited by n-octylamine, a known inhibitor of cytochrome P-450 dependent oxygenations. Furthermore, differential thermal inactivation of the flavin-containing monooxygenase totally abolishes phenylthiourea S-oxidase activity of hamster liver microsomes.

References (34)

C.P. Richter
J. Thoracic Surg
(1952)
R.R. Dalvi et al.
Life Sci
(1974)
A.L. Hunter et al.
Biochem. Pharmacol
(1975)
L.L. Poulsen et al.
Biochem. Pharmacol
(1974)
G.H. Hogeboom et al.
J. Biol. Chem
(1948)
D.M. Ziegler et al.
D.M. Ziegler et al.
Biochem. Biophys. Res. Commun
(1964)
L.C. Chesley
J. Biol. Chem
(1944)
W.S. Allison et al.
Arch. Biochem. Biophys
(1970)
R.A. Prough et al.
Arch. Biochem. Biophys
(1977)

C.P. Richter

J. Am. Med. Ass

(1945)

S.H. Dicke et al.

J. Pharm. Exp. Ther

(1945)

S.H. Dicke et al.

S.N. Giri et al.

Arch. Environ. Health

(1970)

R.T. Williams et al.

Ann. N. Y. Acad. Sci

(1965)

J.A. Ruddick et al.

Teratology

(1976)

R.R. Scheline et al.

J. Med. Pharm. Chem

(1961)

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^☆: This work supported in part by NSF Grant AER75-01893A01.

²: Present address: Department of Medicinal Chemistry and Pharmacology, School of Pharmacy, Purdue University, W. Lafayette, Ind. 47907.

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S-oxygenation of N-substituted thioureas catalyzed by the pig liver microsomal FAD-containing monooxygenase☆

Abstract

J. Thoracic Surg

Life Sci

Biochem. Pharmacol