Collect. Czech. Chem. Commun.
1997, 62, 971-980
https://doi.org/10.1135/cccc19970971
Study on N-Demethylation of N,N-Dimethyl-4-aminoazobenzene and N-Nitrosamines by Prostaglandin H Synthase
Marie Stiborováa, Eva Freib and Heinz H. Schmeiserb
a Department of Biochemistry, Charles University, 128 40 Prague 2, Czech Republic
b Department of Molecular Toxicology, German Cancer Research Center, Im Neuenheimer Feld 280, 69120 Heidelberg, Germany
Abstract
The in vitro enzymatic metabolism of carcinogenic N,N-dimethyl-4-aminoazobenzene, N-nitroso-N-methylaniline and N-nitroso-N,N-dimethylamine was investigated using ram seminal vesicle microsomal prostaglandin H synthase. Both N-nitrosamines are not converted by the studied enzyme. Formaldehyde is produced by the prostaglandin H synthase catalyzed reaction from N,N-dimethyl-4-aminoazobenzene. Arachidonic acid and hydrogen peroxide serve as cofactors for the oxidation of N,N-dimethyl-4-aminoazobenzene. The apparent Michaelis constant and the maximal velocity values for N,N-dimethyl-4-aminoazobenzene as a substrate are 64 μmol/l and 51.2 nmol HCHO/min/mg protein, respectively. In addition to formaldehyde, N-methyl-4-aminoazobenzene and 4-aminoazobenzene, two unknown substances are the products of the N,N-dimethyl-4-aminoazobenzene oxidation. The oxidation of N,N-dimethyl-4-aminoazobenzene catalyzed by prostaglandin H synthase is inhibited by glutathione, ascorbate and NADH. The results suggest that prostaglandin H synthase metabolizes N,N-dimethyl-4-aminoazobenzene through a one-electron oxidation mechanism, giving rise to free radicals.
Keywords: Prostaglandin H synthase; Carcinogens; Azo dyes; N-Nitrosamines; N-Demethylation; Radicals.
