Publication Cover
Xenobiotica
the fate of foreign compounds in biological systems
Volume 20, 1990 - Issue 8
20
Views
5
CrossRef citations to date
0
Altmetric
Original Article

Mechanism of formation of 6-amino-5-(N-methylformylamino)-1-methyluracil and 3,7-dimethyluric acid from theobromine in the rat in vitro: involvement of cytochrome P-450 and a cellular thiol

, &
Pages 823-833 | Received 05 Apr 1988, Accepted 21 Apr 1990, Published online: 27 Aug 2009
 

Abstract

1. The involvement of glutathione (GSH) and cytochrome P-450 in the conversion of theobromine to 6-amino-5-(N-methylformylamino)-1-methyluracil (3,7-DAU) and 3,7-dimethyluric acid (3,7-DMU) has been investigated in rat liver microsomal incubations.

2. The ratio of formation of 3,7-DAU to 3,7-DMU increased with increasing GSH concentration, reaching a maximum (approximately 12:1) at 2mm. For any given added GSH concentration the formation of 3,7-DAU plus 3,7-DMU remained constant.

3. 3,7-DAU and 3,7-DMU formation were increased approx. 12- and 1.6-fold in liver microsomes from rats treated with 3-methylcholanthrene and phenobarbitone, respectively. Cimetidine, metyrapone and SKF-525A each inhibited the conversion of theobromine to 3,7-DAU and 3,7-DMU.

4. Apparent Km and V,max values for the combined formation of 3,7-DAU and 3,7-DMU were the same in the absence and presence of GSH, 2mm.

5. l-Cysteine and N-acetyl-l-cysteine were as effective as GSH in causing a shift from 3,7-DMU to 3,7-DAU formation, but the non-thiol reducing agents ascorbic acid and α-tocopherol were ineffective.

6. Data are consistent with the hypothesis that 3,7-DAU and 3,7-DMU are derived from a common oxidized intermediate of theobromine, the formation of which is rate-limiting. The putative intermediate normally serves as a precursor to 3,7-DMU but in the presence of GSH. or some other cellular thiol, it may be reduced to give 3,7-DAU.

Reprints and Corporate Permissions

Please note: Selecting permissions does not provide access to the full text of the article, please see our help page How do I view content?

To request a reprint or corporate permissions for this article, please click on the relevant link below:

Academic Permissions

Please note: Selecting permissions does not provide access to the full text of the article, please see our help page How do I view content?

Obtain permissions instantly via Rightslink by clicking on the button below:

If you are unable to obtain permissions via Rightslink, please complete and submit this Permissions form. For more information, please visit our Permissions help page.