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Xenobiotica
the fate of foreign compounds in biological systems
Volume 20, 1990 - Issue 6
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Original Article

Kinetic characteristics of UDP-glucuronosyltransferases towards a dithiol metabolite of malotilate in hepatic microsomes of rats and rabbits

Pages 619-627 | Received 17 Oct 1989, Accepted 15 Feb 1990, Published online: 27 Aug 2009
 

Abstract

1. The kinetic activity of UDP-glucuronosyltransferases (UDPGT) towards a dithiol metabolite of malotilate, 2,2-di(isopropoxycarbonyl)ethylene-1,1-dithiol, was investigated using rat and rabbit hepatic microsomes. The thio-glucuronide formed was analysed by h.p.l.c. The Km values obtained using rat and rabbit UDPGT were 36.3 ± 3.3 and 443 ± 43 μM, respectively. The Vmax values were 7.14±0.61 and 29.2 ± 6.4 nmol/min per mg (mean ± SD, n = 3).

2. Phenobarbital, an inducer of the GT2 isoform of UDPGT, increased rat microsomal UDPGT activity towards the dithiol. In inhibitory studies, menthol and borneol (specific substrates for GT2a isoform) competitively inhibited glucuronidation of the dithiol. Thus it was concluded that formation of the thio-glucuronide was catalysed mainly by the GT2a isozyme of UDPGT, which is involved in glucuronidation of monoterpenoid alcohols.

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