Species variations in the renal and hepatic conjugation of 3-phenoxybenzoic acid with glycine

1. 3-Phenoxy[¹⁴C]benzoyl-CoA has been chemically synthesized, purified and characterized by field-desorption mass spectrometry. Biological activity of the purified thioester was > 92%.

2. The two enzymic steps involved in the conjugation of 3-phenoxybenzoic acid (3PBA) with glycine have been investigated in hepatic and renal tissues from various mammalian species.

3. A 10- to 300-fold excess of acyl-CoA: glycine N-acyltransferase activity as compared with acyl-CoA synthetase activity was found in most tissue preparations, while the rate of the activating step matched that of the overall process. This suggests that formation of the acyl-CoA thioester (3PBA-CoA) is the rate-limiting step in the conjugation of 3PBA with glycine.

4. In most of the species tested, renal activities were higher than those of corresponding liver preparations.

5. The gerbil and ferret, which excrete 3-phenoxybenzoylglycine as the principal urinary metabolite of 3PBA, gave the highest 3PBA-CoA synthetase and glycine N-acyltransferase activities in vitro. By contrast, the hamster, which excretes only small amounts of the glycine conjugate of 3BPA, had the lowest enzymic activities in vitro.

6. In the mouse and rat there were differences between the patterns of metabolism found in vivo and in vitro, and possible reasons for this are discussed.