Occurrence of a cytochrome P-450-containing mixed-function oxidase system in the pond snail, Lymnaea stagnalis

Abstract

1. The occurrence of an as yet unidentified cytochrome P-450 in the microsomal fraction of the digestive gland of the snail, Lymnaea stagnalis was studied.

2. Studies in vivo and in vitro (digestive gland homogenates or the 170 000g fraction) of the cytochrome P-450-mediated metabolism of substrates such as biphenyl, pentoxy-and ethoxy-resorufin and aminopyrine have been made.

3. Cytochrome P-450 concentration in the digestive gland calculated from CO-difference spectra was 0.30 + 0.05 nmol/g tissue. This amount was not increased either by phenobarbital or by 3-methylcholanthrene.

4. Aniline binding spectra resembled normal type II spectra, while type I model substrates such as hexobarbital and 2,2-dichlorobiphenyl showed type 11- or reversed type I-like spectra.

5. O-Deethylation of 7-ethoxyresorufin did not occur, but 7-pentoxyresorufin O-depentylation activity (80.4 + 28.6 pmol resorufin/g per hour) and aminopyrine N-demethylation activity (375 + 96 pmol formaldehyde/g per minute) were demonstrated.

6. 4-Hydroxybiphenyl was the major metabolite of biphenyl, while minor amounts of 2-hydroxybiphenyi were formed (in vivo 63.7 nmol 4-hydroxybiphenyl and 3.33 nmol 2-hydroxybiphenyl per snail per 24 h, after an oral dose of 778.2 nmol biphenyl; in vitro 118. 21 pmol and 21. 9 nmol, respectively (digestive gland homogenate/mg protein, per hoar).

7. The results indicate that the isoenzymes involved in the observed MFO activities resemble isoenzymes P-450b/e.