Comparative aspects of microsomal cytochrome P-450-dependent monooxygenase activities in musk shrew (Suncus murinus), Mongolian gerbil (Meriones unguiculatus), harvest mouse (Micromys minutus) and rat.

1. The cytochrome P-450 content (0.75 +/- 0.13 nmol/mg microsomal protein) in musk shrew (suncus, Suncus murinus) liver microsomes was lower than that (1.30 +/- 0.26) in rat liver microsomes, but it is approximately the same level as in the Mongolian gerbil (Meriones unguiculatus, 1.18 +/- 0.14), harvest mouse (Micromys minutus, 1.11 +/- 0.02) and rat. 2. The hydroxylation activity (based on cytochrome P-450) of medium-chain fatty acids (otanoic, decanoic, lauric and tridecanoic acids) is much higher in suncus, Mongolian gerbil and harvest mouse than in rat, with the exception of the activity of decanoic and tridecanoic acids in Mongolian gerbil. 3. This suggests that cytochrome P-450 species catalyzing the hydroxylation of medium-chain fatty acids are present in these laboratory animals in higher concentrations. 4. The aminopyrine N-demethylation activity based on microsomal protein or cytochrome P-450 in suncus is significantly lower than that in rat, but the N-demethylation activity in Mongolian gerbil and harvest mouse is approximately 1.7-2.0-fold greater than that in rat.