Birds metabolism, species differences

Lewis, D.F.V., Bird, M.G. Parke, D.V. (1997) Molecular modelling of CYP2E1 enzymes Irom rat, mouse and man an explanation for species differences in butadiene metabolism and potential carcinogenicity, and rationalization of CYP2E substrate specificity. Toxicology, 118, 93-113... 

This species difference may be associated with the fact that birds and mammals differ profoundly in their nitrogenous metabolism the bird being uricotelic, arid excreting waste protein nitrogen as uric acid, whereas the mammal is ureotelic, and excretes nitrogen chiefly as urea (p. 378). 

Similarly for wildlife species, differences in physiology have dramatic effects in toxic sensitivity. For example, although peregrine falcons are very sensitive to the eggshell thinning effects of DDT (chapter 2), other species of birds are not impacted. For example, this effect has not been observed in game birds (e.g., chickens, turkeys, quail, pheasants). In many instances, these differences are based on differences in the type, speed, and end products of metabolism across species. 

In rodents, group A-type substrates most likely will be transformed by C YP2B. Planar substrates will be transformed by CYP1A, whereas C- and D-type substrates will not be transformed. Hence, the structure of the compound determines which isozyme will mediate in its transformation. For other species, however, these structural rules may be different. In birds, group A-type substrates are metabolized easily, whereas planar compounds are transformed with great difficulty. 

---