Data interpretation factors species difference

In vitro Metabolism. Numerous variables simultaneously modulate the in vivo metabolism of xenobiotics therefore their relative importance cannot be studied easily. This problem is alleviated to some extent by in vitro studies of the underlying enzymatic mechanisms responsible for qualitative and quantitative species differences. Quantitative differences may be related directly to the absolute amount of active enzyme present and the affinity and specificity of the enzyme toward the substrate in question. Because many other factors alter enzymatic rates in vitro, caution must be exercised in interpreting data in terms of species variation. In particular, enzymes are often sensitive to the experimental conditions used in their preparation. Because this sensitivity varies from one enzyme to another, their relative effectiveness for a particular reaction can be sometimes miscalculated. 

If the difference in atomic number between the absorber element and the backscattering element is >10 and if only one kind of element backscatters, EXAFS spectra can be analyzed readily to provide local structural data on adsorbed species. However, because the electron mean free path, thermal and static disorder parameters (Debye-Waller factors), and coordination number for an absorber environment cannot be determined a priori with sufficient accuracy, EXAFS data for suitable reference compounds of known molecular structure must be used to help interpret the EXAFS spectrum for an interfaeial region. 

In summary, in studies of chemical toxicity, pathways and rates of metabolism as well as effects resulting from toxicokinetic factors and receptor affinities are critical in the choice of the animal species and experimental design. Therefore it is important that the animal species chosen as a model for humans in safety evaluations metabolize the test chemical by the same routes as humans and, furthermore, that quantitative differences are considered in the interpretation of animal toxicity data. Risk assessment methods involving the extrapolation of toxic or carcinogenic potential of a chemical from one species to another must consider the metabolic and toxicokinetic characteristics of both species. 

It is suggested that the nickel is bound to a low molecular weight factor, different from F430 of methanogens, and which may involve a corrinoid structure. The nickel is thought to cycle between Ni and Ni , with the CO bound to the metal. ESR data have been interpreted in terms of an Ni species with a bound radical derived from either CO or CO2. The involvement of a nickel-carbon bond has been unequivocally established by isotopic substitution (which is shown in the g = 2.08, 2.02 signals). About 40% of the total nickel is present as this species, suggesting that the Ni—C species is a viable intermediate in the catalytic conversion of CO to CO2. There are parallels with industrial and laboratory catalytic processes, but the involvement of Ni seems... 

Differences in species, gender and experimental design infuence various aspects of ischemia and reperfusion and ultimately the postischemic outcome despite the identical burden of ischemia. These factors should be considered in interpreting experimental data and translating basic research findings to clinical practice. 

---