A stable isotope dilution assay for disopyramide and its [13C, 15N]labelled analogue in biological fluids

The mass spectra of disopyramide phosphate and two stable isotopically labelled analogues have been obtained using electron impact and chemical ionization. The low isotopic purity of [13C, 15N)disopyramide phosphate was shown to be due to the low isotopic purity of the 15N label. A stable isotope dilution assay for disopyramide and [13C, 15N]disopyramide in biological fluids has been developed using [2H14]disopyramide phosphate as the internal standard. This assay will be used to analyse samples obtained after the co-administration of disopyramide phosphate intravenously and [13C, 15N]disopyramide phosphate orally to several animal species.     

Measuring Fit of Sequence Data to Phylogenetic Model: Gain of Power Using Marginal Tests

Testing fit of data to model is fundamentally important to any science, but publications in the field of phylogenetics rarely do this. Such analyses discard fundamental aspects of science as prescribed by Karl Popper. Indeed, not without cause, Popper (Unended quest: an intellectual autobiography. Fontana, London, 1976) once argued that evolutionary biology was unscientific as its hypotheses were untestable. Here we trace developments in assessing fit from Penny et al. (Nature 297:197–200, 1982) to the present. We compare the general log-likelihood ratio (the G or G ² statistic) statistic between the evolutionary tree model and the multinomial model with that of marginalized tests applied to an alignment (using placental mammal coding sequence data). It is seen that the most general test does not reject the fit of data to model (P ~ 0.5), but the marginalized tests do. Tests on pairwise frequency (F) matrices, strongly (P < 0.001) reject the most general phylogenetic (GTR) models commonly in use. It is also clear (P < 0.01) that the sequences are not stationary in their nucleotide composition. Deviations from stationarity and homogeneity seem to be unevenly distributed amongst taxa; not necessarily those expected from examining other regions of the genome. By marginalizing the 4 ^t patterns of the i.i.d. model to observed and expected parsimony counts, that is, from constant sites, to singletons, to parsimony informative characters of a minimum possible length, then the likelihood ratio test regains power, and it too rejects the evolutionary model with P ≪ 0.001. Given such behavior over relatively recent evolutionary time, readers in general should maintain a healthy skepticism of results, as the scale of the systematic errors in published trees may really be far larger than the analytical methods (e.g., bootstrap) report.