On the reduced minus oxidized difference spectrum of P-450 in liver microsomes

Effects of experimental diabetes on aminopyrine metabolism in rats

1. The metabolism of aminopyrine has been investigated in normal, alloxan- and streptozotocin (STZ)-diabetic rats. The drug was administered i.p. and the serum concentrations of the unchanged aminopyrine and its main metabolites were measured using h.p.l.c. 2. Aminopyrine was metabolized at a slower rate in both diabetic rats, as judged from higher serum levels of the unchanged drug. Pharmacokinetic studies of aminopyrine in diabetic rats also showed a decrease in serum clearance of the drug and an increase in its serum half-life. 3. The serum concentrations of the metabolites 4-monomethylaminoantipyrine, 4-acetylaminoantipyrine and 4-formylaminoantipyrine decreased in diabetic rats. In contrast, serum levels of 3-hydroxymethyl-2-methyl-4-dimethylamino-1-phenyl-3-pyrazolin-5-on e increased over control values. Serum concentrations of 4-aminoantipyrine remained unaltered by the induction of diabetes. 4. The magnitudes of changes in serum levels of these metabolites were larger in alloxan-diabetes than in STZ-diabetes. 5. Additional support for changed metabolism of aminopyrine was obtained from the investigation of microsomal preparations from diabetic and normal rats. 6. These findings indicate that it is important to use intact animals for evaluation of the metabolism of drugs in pathological states.

Biochemical effects on radioprotective agents on the liver microsomal hydroxylating system: in vitro studies

The action of two radioprotectors--cysteamine and cystamine--on the liver microsomal multi-enzyme hydroxylating system, a key stem in drug and biological compounds metabolism, has been studied. Their effects have been systematically analysed at the level of individual enzyme activities and global functions. The two compounds are quite inactive on NADPH and NADH cytochrome c reductase activities, but slightly denature the cytochrome P450 into cytochrome P420. Furthermore, they do inhibit to some extent (30 per cent at 10(-2) M) the rate of codeine hydroxylation and totally suppress ((at 10(-2) M) the NADPH-induced lipid peroxidation which occurs during enzymatic functioning. These results are discussed in the light of the toxicity of radioprotectors.

The affinity of cytochrome P-450 for ethyl isocyanide: an explanation of double soret spectra

The 2 pH dependent peaks formed in the Soret region by the treatment of reduced hepatic microsomes or purified cytochrome P-448 with ethyl isocyanide do not exhibit identical dependence on ethyl isocyanide concentration. This behavior and other facts regarding double Soret spectra can be explained by a simple expostulation involving lipophilic and corrdinate binding of pi-acceptor ligands.

Study of biological pigments by single specimen derivative spectrophotometry

The single specimen derivative (SSD) method provides an absolute absorption spectrum of a substance in the absence of a suitable reference. Both a reference and a measuring monochromatic beam pass through a single sample, and the specimen itself acts as its own reference. The two monochromatic beams maintain a fixed wavelength difference upon scanning, and the difference in absorbance of the two beams is determined. Thus, the resulting spectrum represents the first derivative of the conventional type absorption spectrum. Tissues and cell fractions have been examined at room and liquid N(2) temperature and chromophoric molecules such as the mitochondrial cytochromes and blood pigments have been detectable in low concentrations. In the case of isolated cellular components, the observed effects of substrates and inhibitors confirm similar studies by conventional spectrophotometry. The extension of the SSD concept to the microscopic level has permitted the study of the tissue compartmentalization and function of cytochromes and other pigments within layered tissue.