[Genetic polymorphism of oxidative drug metabolism. Therapeutic and toxicologic implications].
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Three different types of isoenzymes, Am1, Am2 and Am3 have been revealed by polyacrylamide gel electrophoresis (PAG) and affine PAG electrophoresis in artiodactyla. In cattle and pigs Am2 isoenzyme is monomorphic, as shown by PAG electrophoresis, and polymorphic in affine gel separation (two alloenzymes, Am2A and Am2B have been revealed). Some of sheep have no Am2 isoenzyme, which, apparently, account for the presence of minus-allele. Am2 isoenzyme was not detected in Saiga tatarica which are related to sheep. In reindeer, Am2 system is monomorphic, Am3 system is polymorphic, in reindeers, Saiga tatarica and pigs the variability of the latter system being determined by A3A, A3B alleles.
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Platelet glycoprotein (GP) Ib from 131 healthy Japanese was analyzed using SDS-polyacrylamide gel electrophoresis and specific staining with peroxidase-coupled wheat germ agglutinin after it was transferred to nitrocellulose membranes. Four slightly different species of GPIb were observed and designated as A, B, C, and D for glycoproteins with molecular weights of 168,000, 162,000, 159,000, and 153,000 daltons, respectively. The respective gene frequencies were calculated to be .073, .011, .561, and .355 for A-, B-, C-, D-type GPIb. Portions from each type of GPIb molecule (alpha-chain and glycocalicin) showed heterogeneity with the same molecular weight difference, indicating that the variance would be derived from the polypeptide portion that is exposed to the outer medium. The different types of GPIb were the same with respect to their accessibility to lactoperoxidase, reactivity to lectins, and affinity to TLCK-thrombin. Although Bolin et al reported patients with a bleeding tendency whose platelets have double GPIb bands, here we found that platelets with different GPIb phenotypes showed no significant differences in aggregating activity and platelet retention. Analysis of GPIb phenotype should be important for structural and physiologic studies on GPIb and glycocalicin.
Southern blot analysis suggests that multiple sequences homologous to a phenobarbital-inducible cytochrome P-450 cDNA are present in the rat and mouse genomes. A cDNA (pP-450b-5) to a major phenobarbital-inducible cytochrome P-450 mRNA species in the rat detected 6 polymorphic DNA fragments when hybridized to DNA from C57BL/6J and DBA/2J mice restricted with endonucleases EcoRI, BamHI, and PvuII. Using the BXD recombinant inbred strains, five of these polymorphisms were mapped to the Coh (coumarin hydroxylase) locus on chromosome 7 of the mouse. The Coh locus has previously been shown to code for a phenobarbital-inducible enzyme, believed to be a cytochrome P-450, which catalyzes the conversion of coumarin to 7-hydroxycoumarin (umbelliferone). The DNA polymorphisms appear to reflect changes in either cytochrome P-450 genes or pseudogenes that are very closely linked to the gene responsible for differential coumarin hydroxylase in mice or it may represent a change(s) in the Coh gene itself. The region of the Coh locus on chromosome 7 may be the site of a cluster of cytochrome P-450 genes.
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Hepatic microsomal epoxide hydrolase activity (EC 3.3.2.3), assayed using styrene oxide as the substrate, has a pH optimum of 9.5 from C57BL/6J mice and a pH optimum of 8.7 from DBA/2J mice. In cross and back-cross matings between C57BL/6J and DBA/2J mice, this phenotypic difference in epoxide hydrolase activity is inherited as a single autosomal trait, with co-dominant expression in heterozygotes. Heating liver microsomes from C57Bl/6J mice at 62 degrees C for 30 min produced a slight decrease in enzyme activity, whereas the same treatment of DBA/2J microsomes reduced enzyme activity to less than 3% of its initial value. Twenty-six inbred strains of mice were examined and separated into two phenotypic classes on the basis of differences in pH optima and heat sensitivity of microsomal epoxide hyrolase activity. Eph-1 is proposed as the locus symbol of the structural gene for microsomal epoxide hydrolase, with superscripts b and d designating the alleles carried by C57BL/6J and DBA/2J mice, respectively. Using 24 recombinant inbred strains derived from C57BL/6J and DBA/2J mice, Eph-1 was found to be linked to two loci on Chromosome 1.
N-Acetylation and debrisoquine hydroxylation phenotypes were determined in 54 patients with Gilbert's syndrome and in 247 (sulfamethazine) and 76 (debrisoquine) non-related healthy volunteers, respectively. 40 (74.1%) of the patients and 135 (54.7%) of healthy volunteers were slow acetylators (chi 2 = 6.87). In patients, the cumulative urinary excretion (CUE) of sulfamethazine (0-6 hours) was significantly reduced. No differences between the debrisoquine poor metabolizers were observed: Gilbert's syndrome 5/54 (9.3%), healthy volunteers 5/76 (6.6%). The metabolic ratios were similar in both groups as well as the CUE of debrisoquine and its metabolite. Gilbert's syndrome seems to be related in some way to N-acetylation but not to debrisoquine hydroxylation polymorphism.