Regiochemical differences in cytochrome P450 isozymes responsible for the oxidation of methylenedioxyphenyl groups by rabbit liver

The cytochrome P450 isozymes catalyzing the oxidation of the methylenedioxyphenyl compounds methylenedioxybenzene (MDB) and methylenedioxyamphetamine (MDA) have been investigated in rabbit liver preparations. The aromatic ring in MDB undergoes both demethylenation to catechol and aromatic hydroxylation to sesamol, whereas that in MDA undergoes only demethylenation to dihydroxyamphetamine. Formation of catechol and sesamol from MDB in microsomal incubation mixtures was enhanced about 5- and 3-fold, respectively, by pretreatment of the rabbits with phenobarbital, which induced CYP2B4 and CYP4B1. The cytochrome P450 isozyme responsible for aromatic hydroxylation of MDB was induced by beta-naphthoflavone and was inhibited by alpha-naphthoflavone. Microsomal demethylenation of MDA was minimally sensitive to pretreatment of the rabbits with phenobarbital, beta-naphthoflavone, pyrazole, or rifampicin. However, MDA competitively inhibited the N-demethylation of erythromycin. Antibodies against CYP2B4, but not those against CYP4B1, caused a marked inhibition of the demethylenation and aromatic hydroxylation of MDB. Antibodies against CYP2C3 did not inhibit the demethylenation of MDA, nor did substrates or inhibitors of the CYP2D family except for bufuralol. MDB and MDA were both capable of forming metabolic intermediate complexes, and the rate of complex formation was accelerated by phenobarbital induction. Reconstitution experiments with CYP2B4 suggested that phenobarbital-inducible complex formation from MDA was not due to the carbene pathway involving the methylenedioxy group but was due to oxidation of the amino group. These results indicate that CYP2B4 oxidizes different regions of methylenedioxyphenyl compounds depending on their structure. MDB undergoes oxidation at the methylenedioxy group (major) and the benzene ring (minor). MDA is oxidized at the alkylamino side chain at the nitrogen and alpha-carbon. The results suggested that one or more constitutive isoforms (probably unknown) of cytochrome P450 present in rabbit liver microsomes are primarily responsible for MDA demethylenation but that CYP3A6 contributes slightly.

Molecular cloning of Chinese hamster metallothionein II gene and its 5' flanking region

A genomic DNA clone containing Chinese hamster metallothionein II (MTII) gene and its 5' flanking region was isolated from Cd resistant Chinese hamster ovary (CHO) cells. DNA sequence analysis showed that there are three exons and two introns in the structure of the MTII gene. Further characterization of the 5' flanking region reveals the possible transcription initiation site, metal responsive element and basal-level enhancer sequence. Putatively, this is the promoter region of CHO MTII gene.

Hydroxyl radical mediated demethylenation of (methylenedioxy)phenyl compounds

The oxidative demethylenation reactions of (methylendioxy)phenyl compounds (MDPs), (methylenedioxy)benzene (MDB), (methylenedioxy)amphetamine (MDA), and (methylenedioxy)methamphetamine (MDMA), were evaluated by using two hydroxyl radical generating systems, the autoxidation of ascorbate in the presence of iron-EDTA and the iron-catalyzed Haber-Weiss reaction conducted by xanthine/xanthine oxidase with iron-EDTA. Reaction products generated when MDB, MDA, and MDMA were incubated with the ascorbate or xanthine oxidase system were catechol, dihydroxyamphetamine (DHA), and dihydroxymethamphetamine (DHMA), respectively. The reaction required the presence of either ascorbic acid or xanthine oxidase. Levels of each catechol increased in proportion to ferric ion concentration and were suppressed by desferrioxamine B methanesulfonate (desferal). Catalase (CAT) inhibited the oxidation by the ascorbate system whereas superoxide dismutase (SOD) had little effect. The addition of hydrogen peroxide to the reaction mixture stimulated the oxidation, but the reaction was not initiated by hydrogen peroxide alone, suggesting that hydrogen peroxide acts as a precursor of hydroxyl radical. SOD and CAT suppressed the demethylenation reactions in the xanthine oxidase system. Hydroxyl radical scavenging agents such as ethanol, benzoate, DMSO, and thiourea effectively inhibited the oxidation by both systems. Urea, which has little effect on hydroxyl radical, was without any effect. These results indicated that hydroxyl radical can effect the cleavage of methylenedioxy group on MDPs.

Primary sequence of duck metallothionein

Only one metallothionein appears in domesticated duck upon zinc induction. The complete amino acid sequence has been elucidated. This metallothionein has the same sequence as the chicken metallothionein, as determined by chemical sequencing of overlapping peptides produced by selective proteinase digestion and confirmed by mass spectrometry. The observation that animals of divergent origins share a common gene product presents an example of extreme conservation of a stress-inducible protein.

[Cloning and sequencing of hemolysin gene from clinical Aeromonas hydrophila]

Aerolysin is one of the important virulence factors for Aeromonas hydrophila infection. To understand the characteristics of the aerolysin gene in clinical A. hydrophila, a genomic library was constructed by using pUC19 as cloning vector. The positive clone containing the aerolysin gene was selected by the colony hybridization method, using the aerolysin probe (an 48 mer oligonucleotide) of aquatic A. hydrophila. Four positive out of 1,200 transformants were obtained from the primarily screened genomic library, and were further identified for specific binding capability by the dot blot hybridization method. One of three positive clones, designated as pAH-1, was further analyzed by the restriction mapping technique. For further sequencing the aerolysin gene nucleotides, the 3.0 kb fragment of A. hydrophila isolated from pAH-1 was cloned into pBluescriptII, pKS+, resulting in plasmid pKAH-1. Subclones of pKAH-1 were constructed and determined for the presence of 48 mer aerolysin gene sequence by dot blot hybridization method. These (subclones pKS+SS and pSK+SS) were selected for nucleotide sequencing by single-stranded dideoxy sequencing method. The nucleotide sequence similarity coefficient between clinical and aquatic strains of A. hydrophila was 76%; whereas between clinical strains of A. hydrophila and A. sobria was 71%. Since the length of the A. hydrophila DNA fragment cloned into pAH-1 is 3.0 kb, a larger size than the aerolysin gene of aquatic A. hydrophila (1.45 kb) and, also, includes 3' region of aerolysin gene in aquatic A. hydrophila, the indication is that the clone, pKAH-1, contains an entire aerolysin gene of A. hydrophila. The similarity between a small region (containing 8 amino acids) of the aerolysin in the clinical A. hydrophila and the alpha toxin of Staphylococcus aureus suggests that there is functional significance in this region.

Maternal transmission of mitochondrial DNA in ducks

Maternal transmission of mitochondrial DNA (mtDNA) has been studied in amphibians, insects and mammals, but little is known about mtDNA inheritance in the ovaripirous avian species. In this study, we have constructed the physical maps of mitochondrial genomes from two different genera of ducks (Cairina and Anas) and taken advantage of the availability of their hybrids to demonstrate that mtDNA is maternally inherited.

Complete homology in metallothionein from two genera of ducks and their hybrids

Metallothionein purified from two genera of domesticated duck, Anas platyrhnchos and Cairina muschata, and their hybrid were analyzed and shown to consist of one identical amino acid sequence. Since most vertebrates carry two or more isospecies of this inducible, thiol rich, metal sequestering protein, this finding suggests that duck metallothionein is evolutionary primitive.

Pigeon metallothionein consists of two species

Two isospecies of metallothionein, a cysteine-rich protein that binds metals, exist in all mammals examined, but only one in some invertebrates and lower animals. Lower vertebrates such as fish and birds have one or two metallothionein genes depending upon the organism. In this study, we show by amino acid sequence determinations that two isospecies of metallothionein, 75% homologous to each other, can be induced by zinc to accumulate in pigeon livers. This is in contrast to single isospecies found in chicken and duck. Each of these two sequences consists of 63 amino acids, with all 20 cysteines in positions held invariant in most if not all class I mammalian metallothioneins. One of these two pigeon isometallothioneins is terminated with histidine at the carboxyl end, which is apparently unique to avians. Its sequence differs from that of duck and chicken by only four substitutions and is the predominant isospecies that accumulates upon induction. The other pigeon metallothionein has lysine at its carboxyl terminus and is devoid of arginine. None of these isospecies carries any aromatic amino acid, which is also characteristic of all higher metallothioneins. As this is the first demonstration with sequence data that two isospecies of metallothionein indeed exist in birds, these results suggest that pigeon metallothionein genes evolved from an ancestral form through duplication and mutation upon specification.

[Determination of protein concentration in human saliva]

Seven colorimetric methods (Biuret, Lowry, a modified Lowry technique using bicinchoninic acid, Coomassie brilliant blue G (CBBG) dye-binding in phosphoric acid, perchloric acid or hydrochloric acid, and bromophenol blue dye-binding) were evaluated for determination of protein concentration in human whole saliva. Using bovine serum albumin (BSA), mucin, and thyroglobulin as protein standards to calculate salivary protein concentration gave different results among the assays used and even with the different standards of the same method. Among the seven methods used, the CBBG dye-binding assay in hydrochloric acid appeared to provide the most accurate estimation of protein concentration in human saliva. Using BSA as a standard, the mean values of human salivary proteins from 39 healthy individuals ranged from 0.72 to 2.45 mg/ml. The optimum conditions for the CBBG dye-binding assay in hydrochloric acid are: (1) the absorbance at 595 nm was measured between 15 to 30 minutes after addition of reagent. (2) the optimum concentration of dye in hydrochloric acid was 0.06-0.12% (w/v) for the assay. (3) the dye reagent was stable within one month.

Metalloforms of metallothionein induced by parenteral copper: the influence of route of administration

Previous results regarding the two metalloforms of MT which accumulate in chick liver following the parenteral administration (ip) of copper were discussed. One metalloform, which is exclusively zinc, was suggested to reflect the marked accumulation of hepatic zinc following copper injection. The present report shows that there is a marked difference in hepatic zinc accumulation if copper is administered iv. Under these conditions there is virtually no change in hepatic zinc and thus MT produced under these conditions appears to contain only copper. We suggest the the changes in zinc metabolism as effected by copper when given intraperitoneally reflect a secondary response analogous to that observed when iron is similarly administered.

Scuba Divers With Disabilities Challenge Medical Protocols and Ethics

Persons with disabilities are scuba diving, as are persons with such conditions as asthma and epilepsy. A recent symposium considered the relevant medical and ethical issues.

Isocratic high-performance liquid chromatographic separation and multiple-wavelength ultraviolet detection of aldicarb and its soil degradation products. Optimization of stationary phase selectivity

The unique selectivities which can be generated through optimization of stationary/mobile phase combinations have been applied to the development of an isocratic, reversed-phase high-performance liquid chromatographic method for the separation of aldicarb and its primary soil degradation products. The method utilizes a cyanopropyl bonded stationary phase and water-acetonitrile mobile phase and is capable of separating aldicarb and its various sulfoxide, sulfone and oxime derivatives in less than 10 min. When combined with multiple-wavelength UV detection and an appropriate preconcentration step, this method can in principle be applied to the routine monitoring of aldicarb and its soil derivatives in water at concentrations less than 1 microgram/l.

Parenteral zinc and tissue metallothionein in normal and diabetic rats

The effect of parenteral zinc on tissue metallothionein (MT) was studied in normal and streptozotocin-induced diabetic rats. The accumulation of Zn-MT in liver and pancreas of normal and diabetic rats following the administration (ip) of various amounts of zinc was not different. Renal Zn-MT was higher in the diabetic group, and this was not changed by zinc injection. Although diabetic rats, relative to normal, possessed a markedly higher concentration of Cu-MT in kidney initially, this difference decreased considerably after zinc injection. The ratio of Cu-MT to cytosolic Cu in kidney was not affected by parenteral zinc and was highest in diabetic rats. Zinc injection markedly reduced food intake, water consumption, and urine output in both normal and diabetic rats. Blood glucose of diabetic rats also decreased 24 h after zinc administration. Our results indicate that relative to normal, MT and zinc metabolism are different in kidney, and to some extent liver, but not different in the pancreas of the chemically induced diabetic rat.

Quantitation of chick tissue zinc-metallothionein by gel electrophoresis and silver stain enhancement

Discontinuous gradient gel electrophoretic systems were developed to quantitate zinc-metallothionein (Zn-MT) in chick tissues, liver and pancreas. Gels were stained with Coomassie Blue initially, then enhanced by silver stain. At least 4 micrograms of Zn-MT could be detected after Coomassie Blue stain, and 1 microgram Zn-MT detected following silver stain enhancement. Significant linearity (correlation coefficient = 0.99) of a standard curve was established in the Coomassie Blue stained gels. The results of our experiment suggest that electrophoretic analysis is a simple and feasible method for the quantitation and identification of Zn-MT in chick tissues.