Contents of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and of 16 further congeners--polychlorinated dibenzodioxins and dibenzofuranes (PCDD/PCDF)--were determined in lipids of adipose tissue and of livers of 3 stillborns and of 17 infants (0.43-44 weeks old) who died from sudden infant death syndrome. International toxic equivalents (I-TEq) calculated for the sum of TCDD together with all of the 16 congeners (1.55-29.63 ng/kg lipids of adipose tissue, n = 20; 2.05-57.73 ng/kg liver lipids, n = 19) were within the range of or lower than the values published for adults. TCDD concentrations in lipids of breast-fed infants were higher (0.38-4.1 ng/kg lipids of adipose tissue, n = 9; 0.49-3.9 ng/kg liver lipids, n = 8) compared to non breast-fed subjects (0.16-0.76 ng/kg lipids of adipose tissue, n = 8; 0.29-0.71 ng/kg liver lipids, n = 7). Neither I-TEq values nor TCDD concentrations exceeded values published for adults. Since even in stillborns PCDD/PCPF were found (I-TEq, 9.70-10.83 ng/kg lipids of adipose tissue, 6.17-8.83 ng/kg liver lipids; TCDD, 1.3-2.1 ng/kg lipids of adipose tissue, 0.76-1.5 ng/kg liver lipids; n = 3), transplacental exposure has to be deduced. All of the findings concerning TCDD concentrations in the organism become intelligible on the basis of a physiological toxicokinetic model which was developed to describe the body burden of TCDD for the entire human lifetime in dependence of TCDD uptake from contaminated nutrition. The model reflects sex and age dependent changes in the following parameters: body weight, volumes of liver, adipose and muscle tissue, food consumption, and excretion of faeces. TCDD is supposed to be taken up orally, to be distributed freely in lipids of the organism and to be eliminated unchanged by excretion in lipids of faeces as well as by metabolism in the liver. The model was used to predict the half-life of elimination of TCDD (4 months in newborns increasing to approximately 5 years in adults) and concentrations of this compound in lipids of adipose tissue, blood, liver and faeces at different ages. Furthermore, the influence of breast-feeding on the TCDD burden of a mother, her milk and her child was simulated. The model was validated by means of own data gained in adipose tissue and livers of infants and also using a series of values measured by other authors in mother's milk and in tissues and faeces of infants and adults. Predictions as well as experimental findings demonstrate a distinct increase in the TCDD body burden of breast-fed infants. Generally, it can be concluded for the excretion of unchanged, non-volatile, non protein bound highly lipophilic compounds that their half-life is short in infants (approximately 5 months) and increases to approximately 10 years reached between 40 and 60 years of age.

No abstract

No abstract

The xyl operator of Bacillus subtilis W23 was identified by deletion analysis of the xyl regulatory region as a 25-base-pair (bp) sequence located 10 bp downstream from the xyl promoter. The outer 10 bp of the xyl operator exhibit perfect palindromic symmetry, while 5 central bp are nonpalindromic. It was demonstrated that the penultimate base pair near the end of this sequence is important for repressor binding. In both strains, expression of xylose-utilizing enzymes appears to be negatively regulated at the level of transcription (5, 6). In B. subtilis 168, a regulatory gene called xy/R has been identified and characterized by complementation (6). We are interested in studying repressor-operator recognition mediating regulation of the xyl operon. In this article, we report the identification by deletion analysis and nucleotide sequencing of the xylR gene and xyl operator from B.subtilis W23 and the first data characterizing a base pair of the xyl operator important for Xyl repressor recognition. MATERIALS AND METHODSBacterial strains and plasmids. The bacterial strains and plasmids used in this study are listed in Table 1. Escherichia coli RRI and HB101 and B. siubtilis 512 and BR151 were generally used for transformations as described previously (1, 2). E. coli RRI was used for transformation with M13 DNA, and E. coli HB101 was used for all other cloning experiments. E. coli JM101 was the host for M13 infection. The culture and growth conditions were as described previously (5). We constructed pWH423 (see Fig. 2) by cloning a 2.2-kilobase-pair BamHI-HindIII DNA fragment from pIWll (21) in pWH331 (5). pWH423ABc/I was constructed from pWH423 by digestion with Bc/1I followed by mung bean nuclease digestion and ligation. DNA sequence analysis revealed that 14 base pairs (bp) (TCATTCTTGATCAA) were missing. pWH419 contains the 100-bp xy/ promoteroperator SspI-NsiI fragment from pWH416 (5) in the EcoRV-PstI site of pWH341. pWH341 was constructed by inserting the polylinker from pIC20R (10) EcoRV and HindIII sites of pWH341. The deletion plasmids were constructed by digesting pWH419 with BamHI followed by BAL 31 as previously described (9), ligating either an EcoRI linker (pWH429 and pWH430) or a Sall linker (pWH428 and pWH432) to the ends, transforming E. coli HB101, preparing the bulk of plasmid DNA, digesting it with EcoRI or EcoRI and Sa/I, separating the products on a 5% polyacrylamide gel, eluting fragments of the desired length from the gel, and recloning them into the respective sites of pWH331 (pWH428 and pWH432) or pWH341 (pWH429 and pWH430). pWH439, pWH440, and pWH441 contain the respective deletions from the EcoRI site with the HindlIl linker CAAGCTTG recloned into pWH331. All deletions were verified by sequencing.General methods. Preparation of plasmid DNA from E. coli (7,8) and B. subtilis (16) and elution of DNA from polyacrylamide gels (11) were done as described before. All of the other general methods used, including BAL 31 and mung bean nuclease digestions, were done as already described (9).Enzym...

Kinetics of the metabolism of 1,2-epoxybutene-3 (butadiene monoxide) were investigated in liver fractions of mouse, rat, and man. In these species similar enzyme characteristics were found. In microsomes, no NADPH-dependent metabolism of butadiene monoxide was detectable. Epoxide hydrolase activity was found only in microsomes. The Vmax [nmol butadiene monoxide/(mg protein x min)] was 19 in mouse, 17 in rat, and 14 in man and the apparent Km (mmol butadiene monoxide/l incubate) was 1.5 in mouse. 0.7 in rat, and 0.5 in man. Glutathione S-transferase activity was found in cytosol only, revealing first order kinetics in the measured range. The ratio Vmax/Km [(nmol butadiene monoxide x 1)/(mg protein x min x mmol of butadiene monoxide)] was 15 in mouse, 11 in rat, and 8 in man. The data obtained were used to extrapolate on the total rate of butadiene monoxide metabolism for each species in vivo: it was calculated to be 1.3 times higher in mice and 2.3 times lower in man compared to rats, when corrected for body weight.