Characterization of the pUC19-lacZC141 reversion system for assaying chemical mutagenesis.

pUC19-lacZC141 DNA contains a proline codon at positions 141 to 143, where an alanine codon normally appears in the original lacZ gene. pUC19-lacZC141 DNA was produced using site-directed mutagenesis. After transfection of pUC19-lacZC141 DNA into lacZ hosts, the transformants produce white colonies on an agar plate containing X-gal and IPTG. lacZ+ revertants can be identified by their dark- and light-blue colony color against a background of non-mutant white colonies, indicating restoration of beta-galactosidase activity. N-Methyl-N'-nitro-N-nitrosoguanidine (MNNG) and methylmethanesulfonate (MMS) were used to characterize the pUC19-lacZC141 DNA reversion assay. Mutagenesis resulting from methylated DNA was examined in Escherichia coli strains JM109, BMH71-18mutS, and SURE, which differ in their repair systems for DNA damage. In JM109 and BMH71-18mutS, mostly G:C-->A:T transitions and some G:C-->C:G or G:C-->T:A transversions were observed. E. coli SURE produced, in addition, frameshift mutations (approximately 10%). The DNA sequence analysis of 174 induced mutants indicated that the major effect of methylation is on single base-pair substitutions with a slight effect on deletion frameshifts. All mutations are consistent with miscoding of guanine or cytosine adducts or lesions. Transitions account for 158 of 165 (96%) induced base substitutions. Approximately 93% of the base-substitution mutations occurred at the expected positions 141 to 143 in the lacZ gene. The pUC19-lacZC141 assay was sufficiently sensitive to allow the detection of mutations in lacZ- hosts with different repair mechanisms. The pUC19-lacZC141 DNA reversion system will permit the assaying of other chemicals not otherwise amenable to mutagenesis studies.

Acute toxicity, percutaneous absorption and effects on hepatic mixed function oxidase activities of 2,4,4'-trichloro-2'-hydroxydiphenyl ether (Irgasan DP300) and its chlorinated derivatives.

Acute toxicity of 2,4,4'-trichloro-2'-hydroxydiphenyl ether (Irgasan DP300) (I) and its three chlorinated derivatives, 2',3,4,4'-tetrachloro-2-hydroxydiphenyl ether (II), 2',4,4',5-tetrachloro-2-hydroxydiphenyl ether (III) and 2',3,4,4',5-pentachloro-2-hydroxydiphenyl ether (IV), in mice were examined by intraperitoneal injection. The LD50 values of Irgasan DP300, II, III and IV were 1,090, 710, 650 and 430 mg/kg, respectively. The percutaneous absorptions of these tritiated compounds were also examined by the application on the backs of mice. The radioactivities in most tissues reached to the maximal levels at 12 h or 18 h after dosing, which corresponded to 11-76% of the maximal levels given by the oral administration (Kanetoshi et al. 1988a). These results show the high percutaneous absorbability of Irgasan DP300 and its chlorinated derivatives. The intraperitoneal administrations of III and IV to rats induced hepatic microsomal aminopyrine N-demethylase and aniline 4-hydroxylase activities similarly to phenobarbital. These chlorinated derivatives also increased cytochrome P-450 content, and the activities of aminopyrine N-demethylase and N-methylaniline N-demethylase in hepatic microsomes from mice. The extents of the increases were similar to those by phenobarbital and 3-methylcholanthrene.

Formation of polychlorinated dibenzo-p-dioxins upon combustion of commercial textile products containing 2,4,4'-trichloro-2'-hydroxydiphenyl ether (Irgasan DP300).

Commercial textile products containing 2,4,4'-trichloro-2'-hydroxydiphenyl ether (Irgasan DP300) as an antimicrobial agent gave dichlorodibenzo-p-dioxin(s) (di-CDD) upon combustion. The extent of conversion of Irgasan DP300 into di-CDD(s) reached 19-43% at 600 degrees C. Upon bleaching the textile products with sodium hypochlorite, Irgasan DP300 was chlorinated to 2',3,4,4'-tetrachloro-2-hydroxydiphenyl ether, 2',4,4',5-tetrachloro-2-hydroxydiphenyl ether and 2',3,4,4',5-pentachloro-2-hydroxydiphenyl ether. These chlorinated derivatives were converted into trichlorodibenzo-p-dioxins and tetrachlorodibenzo-p-dioxin upon combustion, which are more toxic than di-CDD(s). These results suggest that the bleaching and incineration of textile products containing Irgasan DP300 result in environmental pollution by PCDDs.

Chlorination of Irgasan DP300 and formation of dioxins from its chlorinated derivatives.

Irgasan DP300 (2,4,4'-trichloro-2'-hydroxydiphenyl ether) (I), an antimicrobial agent for use with fabrics, was easily chlorinated with sodium hypochlorite to give 2',3,4,4'-tetrachloro-2-hydroxydiphenyl ether (II), 2',4,4',5-tetrachloro-2-hydroxydiphenyl ether (III) and 2',3,4,4',5-pentachloro-2-hydroxydiphenyl ether (IV). Irgasan DP300 and its chlorinated derivatives were readily converted into polychlorinated dibenzo-p-dioxins (PCDDs) by heating: Irgasan DP300 was converted into dichlorodibenzo-p-dioxin(s) (di-CDD, 42%); II into two trichlorodibenzo-p-dioxins (tri-CDDs, 22%) and three tetrachlorodibenzo-p-dioxins (tetra-CDDs, 46%); III into two tri-CDDs (44%), more than two tetra-CDDs (25%) and pentachlorodibenzo-p-dioxin(s) (penta-CDD, 1%); and IV into two tetra-CDDs (16%), trace amounts of penta-CDD(s) and four hexachlorodibenzo-p-dioxins (hexa-CDDs, 40%). Although UV irradiation of Irgasan DP300, II and III gave PCDDs, the amounts of PCDDs formed were much smaller than those obtained by heating. Moreover, PCDD was not detected in the UV irradiation of IV. The identified products suggested that disproportionation of chlorine atom(s) occurred in the photolysis.

Chromatium sulfite reductase. I. Characterization of thiosulfate-forming activity at the cell extract level.

Thiosulfate and sulfide were detected in the sulfite reductase reaction catalyzed by a cell-free extract of photoautotrophically grown Chromatium vinosum. Hydrogen was consumed upon addition of sulfite to the extract in the presence of hydrogenase and methylviologen. Hydrogen uptake proceeded biphasically. During the first phase, thiosulfate and sulfide were formed concomitant with the decrease in sulfite. After the disappearance of sulfite, hydrogen was consumed with reduced velocity and sulfide accumulated as the final product with the total consumption of three mol of hydrogen per mol of sulfite. The molecular weight of a major sulfite reductase was estimated to be about 180,000 by the polyacrylamide disc electrophoresis method using enzyme staining. Arsenite. EDTA, alpha,alpha'-dipyridyl, cyanide, or azide did not inhibit the activity at the concentration of 1 mM. The activity was present in the soluble fraction and was stable at --20 degrees C.

Thiamine triphosphatase activity of myosin and accelerating effect of thiamine di- and tri-phosphates on superprecipitation of actomyosin.

TTP accelerated ATP-induced superprecipitation of actomyosin in as low a concentration as 30 muM and decreased light scattering by actomyosin. These effects could also be observed in the same way, but to a lesser degree, by addition to TDP. Myosin was able to hydrolyze TTP to TDP, but some important differences were confirmed between myosin TTPase and ATPase. Myosin TTPase was inhibited by actin and showed a much larger Km than that of ATPase. TTP significantly inhibited myosin B ATPase and ATP greatly inhibited myosin B TTPase. These findings suggest that the accelerating effect of TDP and TTP may be due to the binding of thiamine phosphate to the regulatory site of myosin followed by a change in its physical chemical property, rather than due to the competitive binding of thiamine phosphate to the catalytically activity site of myosin.