Activation of the food mutagens IQ and MeIQ by hepatic S9 fractions derived from various species

The ability of hepatic S9 mixes derived from different rodent species (rat, mouse, Syrian and Chinese hamster) to activate the mutagens 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) was investigated using Salmonella typhimurium strain TA98. In general, the mutagenicity of IQ and MeIQ was greatest in the presence of S9 fractions from Swiss albino mice and least from fractions derived from Chinese hamsters. However, treatment of rats or hamsters with Aroclor 1254 had little or no effect on the activation of IQ or MeIQ to mutagens.     

Iron-sulfur cluster in aconitase. Crystallographic evidence for a three-iron center

Native x-ray diffraction data from single crystals of inactive aconitase from pig heart (Mr 80,000) have been collected on oscillation films to 2.7 A. Analysis shows that significant measurements of the anomalous scattering signal from the Fe-S cluster in the enzyme are available in the film data. The 5.0-A resolution anomalous difference Patterson function contains vectors for one Fe-S cluster (one aconitase molecule) per asymmetric unit in space group P2(1)2(1)2 with a = 173.6, b = 72.0, and c = 72.7 A. At 2.7-A resolution, the vector map is best interpreted by three Fe sites separated from each other by less than 3 A. The single-crystal diffraction data thus confirm the presence of a 3Fe center in the inactive form of aconitase. Furthermore, the data provide crystallographic evidence that 3Fe clusters exhibit structural heterogeneity. The Fe-Fe vectors cannot be interpreted in terms of 4-A distances as observed for the [3Fe-3S] cluster in Azotobacter ferrodoxin (Ghosh, D., O'Donnell, S., Furey, W., Robbins, A. H., and Stout, C. D. (1982) J. Mol. Biol. 158, 73-109). The results are therefore in agreement with a [3Fe-4S] cluster having 2.7-A Fe-Fe distances (Beinert, H., Emptage, M. H., Dreyer, J.-L., Scott, R. A., Hahn, J. E., Hodgson, K. O., and Thomson, A. J. (1983) Proc. Natl. Acad. Sci. U. S. A. 80, 393-396). However, the data do not unambiguously discriminate between this model and other 3Fe clusters having short Fe-Fe distances.     

Distributions of cell populations within alpha-particle range of plutonium deposits in the rat and beagle testis

Plutonium is not uniformly distributed in testicular tissues; thus some cell populations may receive larger or smaller radiation exposures than would be expected if the nuclide were uniformly distributed. The distributions of cell populations within alpha-particle range of Pu deposits in rat and beagle testes were determined. The data were collected from autoradiographs of testicular tissues containing 241Pu. A cell distribution factor (CDF) was determined for each cell population and is defined as the average number of each cell type within alpha-particle range of each observed Pu deposit relative to the number of each cell type that would be expected within alpha-particle range of each Pu deposit, if the deposits were distributed uniformly. In addition, the percentage of the spermatogonial stem cell population within alpha-particle range of Pu deposits was determined. In rats, the CDF for the spermatogonial stem cells is about 2.2. This value is similar to other enhancement and inhomogeneity factors reported for rodents in the literature. In beagles the CDFs to all cells in the seminiferous epithelium were less than the rats. In addition, the percentage of spermatogonial cells within alpha-particle range of Pu concentrations in the interstitial tissues was a factor of about 3 less in the dog than in the rat. The largest CDFs seen in both species were in the interstitial tissues, particularly for Leydig cells. Because the organization of testicular tissues in the beagle is quite different from rodents but more similar to human, the results from this study suggest that extrapolations from rodents to humans may tend to overestimate the potential for radiation exposure to spermatogonial stem cells as well as the fraction of the spermatogonial stem cell population at risk to exposure from internally deposited 239Pu.     

Roles of the trkB and trkC gene products of Escherichia coli in K+ transport

Mutations at the trkB and trkC loci of Escherichia coli produce an abnormal efflux of K+. The mutations are partially dominant in diploids and revert frequently by what appears to be intragenic suppression to the null state. The mutations can be reverted by insertion of Tn10 into the mutated gene, and spontaneous revertants are fully recessive to the mutant allele in diploids. K+ efflux produced by NEM* and by DNP* persists in strains with presumed null mutations at either locus, indicating neither gene product is the primary target for the effect of these inhibitors on K+ efflux. The results are consistent with the view that trkB and trkC encode independent systems for K+ efflux. Mutations at these loci alter regulation of the process so that K+ efflux occurs inappropriately. A second mutation to the null state abolishes this abnormal K+ efflux. These genes may encode K+/H+ antiporters, an activity postulated to mediate K+ efflux and demonstrated to exist in E. coli and other bacteria.     

Antitumor properties of vindesine-monoclonal antibody conjugates

Summary The anticancer alkaloid vindesine (VDS) was conjugated to four mouse monoclonal antibodies recognizing human tumor-associated antigens. The antibodies were 96.5 (antimelanoma, IgG2a); 791T/36 (antiosteogenic sarcoma, IgG2b); 11.285.14, and 14.95.55 (anticarcinoembryonic antigen, IgG1 and IgG2a respectively). Conjugates VDS-96.5 and VDS-791T/36 were tested in vitro and shown to be specifically cytotoxic for target cells expressing the appropriate antigen. The in vivo effects of the antibodies and conjugates were tested against human tumor xenografts in athymic or immunodeprived mice using multiple treatments. Conjugate VDS-96.5 retarded the initial growth of a melanoma xenograft, whereas free antibody was without effect. Similarly, VDS-791T/36 but not free antibody retarded the growth of osteogenic sarcoma 791T. The most marked antitumor effects observed were those obtained with VDS conjugates of the anti-CEA antibodies against a colorectal tumor xenograft. Antibody 14.95.55 suppressed tumor growth both alone and as a VDS conjugate, whereas 11.285.14 produced only a slight effect alone but an almost complete and lasting suppression of tumor growth as a VDS conjugate. Free VDS had little effect at nontoxic levels. Acute studies showed that VDS-11.285.14 conjugate was considerably less toxic than free VDS in Balb/c mice.     

Exposure of E. coli to nitrosocimetidine induces the adaptive response to alkylating agents

The cytotoxic and mutagenic properties of nitrosocimetidine (NC), together with its ability to induce the adaptive response DNA-repair pathway were compared with those of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) using Escherichia coli as test organism. MNNG was found to be 250-fold more cytotoxic and 500-fold more mutagenic than NC. Prior cultivation of E. coli in low concentrations of NC protected it against the cytotoxic and/or mutagenic effects of challenge with either NC or MNNG or methyl methanesulphonate (MMS). Induction of the adaptive response by prior cultivation in low concentrations of MNNG reduced the mutagenic and cytotoxic effects of subsequent NC challenge. These results lead us to conclude that although NC is a less potent mutagen than MNNG, the DNA lesions it produces are capable of not only inducing, but also of being repaired by, the adaptive response.     

Disc Plate Method of Microbiological Antibiotic Assay: I. Factors Influencing Variability and Error 1

Several factors are investigated that normally cause variation in zone diameters in conventional disc plate diffusion assay procedures. Of these factors the most serious is the unequal exposure of the individual plates at top or bottom of stacks to temperatures above and below room temperature. This unequal temperature exposure is avoided by novel handling and incubation procedures. A major variable, but one which can be controlled, is the varying time interval between pouring seeded agar and the time of applying the pads with antibiotic to the plates. This influence of time of setting and the effects of several other sequential operations are combined into a composite variable. This variable is then accounted for and normalized by interposing "external" reference plates set with a reference solution in the sequence of approximately 100 plates. No "internal" reference zones are employed. Such factors as volume of agar poured, wedge shape of agar in a dish, volumetric errors in dilutions, and timing considerations are studied and discussed. The results of this study form the basis for a test protocol which is presented in a following paper.     

Effects of Dose on the Induction of Dominant-Lethal Mutations and Heritable Translocations with Ethyl Methanesulfonate in Male Mice

Genetic damage by ethyl methanesulfonate (EMS) in male mice was measured at doses ranging from 50 to 300 mg/kg with dominant-lethal mutations and reciprocal translocations as endpoints. No appreciable increase in dominant-lethal mutations was detected following a dose of 100 mg/kg. Dominant lethals induced by EMS were convincingly detected only after a dose of 150 mg/kg, but in the translocation experiment an increase in the genetic effect was detectable at the 50 mg/kg dose. It is likely that dominant lethals had also been induced at the 50 and 100 mg/kg doses, but were not detected due to the relative insensitivity of the dominant..lethal procedure. Thus, for detection of low levels of EMS-induced chromosome breakage, translocations are a much more reliable endpoint than are dominant-lethal mutations. A procedure for large-scale screening of induced translocations is described.—The dominant-lethal dose-response curve, plotted on the basis of living embryos as a percentage of the control value, is clearly not linear as it is markedly concave downward. Similarly, the translocation dose-response curve showed a more rapid increase in the number of translocations with dose than would be expected on the basis of dose-square kinetics. It is clear for both of these endpoints that the effectiveness of EMS in inducing chromosome breakage is proportionately much lower at low doses.