Biochemical studies on strain differences of mice in the susceptibility to nitrogen dioxide

Strain differences of mice in their susceptibility to nitrogen dioxide (NO₂) were examined by measuring the activities of antioxidative protective enzymes, and the amounts of antioxidants and lipid peroxides in lungs. Four strains of mice: ICR, BALB/c, ddy and C57BL/6 were used in this study and their LC₅₀ values after exposure to NO₂ for 16 hr were: 38, 49, 51 and 64 ppm, respectively (1).Genetic strain differences were observed in the enzyme activities, the antioxidant contents and lipid peroxide contents among these four different strains. The activities of glutathione peroxidase (GP_x), glutathione S-transferase, and superoxide dismutase (SOD), and the contents of non-protein sulfhydryls (NPSH), α-tocopherol (α-Toc) and total lipids in lungs of the four strains were related to their LC₅₀, while TBA reactants in lungs of the four strains were inversely related to their LC₅₀.After exposure to 20 ppm NO₂ for 16 hr, the activities of the protective enzymes and the contents of NPSH decreased, while the level of α-Toc increased markedly. The activities of GP_x, 6-phosphogluconate dehydrogenase, SOD and disulfide reductase, and the contents of NPSH, α-Toc and total lipids were also related to their LC₅₀. On the other hand, TBA reactants increased higher than those of the control groups and were inversely related to their LC₅₀.These results suggest that the protective enzymes and the antioxidants are important factors as defence mechanism in lungs to NO₂ and that the intensity of the protective systems in pigmented strains is generally greater than that in albino strains.     

Degradation of methylmercury by selenium

When methylmercury was incubated in the presence of selenite and reduced glutathione (GSH), the mercury which was extracted into benzene under acidic condition decreased gradually with the elapse of time. This decrease was due to the cleavage of mercury-carbon bond of methylmercury. The reaction did not proceed when selenite or GSH was singly added to the reaction mixture. L-Cysteine, 2-mercaptoethanol and sodium sulfide in place of GSH also were effective for decomposition of methylmercury in combination with selenite, but oxidized glutathione (GSSG) and L-cystine were not. This suggests that reduction of selenite is needed for the degradation of methylmercury. Thus, the effect of reduced metabolites of selenite produced by GSH was investigated. Glutathione selenotrisulfide (GSSeSG) requierd GSH for the degradation of methylmercury, whereas H₂Se possessed a strong activity even in the absence of GSH. This may indicate that H₂Se is involved directly in the conversion of methylmercury to inorganic mercury. This phenomenon found in $\text{in vitro}$ experiments is discussed in relation to the biotransformation of methylmercury.     

Persistence of genomes of both herpesvirus of turkeys and Marek's disease virus in a chicken T-lymphoblastoid cell line

A cell line tentatively designated as MDCC-BO1(T), was established from spleen cells of an apparently healthy chicken inoculated with herpesvirus of turkey (HVT). BO1(T) cells were T lymphoblastoid cells and the more than 95% of them had Marek's disease (MD) tumor-associated surface antigen (MATSA). However, no viral internal antigens or membrane antigens could be demonstrated in them by immunofluorescence tests using chicken anti-HVT and -MD virus (MDV) sera. The virus could be rescued from BO1(T) cells by co-cultivation with chick embryo fibroblasts (CEF). The DNA of the rescued virus was characterized as HVT DNA by its sedimentation profile in a neutral glycerol gradient and its endonuclease Hind III cleavage-pattern. Ultrastructural studies on CEF infected with the rescued virus revealed the presence of HVT-like virions. However, DNA-DNA reassociation kinetics showed that the BO1(T) cells contained a few copies of NVT and also MDV genomes.     

Further morphological characterization and structural proteins of infectious bursal disease virus.

An outer layer surrounding the capsid of infectious bursal disease virus was evident from electron micrographs of intact virus particles having diameters of 62 to 63 nm. The capsid was found to be composed of large morphological units or capsomeres, measuring about 12 nm in diameter. The architecture of the capsid appears to be that of T = 3 symmetry, with a probable 32 morphological units by rotational enhancement of image detail. Structural proteins of infectious bursal disease virus consist of seven species, two major and five minor polypeptides. These are P1 to P7, with molecular weights of 133 x 10(3), 124 x 10(3), 98 x 10(3), 51 x 10(3), 33 x 10(3), 26 x 10(3), and 23 x 10(3), respectively.     

Dose-response relations for dicentric yields in G0 lymphocytes on man and crab-eating monkey following acute and chronic γ-irradiations

A comparison has been made of dicentric yields in G₀ lymphocytes between man and crab-eating monkey, Macaca fascicularis, after acute and chronic γ-irradiations. With acute irradiation (49.6 rad/min) there was no significant difference between them, but for the chronic irradiation (17.1 rad/h) a significant difference was observed between the species. When the dose-response relations were fitted to the linear-quadratic model (Y = αD + βD²), the species-difference observed for chronic irradiation was almost entirely due to change in the value of β. In addition, after chronic irradiation the β-value for monkey was almost negligible, but that for man was significant. Post-irradiation incubation experiment showed that cells with dicentrics were partly eliminated during the course of chronic irradiation, because there were appreciable reductions of dicentric yields (ca. 25% for both man and monkey at 400 rad) together with mitotic indices (ca. 30% and 60% for man and monkey, respectively, at 400 rad). Accordingly, it would be reasonable to postulate that G₀ repair for dicentrics other than selection mechanism must play a major role in the effects of low dose rate. It can be further suggested that G₀-repair capacity for chromosal damages leading to dicentrics may be different among different primate species.     

Dicentric yields induced by gamma-radiation and chromosome arm number in primates.

To evaluate the effect of the chromosome arm number on the yield of dicentric chromosomes, frequencies of gamma-ray-induced chromosome aberrations were examined with peripheral lymphocytes from three different primate species, Saimiri sciureus (arm number, 77), Macaca fascicularis (arm number, 83) and Nycticebus coucang (arm number, 99). Irradiated blood samples were cultured by the same standard technique as that commonly used for human lymphocytes. The yields of dicentrics and dicentrics plus rings at doses of 100, 200 and 300 rad of gamma-irradiation were not significantly different among the three species, in spite of the difference in the chromosome arm number. Furthermore, dose-response relationships for these species were consistent with that for man. Statistical analysis indicated that the expected dicentric yields calculated from the arm number model were significantly different from the observed yields at 200 and 300 rad doses (P less than 0.01). From these results it can be pointed out that there is no correlation between the yield of dicentrics and the effective chromosome arm number, and that the chromosomal radiosensitivity of these primates is essentially the same as that of man, at least in the lymphocyte system.     

Regional replication of the bacterial chromosome induced by derepression of prophage lambda

Summary Derepression of prophage in E. coli strain K12 results in constitutive synthesis of the enzymes directed by the nearby bacterial operon, gal (escape synthesis). Phage 82 fails to cause escape synthesis despite that it lysogenizes the strain K12 at the site identical to that of on the host chromosome. The reason for the observed difference between 82 and is studied in the light of the recent finding that escape synthesis in -lysogen is closely associated to phage-promoted replication of bacterial chromosome contiguous to the prophage including gal operon (escape replication). Excision-defective mutants from 82, 82int or 82xis, do initiate escape synthesis, suggesting that the prophage 82 is normally excised too quickly after induction to allow sufficient escape replication. In support of this, much more DNA hybridizable to bacterial DNA contained in gal accumulates after induction of 82int than after induction of 82. Studies with various hybrid phages between 82 and have suggested: 1. The occurrence of gal escape synthesis depends on the nature of the region between b2 and N in the map. 2. Regions of the 82 genome on both sides of the attachment site contribute independently to prevent gal escape synthesis. Implications of these results are discussed with regard to the factors involved in the prophage excision.The IIIrd article of this series is in Molec. Gen. Genet. 159, 185–190 (1978)     

Biosynthetic mechanism of ribulose-1,5-bisphosphate carboxylase in the purple photosynthetic bacterium,Chromatium vinosum: II. Biosynthesis of constituent subunits

[³⁵S]Methionine-labeled free subunits A and B of RuBP carboxylase were present in barely detectable amounts; the radioactivity in the free subunit B was approximately 1/150th of that in the subunit B contained in the holoenzyme of RuBP carboxylase. The turnover rates of subunits A and B in the holoenzyme were equal at each time during the incubation period. The ratio of subunit A to subunit B was constant throughout the incubation time both in quantity and in the level of [³H]leucine and [³⁵S]methionine incorporated. CO₂ contained in the incubation medium suppressed [³⁵S]methionine incorporation into both subunits A and B equally. These results suggest that the biosynthesis of subunits A and B is completely synchronized and may be regulated by identical mechanisms.     

Cyclin B in fish oocytes: its cDNA and amino acid sequences, appearance during maturation, and induction of p34cdc2 activation.

Under the influence of maturation-inducing hormone (MIH) secreted from follicle cells, oocyte maturation is finally triggered by maturation-promoting factor (MPF), which consists of a homolog of the cdc2+ gene product of fission yeast (p34cdc2) and cyclin B. Two species of cyclin B clones were isolated from a cDNA library constructed from mature goldfish oocytes. Sequence comparisons revealed that these two clones are highly homologous (95%) and were found to be similar to Xenopus cyclin B1. Using monoclonal antibodies against Escherichia coli-produced goldfish cyclin B and the PSTAIR sequence of p34cdc2, we examined the levels of cyclin B and p34cdc2 proteins during goldfish oocyte maturation induced in vitro by 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (17 alpha, 20 beta-DP), a natural MIH in fish. Protein p34cdc2 was found in immature oocyte extracts and did not remarkably change during oocyte maturation. Cyclin B was not detected in immature oocyte extracts and appeared when oocytes underwent germinal vesicle breakdown. Cyclin B that appeared during oocyte maturation was labelled with [35S]methionine, indicating its de novo synthesis. Introduction of E. coli-produced cyclin B into immature oocyte extracts induced p34cdc2 (MPF) activation. Although the possibility that immature goldfish oocytes contain an insoluble cyclin B is not completely excluded, these results strongly suggest that 17 alpha, 20 beta-DP induces oocytes to synthesize cyclin B, which in turn activates preexisting p34cdc2, forming active MPF.     

A three-dimensional computerized reconstruction of the rectum, anus and surrounding muscles of the rat fetus at the 20th gestation day

Using fetuses of Wistar/I rats on the 20th gestation day. We designed a three-dimensional computerized reconstruction of the rectum, anus and the surrounding muscles. The tissues were fixed in Bouin's solution sagittally sectioned serially were stained with hematoxylin-eosin. Light microscopic pictures at 40 x magnification were subjected to the analysis using a three-dimensional image processing system, consisting of a drum-scanner, a general purpose computer (Micro VAX II), and a color image processor. The results showed that this system clearly reconstructed the three-dimensional image of the rectum, anus and the surrounding muscles and suggested the presence of the puborectal muscle sling.