The usefulness of the micronucleus assay for investigating the radiation response of hepatocytes was examined. The frequency was defined as the ratio of the total number of micronuclei to the number of hepatocytes examined. The dose-response curves were curvilinear after X rays and linear after neutrons. These dose-response curves were analyzed by a linear-quadratic model, frequency = aD + bD2 + c. The a/b ratio was 3.03 +/- 1.26 Gy following X irradiation. This value is within the range of the alpha/beta ratios reported by others using the clonogenic assay of hepatocytes. While the a/b value for neutrons was 24.3 +/- 11.7 Gy, the maximum relative biological effectiveness of neutrons was 6.30 +/- 2.53. Since the micronucleus assay is simple and rapid, it may be a good tool for evaluating the radiation response of hepatocytes in vivo. 相似文献
Summary For the production of a herbicide, 5-amino-levulinic acid (ALA), from anaerobic digestion liquor, the utilization of the photosynthetic bacterium, Rhodobacter sphaeroides was examined. This bacterium could produce ALA extracelularly from this liquor with the addition of levulinic acid (LA), an inhibitor of ALA dehydratase (ALAD), and glycine, a precursor of ALA biosynthesis in the Shemin pathway. Succinate (another precursor) addition was unnecessary for ALA production. When repeated additions of LA were made together with glycine ALA production was significantly enhanced. However, above three additions of LA, ALA production was not further enhanced. The maximum value of ALA production attained was 4.2 mM (0.63 g/ 1), which was over double that of other ALA producers such as Chlorella vulgaris. Propionic acid was predominantly utilized compared with other lower fatty acids, suggesting that this might be converted to ALA via succinyl-coenzyme A (CoA) in the methylmalonyl-CoA pathway.Offprint requests to: Y. Nishizawa 相似文献
Changes in foliage density distribution with altitude and its effect on shoot growth and flowering were studied in forest section planes (profiles) of subalpine forests and scrubs (Krummholz) in Nepal and Japan.Patterns of foliage in forest canopy were evaluated by an analysis of variance. Foliage densities were very high at high altitude canopies, but the change in spatial patterns along altitude differs in both areas.The spatial pattern of new shoot production was similar to that of current foliage density and was affected by the amount of foliage above the sample probably through light condition. Flowering of tall trees occurred in the surface of the upper canopy, but a shrub species flowered even under tree canopies. 相似文献
NfsB is an oxygen-insensitive nitroreductase of Escherichia coli with significant amino acid sequence homology to the major flavin reductase (FRase I) of Vibrio fischeri. Here, we show that NfsB is convertible to an FRase I-like flavin reductase three times as active as the authentic FRase I by a single amino acid substitution in the least-conserved region. 相似文献
Persistent infections with mumps virus were established in several human lymphoid cells of T-cell origin (Molt-4, TALL-1, and CCRF-CEM) and human monocyte cells (U937 and THP-1). 2′,5′-Oligoadenylate synthetase (2–5AS) activity was demonstrated to be only slightly induced by interferon (IFN) or TPA (12-O-tetradecanoyl-phorbol-13-acetate) treatment in these cells. Treatment of the persistently infected cells with IFN or TPA did not stimulate an increase in the amount of synthetase mRNA. Induction of cell differentiation and augmentation of IFN production by TPA were demonstrated in U937 cells persistently infected with mumps virus (U937-MP). Similar results for IFN production were obtained from differentiated U937 cells. It is suggested that cell differentiation of U937 cells might be associated with the development of IFN inducibility. 相似文献
Interactions of externally added plastoquinone (PQ) derivatives(PQ0-PQ3) with the photosystem II (PSII) acceptor side wereinvestigated in PSII membrane fragments prepared from spinachby measuring the photoreduction rates of PQ derivatives at variousPQ concentrations, and the following results were obtained. From the kinetic analysis, all the PQ derivatives (PQ0-PQ3)except PQ3 were shown to accept electrons at two sites (theQB site and the PQ site) as in the case of Synechococcus vulcanusPSII particles with benzoquinone derivatives [Satoh et al. (1995)Plant Cell Physiol. 36: 597]. Affinities of PQ derivatives at the QB site increased as thelength of the isoprene side chain got longer, while those atthe PQ site were not very much different for all the PQ derivativestested in this study. The inhibitory effect of DCMU was noncompetitive, and, therefore,the affinity of PQ3 for the PQ site was determined while thatfor the QB site could not be estimated presumably due to itsfairly high affinity to the site. Based on the results obtained using PQ derivatives, the mechanismof interaction of an authentic PQ, PQ9, at the QB site is discussed. (Received May 2, 1996; Accepted July 24, 1996) 相似文献
Interleukin 3 (IL-3) or granulocyte macrophage colony-stimulating factor (GM-CSF) activates c-fos, c-jun, and c-myc genes and proliferation in both hematopoietic and nonhematopoietic cells. Using a series of deletion mutants of the beta subunit of human GM-CSF receptor (hGMR) and inhibitors of tyrosine kinase, two distinct signaling pathways, one for activation of c-fos and c-jun genes, and the other for cell proliferation and activation of c-myc gene have been elucidated. In contrast to wealth of information on the pathway leading to activation of c-fos/c-jun genes, knowledge of the latter is scanty. To clarify the mechanisms of activation of c-myc gene by cytokines, we established a transient transfection assay in mouse proB cell line BA/F3 cells expressing hGMR. Analyses of hGMR beta subunit mutants revealed two cytoplasmic regions involved in activation of the c-myc promoter, one is essential and the other is dispensable but enhances the activity. These regions are located at the membrane proximal and the distal regions covering amino acid positions 455-544 and 544-589, respectively. Characterization of cis-acting regulatory elements of the c-myc gene showed that the region containing the P2 promoter initiation site is sufficient to mediate the response to mIL-3 or hGM-CSF. Electrophoretic mobility shift assay using an oligonucleotide corresponding to the distal putative E2F binding site revealed that p107/E2F complex, the negative regulator of E2F, decreased, and free E2F increased after mIL-3 stimulation. These results support the thesis that mIL-3 or hGM-CSF regulates the c-myc promoter by altering composition of the E2F complexes at E2F binding site. 相似文献
A synthetic 22-mer oligodeoxyribonucleotide having an AACGTT palindrome, AAC-22, induced interferon (IFN) production and augmented the natural killer (NK) activity in murine splenocytes, whereas its analogue, ACC-22, having an ACCGGT palindrome, did not. The binding of AAC-22 to splenocytes was not different from that of ACC-22. Lipofection of AAC-22 to splenocytes remarkably enhanced IFN production and NK cell activity, whereas that of ACC-22 caused little enhancement. These results strongly suggest that the prerequisite for IFN production is not the binding of AAC-22 to the cell surface receptors, but its penetration into the spleen cells. 相似文献
A specific-locus test was carried out to examine the mutagenic activity of N-ethyl-N-nitrosourea (ENU) on mouse primordial germ cells (PGC). Embryos of C3H/He mice were treated transplacentally with 30 or 50 mg ENU per kg of maternal body weight on day 8.5, 10.5, or 13.5 of gestation (G8.5 day, G10.5 day, or G13.5 day). Male and female mice that had been treated with ENU in embryonic stages were mated with female or male tester PW mice to detect recessive mutations induced in PGC.
ENU induced recessive mutations at a relatively high rate in PGC at these developmental stages. The most sensitive stage was G10.5 day. On G8.5 day, the induced mutation rate in males and females was not significantly different. Cluster mutations, which originate from the limited number of PGC and cell killing, were more frequently induced at an earlier developmental stage. The induced mutation rate per unit dose of ENU (1 mg/kg) was higher in G8.5 and G10.5 day PGC than in stem-cell spermatogonia. It can be concluded that mouse PGC are more sensitive than stem-cell spermatogonia to the induction of recessive mutations by ENU. 相似文献