Correlation between depression of catabolite control of xylose metabolism and a defect in the phosphoenolpyruvate:mannose phosphotransferase system in Pediococcus halophilus.

Pediococcus halophilus X-160 which lacks catabolite control by glucose was isolated from nature (soy moromi mash). Wild-type strains, in xylose-glucose medium, utilized glucose preferentially over xylose and showed diauxic growth. With wild-type strain I-13, xylose isomerase activity was not induced until glucose was consumed from the medium. Strain X-160, however, utilized xylose concurrently with glucose and did not show diauxic growth. In this strain, xylose isomerase was induced even in the presence of glucose. Glucose transport activity in intact cells of strain X-160 was less than 10% of that assayed in strain I-13. Determinations of glycolytic enzymes did not show any difference responsible for the unique behavior of strain X-160, but the rate of glucose-6-phosphate formation with phosphoenolpyruvate (PEP) as a phosphoryl donor in permeabilized cells was less than 10% of that observed in the wild type. Starved P. halophilus I-13 cells contained the glycolytic intermediates 3-phosphoglycerate, 2-phosphoglycerate, and PEP (PEP pool). These were consumed concomitantly with glucose or 2-deoxyglucose uptake but were not consumed with xylose uptake. The glucose transport system in P. halophilus was identified as a PEP:mannose phosphotransferase system on the basis of the substrate specificity of PEP pool-starved cells. It is concluded that, in P. halophilus, this system is functional as a main glucose transport system and that defects in this system may be responsible for the depression of glucose-mediated catabolite control.     

Cytochrome P-450 and chromosome damage by cyclophosphamide in LEC strain rats predisposed to hereditary hepatitis and liver cancer

LEC strain rats predisposed to hereditary hepatitis and liver cancer were examined for hepatic drug-metabolizing ability and the inducibility of chromosome damage by cyclophosphamide (CP) in somatic cells. Whereas the hepatic cytochrome P-450 contents and the activities of cytochrome P-450-catalyzed monooxygenases were lower in females than in males of both LEC and control LEA strains, male LEC rats exhibited significantly reduced cytochrome P-450 contents and monooxygenase activities compared with male LEA rats. When exposed to CP, a promutagen/procarcinogen requiring P-450-dependent metabolic activation, the frequencies of chromosome aberrations and sister-chromatid exchanges (SCEs) in bone marrow cells tended to be lower in females than in males of each strain and lower in LEC than in LEA rats of the same sex. In particular, the CP-induced SCEs were substantially lower in LEC rats. However, no such sex and strain differences were found in the SCE frequencies in regenerating hepatocytes of partially hepatectomized rats exposed to CP.     

Effects of a New Plant Growth Regulator Prohexadione Calcium (BX-112) on Shoot Elongation Caused by Exogenously Applied Gibberellins in Rice (Oryza sativa L.) Seedlings

The effects of a novel plant growth regulator (PGR) prohexadionecalcium (BX-112; calcium 3,5-dioxo-4-propionylcyclohexanecarboxylate)on shoot elongation caused by exogenously applied GA₁, GA₃,GA₄₎ GA₁₉ and GA₂₀ were investigated in rice (Oryza sativa L.cv. Nihonbare and cv. Tan-ginbozu) seedling test. Dependingon the dose, BX-112 reduced shoot elongation in both cultivarscaused by GA₁₉ and GA₂₀, but not by GA₁. When a high dose ofBX-112 (e.g. 250 ng/plant and over) was applied with GA₁, orGA₄, shoot elongation was even promoted. This promotive effect,however, was not observed with GA₃. These results suggest thatBX-112 inhibits gibberellin (GA) biosynthesis in the rice plantat the 3ß- and 2ß-hydroxylation of GAs,namely steps of activation and inactivation, respectively. (Received September 6, 1989; Accepted November 27, 1989)     

Frequency of micronuclei in hepatocytes following X and fast-neutron irradiations--an analysis by a linear-quadratic model

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.     

Production of a triple mutant,chlorophyll-deficient,streptomycin-, and kanamycin-resistant Nicotiana tabacum,and its use in intergeneric somatic hybrid formation with Solanum melongena

Summary In order to produce a triple mutant, sexual crosses between a chlorophyll-deficient, streptomycin-resistant mutant of Nicotiana tabacum (SA) and a kanamycin-resistant transformant of N. tabacum (KR.) were carried out. From the offspring of this cross, a triple mutant (KR-SA) was selected. In N. tabacum KR-SA, chlorophyll deficiency is due to recessive mutation in the nuclear genome, streptomycin resistance is due to a dominant mutation in the chloroplast genome, and kanamycin resistance is shown to be a dominant nuclear marker. Cell suspension protoplasts of N. tabacum KRSA were fused with callus protoplasts of Solanum melongena by dextran treatment. Somatic hybrid plants were selected for streptomycin resistance and the ability to produce clorophyll in regenerated plants. By using this selection system, green plants were recovered from two colonies. When these green plants were then tested for kanamycin resistance, all analyzed plants carried this trait. In addition, the hybrid nature of these plants was confirmed by investigation of the peroxidase isozyme. The present results show that the use of N. tabacum KR-SA in studies of somatic hybridization makes it possible to select somatic hybrid plants easily and provides information of the N. tabacum genome.Chemical Regulation of Biomechanism, The Institute of Physical and Chemical Research, Wako 351-01, Japan     

PGJ2 and delta 12PGJ2 inhibit cell growth accompanied with inhibition of phosphoinositide turnover in human astrocytoma cells

PGJ2 and delta 12PGJ2 (1 microM to 30 microM) inhibited the growth of human astrocytoma cells (1321N1) in a time-dependent manner within 48 hrs, determined by [3H]thymidine incorporation into acid-insoluble fraction or amounts of protein. The EC50 values for PGJ2 and delta 12PGJ2 were approximately 8 microM and 6 microM, respectively. [3H]Thymidine incorporation to acid insoluble fraction was inhibited by these PGs within 1 hr, indicating that these PGs rapidly affect cell functions. Although it has been reported that an increase in cyclic AMP inhibits cell growth, PGJ2 and delta 12PGJ2, but not PGE1, reduced isoproterenol (10 microM)-induced accumulation of cyclic AMP, suggesting that PGJ2 and delta 12PGJ2 may disturb adenylate cyclase system, which might be independent on cell growth. On the other hand, these PGs inhibited the incorporation of [3H]inositol into phospholipid fraction within 6 hrs. Furthermore, PGJ2 and delta 12PGJ2 inhibited carbachol- and/or histamine-induced accumulation of inositol phosphates with a similar dose-dependency to their inhibitions of cell growth. In membrane preparations, however, PGJ2 and delta 12PGJ2 failed to inhibit GTP gamma S (10 microM)- nor Ca2+ (1 mM)-induced accumulation of inositol phosphates. The site of PGJ2 or delta 12PGJ2 in inhibition of inositol phosphate accumulation would not be phospholipase C nor a putative GTP binding protein involved in activation of phospholipase C. The present results indicate that PGJ2 and delta 12PGJ2 inhibit cell growth in human astrocytoma cells and the inhibition of phosphoinositide turnover by these PGs might be involved in the inhibition of cell growth.     

Organic structures of the hypercalcified peritubular matrix in horse dentine.

EDTA-insoluble organic structures of the hypercalcified peritubular matrix (PM) in horse dentine were observed by scanning electron microscopy. The PM was enveloped in double cylindrical structures composed of fibrillar sheaths in the inner and outer peripheries. Between the outer fibrillar sheath and intrinsic fibrils of the intertubular matrix, a calcified cementing membrane existed. Within the PM, warped cone-shaped structures of fibrillar sheaths, overlapping at intervals of 4-6 microns and semiconcentrically surrounding the dentinal tubule, extended from the inner fibrillar towards the outer fibrillar sheath. The cone-shaped fibrillar sheaths following the inner and outer fibrillar sheaths were identified as the incremental lines of the PM. Most of these fibrils may be collagen although it could not be confirmed, whereas non-collagenous organic materials in the lateral branches of the dentinal tubule are radially arranged in the PM. These EDTA-insoluble structures were three-dimensionally illustrated using an image-analysing system.     

Cloning and chromosomal mapping of the mouse DNA-dependent protein kinase gene

 Severe combined immune deficiency (scid) mice are assumed to have two types of abnormalities: one is high radiosensitivity and the other is abnormal recombination in immunoglobulin and T-cell receptor genes. The human chromosome 8 q1.1 region has an ability to complement the scid aberrations. Moreover, the localization of the subunit DNA-dependent protein kinase [DNA-PK_cs] participating in DNA double-strand break repair in the same locus was clarified. In scid mouse cells, the number of DNA-PK_cs products and extent of DNA-PK activity remarkably decrease. These observations gave rise to the assumption that DNA-PK_cs is the scid factor itself. In order to determine whether the DNA-PK _cs gene is the scid gene, we isolated the mouse DNA-PK _cs gene and investigated its chromosomal locus by fluorescence in situ hybridization (FISH). Consequently, it became clear that the mouse DNA-PK _cs gene existed in the centromeric region of mouse chromosome 16, determined by cross-genetic study, as a scid locus. This finding strongly suggests that mouse DNA-PK _cs is the scid gene. Received: 22 March 1996