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Maris G. N. Hartmanis Henrik Åhlman Sten Gatenbeck 《Applied microbiology and biotechnology》1986,23(5):369-371
Summary
Clostridium acetobutylicum ATCC 824 was submitted to repeated subculturing at 24-hour intervals for 218 days. The organism retained its ability to form solvents, although the fermentation slowly became increasingly acidogenic during the first 200 days. Except for the initial spore inoculum, the cultures were not subjected to heat shocking between the serial transfers. When the inoculum volume was doubled from 3.3% to 6.7% after 200 days of subculturing, the product formation pattern quickly shifted back from acids to primarily butanol. Acetone production also resumed after being undetectable for more than 50 days. The relative formation of acetate and ethanol remained nearly constant throughout the experiments, while the formation of butyrate mirrored that of butanol. 相似文献
54.
Growth factors induce early pre-replicative changes in senescent human fibroblasts. 总被引:5,自引:0,他引:5 下载免费PDF全文
Y Paulsson M Bywater S Pfeifer-Ohlsson R Ohlsson S Nilsson C H Heldin B Westermark C Betsholtz 《The EMBO journal》1986,5(9):2157-2162
As human fibroblasts in culture senesce their response to platelet-derived growth factor (PDGF) becomes attenuated. To clarify at which level such cells are blocked in the pre-replicative part of the cell cycle, we have analysed PDGF-induced pre-replicative events in senescent (phase III) cultures. We found that phase III cells retain a normal number of PDGF receptors and that these are functional with regard to PDGF-induced receptor autophosphorylation. Phase III cells also respond to PDGF by rapid actin reorganization and increased levels of c-fos and c-myc mRNA, similar to growth-arrested phase II fibroblasts. However, the expression of the nuclear antigen K-67, which in phase II cell is induced in S-phase and continues to be expressed throughout the cell cycle, is not induced in phase III cells in response to PDGF. We conclude that phase III human fibroblasts, although blocked with regard to proliferation, still retain a functional growth factor receptor system, and display early responses when exposed to growth factors, such as changes in the cytoskeleton and the expression of proto-oncogenes. 相似文献
55.
Brain capillaries (microvessels) were isolated from the rabbit and bovine brain. Extensive morphological examinations were performed at the light and electron microscopical levels. The relative contribution of endothelium (52%), basal membrane (32%) and pericytes (16%) to the composition of the microvessel was assessed. The ability of the endothelium from bovine brains to maintain a membrane potential, i.e. to accumulate the lipophilic cation [3H]TPMP, was shown. The transmitter catabolizing enzymes MAO and AchE were shown to be, and COMT and GABA-T not to be associated with the microvessel fraction isolated from rabbits. 相似文献
56.
Curt Nilsson 《Hydrobiologia》1983,98(3):267-269
Two experimental groups of Culiseta bergrothi Edw. larvae were kept under laboratory conditions, but in water from the breeding locality. The ‘donors’ were fed on a suspension of charcoal powder and baker's yeast; the ‘receivers’ had access to the faecal pellets of the donors. After 1.5 hours the gut of almost all receivers was more or less filled with charcoal particles. The possible consequences of the added yeast suspension to food choice and feeding behaviour are discussed. 相似文献
57.
A tRNAPhe derivative carrying ethidium at position 37 in the anticodon loop has been used to study the effect of spermine on conformational transitions of the tRNA. As previously reported (Ehrenberg, M., Rigler, R. and Wintermeyer, W. (1979) Biochemistry 18, 4588-4599) in the tRNA derivative the ethidium is present in three states (T1-T3) characterized by different fluorescence decay rates. T-jump experiments show two transitions between the states, a fast one (relaxation time 10-100 ms) between T1 and T2, and a slow one (100-1000 ms) between T2 and T3. In the presence of spermine the fast transition shows a negative temperature coefficient indicating the existence of a preequilibrium with a negative reaction enthalpy. Spermine shifts the distribution of states towards T3, as does Mg2+, but the final ratio [T2]/[T1] obtained with spermine is higher than with Mg2+, which we tentatively interpret to mean that spermine stabilizes one particular conformation of the anticodon loop. 相似文献
58.
Horse liver alcohol dehydrogenase was immobilized on glycerylpropyl-silica (10 micron, 1000-A pores) activated with 2,2,2-trifluoroethanesulfonyl chloride (tresyl chloride). The coupling and activity yield was almost 100%. The coenzyme-binding sites were equivalent and virtually unaffected by the immobilization process, as judged from Scatchard plots and active-site titrations. The silica-bound enzyme, packed in steel columns, was integrated with HPLC equipment and then successfully used for chromatography of adenine nucleosides, adenine nucleotides, and triazine dyes. Dissociation constants were calculated from chromatographic data and found to correspond well with literature values. The dissociation constants for a number of nucleotide derivatives with potential application in affinity chromatography were also determined. The spaces were found to affect the binding strength of the nucleotides in a qualitatively predictable way. Theoretical plate heights were calculated and found to be in the range 0.01 to 0.1 cm. Attempts to correlate peak widths with the rate constants for the binary complexes involved were only partially successful. 相似文献
59.
A 23 kDa protein has recently been demonstrated to participate in photosynthetic oxygen evolution by reconstitution experiments on inside-out thylakoid vesicles (Åkerlund H-E, Jansson C and Andersson B (1982) Biochim Biophys Acta 681:1–10). Here we describe the isolation of the 23 kDa protein from a spinach chloroplast extract using ion-exchange chromatography. The protein was obtained in a yield of 25% and with less than 1% of contaminating proteins. The ability of the protein to stimulate oxygen evolution in inside-out thylakoids was preserved throughout the various fractionation steps. The isolated protein was highly water soluble and appeared as a monomer. Its isoelectric point was at pH=7.3. The amino acid composition showed a high content of polar amino acids, resulting in a polarity index of 49%. The isolated protein lacked metals and other prosthetic groups. Its function as a catalytic or regulating subunit in the oxygen evolving complex is discussed. 相似文献
60.
Polyoma virus mutants were constructed that could not express all the three T-antigens. The mutagenesis was directed to the two 5' splice sites utilized in the maturation of early RNA. The mutant bc1051 had a base change at the splice site of large T-antigen mRNA, and the mutants dl1061 and dl1062 had deletions at the corresponding splice point of small and middle T-antigen mRNA. The site was removed in mutant dl1061 and altered by fusion to upstream sequences in mutant dl1062. Analysis of viral RNA showed that dl1061 and dl1062 formed only large T-antigen mRNA, whereas bc1051 did not produce this RNA-species. However, the biological properties of dl1062 suggested that it also produced mRNA directing the synthesis of a small T-antigen-related polypeptide, at least in low amounts. Only mutant bc1051 could induce transformation of rat cells. In mouse 3T3 cells dl1062 multiplied to a limited extent, while bc1051 and dl1061 failed to produce virus. However, dl1061 DNA was synthesized at a low rate which could be increased to normal levels by co-transfection with mutant bc1051. This result suggests that polyoma small and middle T-antigen have a previously unrecognized function in the early phase of the infection process, or in viral DNA-synthesis. 相似文献