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Biomedical subjects

D Werner

Publications and source records attributed to D Werner.

At least 145 records · Page 8Linked to original sources
PubMed1982

Enhancement of specific nitrogenase activity in Azospirillum brasilense and Klebsiella pneumoniae, inhibition in Rhizobium japonicum under air by phenol.

Specific nitrogenase activity in Azospirillum brasilense ATCC 29145 in surface cultures under air is enhanced from about 50 nmol C2H4 X mg protein -1 X h-1 to 400 nmol C2H4 by the addition of 1 mM phenol. 0.5 and 2 mM phenol added increase the rate 5-fold and 4-fold. This enhancement effect is observed only between 2 and 3 days after inoculation, with only a small reduction of the growth of the cells by the phenol added. In surface cultures under 1% O2, nitrogenase activity is slightly reduced by the addition of 1-0.01 mM phenol. Utilization of succinate is enhanced during the period of maximum enhancement of nitrogenase activity by 60% by addition of 1 mM phenol. The cells did not produce 14CO2 from [U-14C] phenol, neither in surface cultures nor in liquid cultures and less than 0.1% of the phenol was incorporated into the cells. A smaller but significant enhancement of nitrogenase activity by about 100% in surface cultures under air was found with Klebsiella pneumoniae K 11 after addition of 1 mM phenol. However, in Rhizobium japonicum 61-A-101 all phenol concentrations above 0.01 mM reduced nitrogenase activity. With 1 mM phenol added activity was reduced to less than 10% with no effect on the growth in the same cultivation system. With this Rhizobium japonicum strain significant quantities of phenol (25 mumol in 24 h by 2 X 10(12) cells) were metabolized to 14CO2, with phenol as sole carbon source. With Azospirillum brasilense in liquid culture under 1% and 2% O2 in the gas phase, no enhancement of nitrogenase activity by phenol was noticed.

Bacteria↗
PubMed1981

Root exudates in relation to growth and nitrogenase activity of Rhizobium japonicum.

Root exudates of cowpea and soybean were collected in aerated water cultures. The ability of these exudates to support nitrogenase activity of R. japonicum was studied on defined media. When a complete nitrogenase-inducing medium was supplemented with concentrated root exudate, there was an increased nitrogenase activity. When the cowpea root exudate was substituted for glutamine or sodium succinate in the medium, nitrogenase activity was not detected. Growth was good when the root exudate was substituted for sodium succinate but was poor when the exudate replaced glutamine. There was nitrogenase activity in R. japonicum when the cowpea root exudate was substituted for arabinose in the 20E medium. Gas chromatographic analyses of cowpea root exudates revealed that ribose, arabinose, glucose, and sucrose were the main constituents. The significance of this finding in the asymbiotic nitrogen fixation by Rhizobium spp. is discussed.

Arabinose↗
PubMed1981

Non-random distribution of N-methyl-N-nitrosourea sensitive sites in a eukaryotic genome.

DNA released from Ehrlich ascites cells by lysis in the presence of 50 microgram X ml-1 of proteinase K contains long alkali-stable strands in the order of 50-100 X 10(6) daltons. In contrast, DNA released in the presence of 6 mg X ml-1 of autodigested pronase is significantly nicked. According to sedimentation rates the number of internal ends liberated during this procedure is 24/200 X 10(6) daltons. The number of alkali-labile sites introduced into DNA by incubation of Ehrlich ascites cells with 1 nM of N-methyl-N-nitrosourea (MNU) followed by cell lysis in the presence of 50 microgram X ml-1 of proteinase K and alkali-denaturation is 16.6/200 X 10(6) daltons. From this one should expect that denatured DNA released from cells pretreated with 1 mM of MNU which are subsequently lysed with 6 mg X ml-1 of pronase would have about 40 single-strand breaks/200 X 10(6) daltons. However, denatured DNA strands released by 6 mg X ml-1 of pronase either from MNU-treated or untreated cells cannot be separated by centrifugation through alkaline sucrose gradients. This phenomenon could be explained by a non-random distribution of MNU-inducible alkali-labile sites of DNA in vivo.

Animals↗
PubMed1981

Cell density dependent DNA replication in Ehrlich ascites tumour cells.

DNA replication of Ehrlich ascites tumour cells was investigated in suspensions with different cell densities by incorporation in vitro of tritiated thymidine and alkaline sucrose gradient analysis of the newly formed DNA. It is demonstrated that the incorporation of [3H]thymidine and chain growth of newly made DNA decreases with increasing cell density. The inhibition of DNA synthesis observed at high cell densities can be prevented if diffusible substances are removed by incubating the cells in dialysis tubes. This indicates that the changes in DNA synthesis are caused by diffusible inhibitors released from the tumour cells.

Animals↗
PubMed1981

Size of native and denatured DNA of Ehrlich ascites tumour cells isolated in the presence of different protease concentrations.

Native DNA molecules isolated either in the presence of 50 micrograms x ml(-1) of proteinase K (PK-DNA) or in the presence of 6 mg x ml(-1) autodigested pronase (PRO-DNA) are about equal in size. Since shear forces were avoided as far as possible during the isolation procedure, the largest molecules found were longer than 100 microns. The average length of the traced molecules was 34.2 microns for PK-DNA and 29.7 microns for PRO-DNA. In contrast to PK-DNA the length of PRO-DNA molecules undergoes a dramatic change during denaturation. The average contour length of a denatured PRO-DNA molecules is only 6.9 microns. This reduction in length cannot be explained by shrinkage due to changes in ionic strength, pH and the effect of denaturing agents. Moreover, PK-DNA identically denatured was not dramatically changed in size. From this it must be concluded that PRO-DNA contains more internal ends than PK-DNA. This conclusion is supported by the results indicating that PRO-DNA is much more sensitive to nuclease S1 than PK-DNA. The results are consistent with previously published biochemical data suggesting that chromosomal DNA is 'nicked' or 'gapped' in a protease-catalyzed reaction at distinct protease-sensitive sites.

Animals↗
PubMed1980

Internucleotide protein linkers in Ehrlich ascites cell DNA.

DNA from Ehrlich ascites tumor cells is nicked or gapped by a reaction which is induced by proteases such as autodigested pronase, proteinase K, trypsin, chymotrypsin and subtilisin. The cleavage of the protease-sensitive sites is inhibited by protease inhibitors. The nicks or gaps induced by proteases can be demonstrated by nuclease S1 sensitivity of native DNA and by a change of the sedimentation rate of alkali-denatured DNA. The limit size of denatured DNA released after optimal protease treatment is 8.5 x 10(6) daltons (27 kilo bases). The molecular weight of the native DNA pieces released after nuclease S1 degradation of DNA containing the protease-induced nicks or gaps is in the same order indicating that the protease-sensitive sites are alternatively arranged on the opposite DNA strands at an average distance of 13.5 kilo base pairs. Since the protease-induced nicks or gaps in phosphatase-treated DNA are not attacked by Escherichia coli polymerase I, one or both ends liberated by the protease treatment must be blocked by a material other than phosphate groups. The results are most compatible with peptide/protein linkers joining adjacent single-strand DNA subunits. Alternative explanations such as alkali-stable RNA linkers, protein-protected RNA linkers, site-specific nuclease contaminations in the protease preparations or cellular nucleases activated by the protease treatment are eliminated by the results presented in this paper.

Animals↗
PubMed1979

Analysis of the most tightly bound proteins in eukaryotic DNA.

DNA isolated by procedures generally considered to be most efficient for purifying DNA still contains detectable peptide components. The characteristics of this material and the stability of its linkage to DNA were investigated: DNA released from [35S]methionine-labelled cells by SDS in the presence of proteases contains a significant amount of 35S label which is not removed by additional treatment with proteases and phenol and which cosediments and cobands together with DNA on alkaline gradients. Furthermore, some peptide material which is copurified with native DNA and which remains complexed with DNA after alkali treatment can be labelled with 125I and analyzed on SDS-polyacrylamide-gels. The amino acid analysis of hydrolysates of purified DNA gives a rough estimate of the amount of the peptide material which is copurified with DNA. The results indicate that distinct proteins between 54 000 and 68 000 daltons in size are not removed from DNA by phenol, proteases, alkali or by any combination of these treatments. They can only be isolated by degradation of DNA. This extreme stability of the DNA-protein linkage indicates that these proteins are not merely contaminants which are difficult to eliminate but are rather covalently or otherwise bound (alkali-stable) to DNA. The size of these proteins and the stability of their linkage to DNA suggests that they are related to the class of non-histone proteins which are thought to be involved in chromatin structure e.g. by keeping DNA in a supercoiled state. Other possible functions are discussed.

Amino Acids↗
PubMed1979

A simple method for the separation of tissue-cultured plant cells from unbound bacteria: a demonstration of acquired affinity for bacteria by cells of soy bean.

Tissue-cultured cells of soy bean, grown in liquid medium and then transferred to an agar substratum in so-called tissue chambers, showed an affinity for the binding of applied bacteria (Klebsiella pneumoniae). This binding, which became greater as the plant cells remained on the agar for up to 10 days, was manifested as an increasing resistance of the bacteria to be washed from the plant cells in a standard, gentle and reproducible procedure devised for this purpose. The number of bacteria firmly bound to the cells was determined by the use of 32P-labelled bacteria and was largely independent of the concentration of bacteria in the suspension applied to the tissue-cultured cells.

Adsorption↗
PubMed1979

A cross-cultural perspective on theory and research on male homosexuality.

In an effort to uncover useful directions for future research, this paper examines the cross-cultural data on male homosexuality in light of various theories that might account for its variation. Looking first at different psychological explanations, the study suggests that the sex of one's childhood companions may be an important factor in the origin of homosexuality. Two possible explanations for an association between male homosexuality and mixed-sex playgroups are offered: In one, gender identity serves as an intervening variable; in the other, the notion that "familiarity breeds contempt" is studied. A cultural materialist theory, which views homosexuality as adaptive under conditions of population pressure, is shown to be supported by the correlation between a society's natalist policy and its attitudes toward homosexuality.

Attitude↗