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91.
92.
The growth interactions amongst the blue-green algal species Anabaena oscillarioides, Microcystis aeruginosa and the green alga, Chlorella sp. were studied both in mixed cultures and in filter cultures separated by a membrane filter in the two arms of an interaction U-tube. The role of nutrients especially phosphate upon the interaction has also been studied.
Anabaena and Microcystis both inhibited the growth of Chlorella while Microcystis also inhibited the growth of Anabaena. The inhibitory effect of Microcystis was found to be dependent on high concentrations of the initial algal inocula and independent of the initial concentration of nutrients such as inorganic phosphate, indicating that the nature of the inhibition is probably due to the production of inhibitory extracellular products by Microcystis. On the other hand, the inhibitory effect of Anabaena on Chlorella is the consequence of nutrient competition with Anabaena competing more effectively for the available phosphate. 相似文献
93.
Vijay K. Mahajan Dominic M. Desiderio 《Biochemical and biophysical research communications》1978,82(4):1104-1110
The amino acid sequence of oligopeptides can be determined from the mass spectra of their volatile derivatives. New peptide derivatives are described which are prepared from permethylated peptides by reduction with borane-tetrahydrofuran. These derivatives have been found to be more volatile than the corresponding permethylated ones. The procedure is illustrated by application of this technique to representative oligopeptides. As little as 10–100 nmol of these peptides have been sequenced using this technique. 相似文献
94.
The importance of the lysophosphatidylcholine and choline moiety of bile phosphatidylcholine in lymphatic transport of fat 总被引:3,自引:0,他引:3
A luminal supply of biliary phosphatidylcholine is important in the translocation of absorbed fat into lymph and in the amount and composition of phosphatidylcholine concurrently synthesized. This study was undertaken to determine whether the effect was due to absorbed lysophosphatidylcholine, to a specific (1-palmitoyl) biliary lysophosphatidylcholine or to extra choline supplied by lysophosphatidylcholine. Rats with bile fistulae and thoracic duct lymph fistulae were given test meals of oleic acid and monoolein (molar ratio 2 : 1) infused duodenally for 8 h. Addition of choline chloride to the test meal increased lymphatic output of triglyceride and phospholipid but not to values found previously in rats with supplements of bile phosphatidylcholine or with bile ducts intact. Addition of dioleoyl phosphatidylcholine increased triglyceride and phospholipid output to values found in rats with intact bile ducts. Since dioleoyl phosphatidylcholine was as efficient as biliary phosphatidylcholine it was concluded that a luminal supply of 1-palmitoyl lysophosphatidylcholine was not essential. It seemed likely from the smaller effect of supplemented choline and from the fatty acid composition of lymph phosphatidylcholine that the essential requirement was a supply of absorbed lysophosphatidylcholine for rapid reacylation to phosphatidylcholine. 相似文献
95.
The separation of active and inactive forms of heparin. 总被引:38,自引:0,他引:38
L H Lam J E Silbert R D Rosenberg 《Biochemical and biophysical research communications》1976,69(2):570-577
Heparin has been fractionated into two distinct forms. The isolation of these species was accomplished by sucrose density gradient centrifugation of heparin mixed with antithrombin-heparin cofactor. Approximately of this mucopolysaccharide was bound to antithrombin-heparin cofactor and had potent anticoagulant activity. This component was clearly separated from the remaining of the heparin which could not form a stable complex with antithrombin-heparin cofactor and had minimal anticoagulant activity. 相似文献
96.
A key attribute of the stringent response of bacteria is the rapid inhibition of ribosomal RNA synthesis mediated by unusual nucleotides in response to uncharged tRNA. The question as to whether mammalian cells show a stringent response analogous to that of bacteria was critically tested by the effective rapid amino acid starvation of both normal and transformed cells. Rapid starvation giving a high proportion of uncharged tRNA for leucine was produced within 7 minutes of expression of a nonleaky ts leucyl tRNA synthetase mutation in transformed CHO cells (tsH1) and in its normal growth control revertant (L-73). To control for the effect of temperature alone, tsrevertants of tsH1 and L-73 were included in the study, and to control for effects due simply to the inhibition of protein synthesis, the translational elongation inhibitor cycloheximide was used. In addition, rapid starvation for histidine was effected by incubation of both the CHO cell lines and of freshly explanted normal Chinese hamster embryo fibroblasts in histidine-free medium containing high concentrations of histidinol. The rate of preribosomal RNA synthesis and the extent of its maturation to mature rRNA was measured using (3H-methyl) methionine as a donor of methyl groups during synthesis and methylation of pre-rRNA. There was no effect on pre-rRNA synthesis of the rapid generation of uncharged tRNA for 45 minutes for any of the cell types tested. A nonspecific inhibition of maturation of 18S rRNA and late (3 hour) inhibition of pre-rRNA synthesis was observed, but could be mimicked by the inhibition of protein synthesis to comparable levels with cycloheximide. Less severe amino acid starvation resulting in a more physiological inhibition of protein synthesis to 30% also had no specific effect on pre-rRNA synthesis and maturation. Intracellular nucleotide pools were also examined for the appearance of unusual nucleotides such as guanosine tetraphosphate or pentaphosphate and for changes in the levels of normal nucleotides after severe amino acid starvation. No such changes could be detected. We conclude that although mammalian cells may have some biochemical reactions which respond to uncharged tRNA, they do not possess a macromolecular control system analogous to the stringent response of bacteria. 相似文献
97.
98.
Meagan E. Valentine Brandon D. Kirby Thomas R. Withers Shannon L. Johnson Timothy E. Long Youai Hao Joseph S. Lam Richard M. Niles Hongwei D. Yu 《Microbial biotechnology》2020,13(1):162-175
Alginate is an important polysaccharide that is commonly used as a gelling agent in foods, cosmetics and healthcare products. Currently, all alginate used commercially is extracted from brown seaweed. However, with environmental changes such as increasing ocean temperature and the increasing number of biotechnological uses of alginates with specific properties, there is an emerging need for more reliable and customizable sources of alginate. An alternative to seaweed for alginate production is Pseudomonas aeruginosa, a common Gram-negative bacterium that can form alginate-containing biofilms. However, P. aeruginosa is an opportunistic pathogen that can cause life-threatening infections in immunocompromised patients. Therefore, we sought to engineer a non-pathogenic P. aeruginosa strain that is safe for commercial production of alginate. Using a homologous recombination strategy, we sequentially deleted five key pathogenicity genes from the P. aeruginosa chromosome, resulting in the marker-free strain PGN5. Intraperitoneal injection of mice with PGN5 resulted in 0% mortality, while injection with wild-type P. aeruginosa resulted in 95% mortality, providing evidence that the systemic virulence of PGN5 is highly attenuated. Importantly, PGN5 produces large amounts of alginate in response to overexpression of MucE, an activator of alginate biosynthesis. The alginate produced by PGN5 is structurally identical to alginate produced by wild-type P. aeruginosa, indicating that the alginate biosynthetic pathway remains functional in this modified strain. The genetic versatility of P. aeruginosa will allow us to further engineer PGN5 to produce alginates with specific chemical compositions and physical properties to meet different industrial and biomedical needs. 相似文献
99.
100.