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11.
P Chattopadhyay S K Banerjee K Sen P Chakrabarti 《Canadian journal of microbiology》1985,31(4):352-355
A comparative study of the mycelial lipid composition of a wild strain (V35) and one unsaturated fatty acid auxotroph (UFA2) of Aspergillus niger has been performed. The lipid composition of both strains are qualitatively the same but quantitatively different. All the strains contain the following phospholipids: cardiolipin, phosphatidylethanolamine, phosphatidylcholine, lysophosphatidylethanolamine, lysophosphatidylcholine, and phosphatidylserine; and triglycerides, diglycerides, monoglycerides, ergosterol, and sterol esters as the neutral lipids; mono- and di-galactosyl diglyceride as the major glycolipids along with small amounts of the corresponding mannose analogs. Phosphatidylethanolamine and phosphatidylcholine constitute the bulk of the phospholipids. The mutant (UFA2) contains a higher level of glycerides and lower levels of sterol (both free and esterified form), phospholipids, and glycolipids than the wild type. Aspergillus niger contains C16 to C18 saturated and unsaturated fatty acids. Small amounts of long-chain (C20 to C24) and short-chain (C10 to C14) saturated and unsaturated acids are also present. Linoleic, oleic, and palmitic are the major acids, stearic and linolenic acids being minor ones. UFA2 grows only in the presence of unsaturated fatty acid (C16 or C18) and accumulates a higher concentration of supplemented acid which influences its fatty acid profile. 相似文献
12.
Aerobic and anaerobic L-fucose utilization by Escherichia coli involves an inducible trunk pathway mediated by a permease, an isomerase, a kinase, and an aldolase. Tn5 insertion mutants of a parental strain expressing this pathway constitutively were used to map the positions of the structural genes by transduction. Results from this and previous studies show that all of the structural genes of the L-fucose trunk pathway map between eno and argA at minute 60.2 of the chromosome. 相似文献
13.
Induction of 6-thioguanine (TG) resistance by chemical mutagens was examined in a line of cells derived from a human epithelial teratocarcinoma cell clone. The cells, designated as P3 cells, have a stable diploid karyotype with 46(XX) chromosomes, including a translocation between chromosomes 15 and 20. Efficient recovery of TG-resistant mutants induced by the direct-acting mutagens: N-methyl-N'-nitro-N-nitrosoguanidine (MNNG); 7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-epoxy-7,8,9,10 -tetrahydrobenzo[a]pyrene (BPDE); and benzo[a]pyrene (B[a]P); activated in a cell-mediated assay, required an expression time of 7 days and a saturation density of 2 X 10(4) cells/60-mm petri dish. The TG-resistant mutant cells induced by MNNG and BPDE maintained their resistant phenotype 4-6 weeks after isolation. This mutant phenotype was associated with a more than 10-fold reduction in hypoxanthine-guanine phosphoribosyl transferase (HGPRT) activity relative to that of the parental P3 cell line, which was shown to catalyze the formation of 4.6 pmoles inosine-5'-monophosphate (IMP)/min/microgram protein. Induction of TG resistance was also observed in P3 cells cocultivated in a cell-mediated assay with human breast carcinoma cells, which are capable of polycyclic aromatic hydrocarbon (PAH) metabolism, after treatment with the carcinogenic PAHs: B[a]P, chrysene, 7,12-dimethylbenz[a]anthracene (DMBA), and 3-methylcholanthrene (MCA). The degree of mutant induction in this assay was related to the carcinogenic potency of these PAHs in experimental animals. The most potent mutagen was DMBA, followed in decreasing order by MCA, B[a]P, and chrysene. DMBA, at 0.4 microM, increased the frequency of mutants for TG resistance from 2 for the control to about 200 TG-resistant mutants/10(6) colony-forming cells (CFC). Benzo[e]pyrene (B[e]P) and pyrene, which are not carcinogenic, were not effective in the assay. None of the PAHs was mutagenic in the P3 cells cultivated in the absence of the PAH-metabolizing cells. These results indicate that the P3 cells can be useful for the study of mutagenesis at the HGPRT locus by direct-acting chemical mutagens, as well as by chemicals activated in a cell-mediated assay. 相似文献
14.
By SDS-PAGE or gel filtration on Sephadex G-25, lipopolysaccharide (LPS) isolated from Vibrio cholerae 569B (Inaba) can be separated into two distinct fractions, one corresponding to smooth LPS and the other to rough LPS. Pulse-labelling of LPS with [14C]glucose showed that the rough form is synthesized first followed by the biosynthesis of the smooth form. A preferential release of the smooth LPS of V. cholerae 569B was also detected during normal growth of cells. 相似文献
15.
Shyamali Mukherjee Mihir Nag Tultul Nayyar Indrani Maitra Parul Chakrabarti Pramod R. Dasgupta 《Journal of biosciences》1986,10(3):311-317
The effect of estradiol-17β and progesterone given separately as well as in combination on the rate of hydrogen peroxide formation
and lipid peroxidation in the uteri of ovariectomized rats was studied. Estradiol in 3μg dose per day per animal elicited maximum stimulatory response and progesterone (100μg), on the other hand, was without any such effect. However, progesterone given along with estradiol completely prevented the
effect due to the latter. In the same way, vitamin E, a well known antioxidant was found to be extremelv effective in protecting
the uterus from the highly peroxidative action of estradiol-17β. 相似文献
16.
17.
A non-equilibrium thermodynamic theory of generalized Lotka-Volterra ecosystem has been presented. The main results consist of the derivation of a generalized expression of entropy-production for the evolutionary ecosystem and the study of its role in the analysis of ecological stability, succession and also in the formulation of some extremum principles characterising the evolution of the ecosystem. 相似文献
18.
Rabindranath Chakrabarti Joseph Y. Chang Kent L. Erickson 《Journal of cellular biochemistry》1995,58(3):344-359
In this study, we showed that cross-linking CD3 molecules on the T cell surface resulted in Ca2+ release from the intracellular stores followed by a sustained Ca2+ influx. Inhibition of release with TMB-8 did not block the influx. However, inhibition of phospholipase C activity suppressed both Ca2+ release and influx. Once activated, the influx pathway remained open in the absence of further hydrolysis of PIP2. Thapsigargin, a microsomal Ca2+ -ATPase inhibitor, stimulated Ca2+ entry into the cells by a mechanism other than emptying Ca2+ stores. In addition, Ca2+ entry into the Ca2+ -depleted cells was stimulated by low basal level of cytosolic Ca2+, not by the emptying of intracellular Ca2+ stores. Both the Ca2+ release and influx were dependent on high and low concentrations of extracellular Ca2+. At low concentrations, Mn2+ entered the cell through the Ca2+ influx pathway and quenched the sustained phase of fluorescence; whereas, at higher Mn2+ concentration both the transient and the sustained phases of fluorescence were quenched. Moreover, Ca2+ release was inhibited by low concentrations of Ni2+, La3+, and EGTA, while Ca2+ influx was inhibited by high concentrations. Thus, in T cells Ca2+ influx occurs independently of IP3-dependent Ca2+ release. However, some other PIP2 hydrolysis-dependent event was involved in prolonged activation of Ca2+ influx. Extracellular Ca2+ influenced Ca2+ release and influx through the action of two plasma membrane Ca2+ entry pathways with different pharmacological and biochemical properties. 相似文献
19.
Syamal K. Chakrabarti Ajit K. Mishra Dr. Pran K. Chakrabartty 《Current microbiology》1984,11(6):343-347
Difference spectra of the crude cell-free extract ofAzospirillum brasilense sp. 7 indicate the presence of cytochrome b, cytochrome c, and one CO-binding pigment that exhibits the spectral characteristics of cytochrome o. All the pigments are present in varying concentrations at all stages of growth. With progress of the bacterial growth, there is a linear increase in the level of cytochrome b with a disproportionate increase in the level of cytochrome c. At the stationary phase, the amount of cytochrome b and c is increased by about sevenfold compared with that in the early log phase. The increase in the concentration of total cytochrome is not accompanied by an increase in the respiration rate of the cells. Both cytochrome b and cytochrome c are located in the particulate fraction of the cells and are not fully reducible by succinate alone. 相似文献
20.
Circular dichroism studies of glycosaminoglycan including chemically transformed heparins at various pH values reveal that carboxyl chromophore plays an important role in the dichroic behavior of the polymers. With decreasing pH, iduronic acid-containing glycosaminoglycans show increased negative ellipticity near 220 nm whereas the polymers containing glucuronic acid display enhanced negative dichroism near 230 nm and decreased negative dichroism around 210 nm. The pH-dependent optical properties have been utilized to determine the pKa values of uronic acid moieties. The acid strengths of the iduronic acid-containing glycosaminoglycans are inherently smaller than those of corresponding glucuronic acid-containing polymers. Glycosaminoglycans in which the amino sugars are linked with iduronic acid display a very weak n → π* amide transition, or none. The rotational strength at 210 nm of these polymers is largely due to iduronic acid moieties. The CD variations above 200 nm with change in pH do not indicate any major conformational transition of the molecules but the difference between dermatan sulfate and heparin can be attributed to difference either in iduronic acid conformation or in intersaccharide linkages. 相似文献