Lipid profiles of Aspergillus niger and its unsaturated fatty acid auxotroph, UFA2

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.     

Clustering of genes for L-fucose dissimilation by Escherichia coli.

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.     

Survival and mutagenesis of bacterial plasmids with localized carcinogen adducts

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.     

Studies on heterogeneous lipopolysaccharide fractions of Vibrio cholerae 569B

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.     

Hydrogen peroxide formation and lipid peroxidation in rat uterus—effect of hormones and vitamin E

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.     

In vitro processing activity of Bacillus subtilis polynucleotide phosphorylase

A phosphate-dependent exonuclease activity was identified in purified protein fractions from Bacillus subtilis that were selected for binding to poly(I)-poly(C) agarose. Based on the characteristics of the degradation products and the absence of this activity in a pnpA strain, which contains a transposon insertion in the B. subtilis PNPase gene (Luttinger et al ., 1996 — accompanying paper), this exonuclease activity was shown to be due to polynucleotide phosphorylase (PNPase). Processive 3'-to-5' exonucleolytic degradation of an SP82 phage RNA substrate was stalled at a particular site. Structure probing of the RNA showed that the stall site was downstream of a particular stem-loop structure. A similar stall site was observed for an RNA that comprised the intergenic region between the B. subtilis rpsO and pnpA genes. The ability to initiate degradation of a substrate that had a stem structure at its 3' end differed for the B. subtilis and Escherichia coli PNPase enzymes.     

Non-equilibrium thermodynamics of Lotka-Volterra ecosystems: Stability and evolution

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.     

T cell receptor-mediated Ca2+ signaling: Release and influx are independent events linked to different Ca2+ entry pathways in the plasma membrane

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.     

Cytochromes inAzospirillum brasilense

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.