Biochemical bases of prevention of the cytotoxic effect of xenobiotics]

Possible sources of cytotoxicity of xenobiotics and main mechanisms of realization of their damaging effect are briefly considered. Protective system of a cell is characterized with regard for the peculiarities essential for development of principles of alimentary prophylaxis of cytotoxic effects of foreign compounds. Modern approaches to alimentary modification of the processes of biotransformation of xenobiotics and promotion of protective capacities of a cell are discussed.     

Background impulse activity of neurons of the fastigial nucleus in the rat cerebellum

Background impulse activity (BIA) of neuronal elements of the fastigial nucleus (FN) of rat cerebellum were investigated for the first time with the aid of various methods of statistical analysis. A clear predominance of stationary impulse flows (IFs) was discovered, along with irregularities in such flows, variously expressed and including a significant number of realizations of a regular component of impulse activity. Nonstationary IFs constituted a special variety of BIA; they were found in 15% of the total number of neurons investigated. Serial correlation analysis of the durations of interspike intervals (ISIs), both of stationary and nonstationary IFs, allowed us to identify six main varieties of ISI dynamics in the BIA of neurons of the fastigial nucleus. The patterns of recorded IFs and variations in IFs can serve as an adequate indices of the state of cellular activity during intracellular recording from cells of the central nervous system.L. A. Orbeli Institute of Physiology, Armenian Academy of Sciences, Yerevan. Translated from Neirofiziologiya, Vol. 23, No. 4, pp. 441–450, July–August, 1991.     

Genetic analysis of Escherichia coli K-12 mutants defective for the structural and regulatory genes for second purine nucleoside phosphorylase

Two types of mutants lacking the second purine nucleoside phosphorylase (PNPase 2) activity were isolated using the Escherichia coli K-12 pndR strains with constitutive or inosine-inducible synthesis of the PNPase 2. The mutations of the first type are recessive to the pndR+ allele on the F' episome. They are closely linked to the original pndR+ mutations and therefore affect the pndR gene encoding the activator protein. The mutations of the second type affect the PNPase 2 structural gene (pndA) and are recessive to the pndA+ allele on the F' episome. The nupC-pndR-pndA-ptsH-cysA gene order was established by means of four- and five-factorial transductional crosses.     

Water-soluble glucans from the seed of Coix lacryma-jobi var. ma-yuen

The water-soluble major polysaccharides from the seed of Coix lacryma-jobi var. ma-yuen eluted as a broad peak by gel filtration on Sepharose CL-2B. The mixture (CS-Glucan) was resolved into 7 glucans by HPLC on the column of Asahi-Pak GS-510 + GS-320. Similarities were observed between M, shown in the gel filtration profile and the elution volume in HPLC. Methylation analysis indicated that the ethanol-fractionated CS-glucan contained 4-O- and 4,6-di-O-substituted glucosyl residues. ¹H and ¹³C NMR data accorded with the results of methylation analysis, and the glycosidic linkages were shown to have an α-configuration. Thus, CS-glucan contained (1 → 4) linked α-d-glucans to which are attached glucosyl side chains at O-6 of the main chain in a similar way to amylopectin. Each purified glucan was shown to have different absorption maxima ( > 550 nm or 530 nm) in the iodine reaction. The results of the methylation analysis and of the pullulanase digestion suggest that the 550 nm-glucan has a lower branching frequency and shorter side chains than the 530 nm-glucan. Although CS-glucan was found to have weak anti-complementary activity, HPLC-purified > 550 nm-glucan was found to be more potent than the 530 nm-glucan. Thus CS-glucan is highly heterogeneous, and the glucans which form a tight complex when tested with iodine, generally tend to have considerable anti-complementary activity.     

Effect of gangliosides on the cytotoxic activity of natural killers from Syrian hamsters

The ability of various gangliosides to inhibit the cytotoxic activity of natural killers (NK-cells) from Syrian hamsters towards human lymphoma MOLT-4 cells was studied. The inhibitory effect was found to depend on the structure and concentration of the gangliosides. At concentrations corresponding to those in the blood of tumour-bearing hosts, SiaLacCer and Sia2LacCer inhibited the NK-activity. A significant inhibition was also found for (NeuAc)2GgOse3Cer, whereas NeuGcGgOse3Cer and NeuAcGgOse4Cer were practically inactive. Previously it was shown that Sia2LacCer which is either absent or very low in normal blood, is produced by a number of tumours and that tumour cells "shed" considerable amounts of gangliosides. On this ground, it was proposed that elevated concentrations of SiaLacCer and Sia2LacCer in the blood of tumour-bearing animals may inhibit the NK-activity and thus contribute to the "escape" of tumour cells from host immune surveillance.     

Properties of cloned promoters

Strong early bacteriophage T7 promoters A2 and A3 and also A2 and lac UV5 promoters with altered segments downstream the initiation of RNA start point were cloned using specially constructed plasmid vectors pBRS188 and PBRS240. The relative signal strengths of these promoters in vivo and in vitro were evaluated and the kinetic parameters of their interaction with RNA polymerase were determined. It has been shown that the nucleotide sequence of the transcribed region plays a significant role in specific promoter-RNA polymerase interaction and that the rate-limiting step of RNA synthesis initiation is different for various promoters.     

Escherichia coli and Pseudomonas putida RNA polymerases display identical contacts with promoters

Summary Methylation protection experiments with four promoters (P1 and P2 of the pBR322 plasmid, lacUV5 and lambda P₀) have shown that the RNA polymerases from Escherichia coli and Pseudomonas putida, while differing in the primary structure of the subunits involved in DNA binding, display identical patterns of DNA contacts. Nor do these enzymes differ in covalent cross-linking patterns with a partially apurinized promoter. We conclude that the two RNA polymerases have very similar structures of DNA binding centers. The evolutionary conservation of this structure may account for the fact that diverse RNA polymerases often recognize and efficiently use promoters of distant bacterial species.     

Seasonal changes in ovarian state in a eusocial halictine bee,Lasioglossum duplex,based on stages of the oldest oocytes in each ovariole (Hymenoptera: Halictidae)

Summary The changes in ovarian activity in the life cycle of the eusocial halictine beeLasioglossum (Evylaeus) duplex (Dalla Torre) was studied in both queens and workers by examining the stages of the terminal follicle in each of the six ovarioles. By this method, ovarian activities of both queens and workers were more quantitatively determined than by observation of gross ovarian features as usually conducted. Queen ovaries clearly exhibited two active periods, corresponding to the spring solitary phase and the summer eusocial phase, with distinctly greater activity in the latter. In ovaries of overwintering queens oosorption of young follicle was observed. Worker ovaries were found more active in orphan than in queenright colonies. The order of ovarian activity obtained from pooled data, summer queens>spring queens>orphan workers>queenright workers, was also recognized by comparison of individual females. Bionomics of the eusocial halictine beeLasioglossum duplex IX. Contribution No. 3107 from the Inst. Low Temp. Sci.