The glycoprotein 71 of ecotropic Friend murine leukemia virus. Structure of the oligosaccharides linked to asparagine-12

The glycoprotein from Friend murine leukemia virus was digested with protease from Staphylococcus aureus V8. A glycopeptide comprising the N-terminal glycosylation site (Asn-12) was isolated from the mixture of fragments and analyzed by amino acid sequencing and methylation-capillary gas chromatography-mass spectrometry before and after treatment with sialidase from Vibrio cholerae. Asn-12 was thus found to be substituted by a family of partially sialylated, fucosylated, and intersected glycoprotein N-glycans of the hybrid type.     

Reduction kinetics of the photo-oxidized chlorophyll a+II in the nanosecond range: Measurements of the absorption changes at 688 nm under repetitive flash excitation

The 688 nm absorption changes (ΔA₆₈₈), indicating the photochemical turnover of chlorophyll a_II (Chl a_II) have been investigated under repetitive laser flash excitation conditions in spinach chlorplasts. It was found that under steady state conditions about 50–60% of the photo-oxidized primary donor of Photosystem II (PS II), Chl a⁺_II, becomes re-reduced with a biphasic kinetics in the nanosecond time scale with half-life times of about 50 ns and 400 ns. The remaining Chl a⁺_II becomes re-reduced in the microsecond range.     

Protein-free models for the proton-coupled reduction of haemoproteins

Reduction of the bis-pilocarpate-haemin complex at pH greater than or equal to 10 involves the simultaneous uptake of an electron by the Fe(III) ion and a proton by the pendant alkoxide group of an axial ligand. This provides a protein-free model for reactions such as the proton-coupled reduction of cytochromes which involve cooperative Coulombic interaction between two non-bonded sites.     

Pollen irradiation and the transfer of maternal genes in Pisum sativum

Summary Pollen of Pisum sativum was exposed to doses of 900 to 6,000 r of X-rays prior to pollinating a multiply marked genotype. The first generation progeny closely resembled that produced with unirradiated pollen. In the second generation, five loci were monitored, and the results showed that irradiation enhanced the proportion of maternal information transmitted to the progeny; the practical implications of the data, as well as the mechanism underlying the effect are discussed.     

Vascular morphology of the bovine spermatic cord and testis

Summary The highly coiled testicular artery within the bovine spermatic cord has a constant luminal diameter but a continuously decreasing mural thickness. The pampini form plexus is composed of three interconnected venous networks differing in mesh sizes and calibres. The large veins of the first network display pouches and permanent constrictions, which may serve as throttle devices. The constitutents of the third network are venules or venous capillaries with diameters between 10 and 20 m; they favor a periarterial position or even occupy the media-adventitia border of the testicular artery. All plexus veins are devoid of valves. The existence of true arteriovenous anastomoses between smaller branches of the testicular artery and plexus veins was established by serial sections. The vascular morphology of the spermatic cord is discussed with special attention to a postulated venous-arterial steroid transfer in this region.Supported by the Deutsche Forschungsgemeinschaft and the Stiftung zur Förderung der wissenschaftlichen Forschung an der Universität Bern     

Non-aceticlastic methanogenesis from acetate: acetate oxidation by a thermophilic syntrophic coculture

Methanogenesis from acetate by a rod-shaped enrichment culture grown at 60° C was found to require the presence of two organisms rather than a single aceticlastic methanogen. A thermophilic Methanobacterium which grew on H₂/CO₂ or formate was isolated from the enrichment. Lawns of this methanogen were used to co-isolate an acetate oxidizer in roll tubes containing acetate agar. The rod-shaped acetate oxidizer was morphologically distinct from the methanogen and did not show F₄₂₀ autofluorescence. The coculture completely degraded 40 mol/ml acetate, and produced nearly equal quantities of methane, and methanogenesis was coupled with growth. The doubling time for the coculture at 60°C was 30–40 h and the yield was 2.7±0.3 g dry wt/mol CH₄. Studies with ¹⁴C-labelled substrates showed that the methyl group and the carboxyl group of acetate were both converted primarily to CO₂ by the coculture and that CO₂ was concurrently reduced to CH₄. During growth, there was significant isotopic exchange between CO₂ and acetate, especially with thecarboxyl position of acetate. These results support a mechanism for methanogenesis from acetate by the coculture in which acetate was oxidized to CO₂ and H₂ by one organism, while H₂ was subsequently used by a second organism to reduce CO₂ to CH₄. Since the H₂ partial pressure must be maintained below 10^-4 atm by the methanogen for acetate oxidation to be thermodynamically feasible, this is an example of obligate interspecies hydrogen transfer. This mechanism was originally proposed for a single organism by Barker in 1936.     

Basic steroid saponins from aerial parts of Fritillaria Thunbergii

From the aerial parts of Fritillaria thunbergii, three glycosidal Solanum alkaloids (basic steroid saponins) were isolated together with minor     

Regulation of the cytosolic adenylate ratio as determined by rapid fractionation of mesophyll protoplasts of oat

Adenylate levels in chloroplasts, mitochondria and the cytosol of oat mesophyll protoplasts were determined under light and dark conditions, in the absence and presence of plasmalemma-permeable inhibitors of electron transfer and uncouplers of phosphorylation. This was achieved using a microgradient technique which allowed an integrated homogenization and fractionation of protoplasts within 60 s (Hampp et al. 1982, Plant Physiol. 69, 448–455), under conditions which quench bulk activities of metabolic interconversion in less than 2 s. In illuminated controls, ATP/ADP ratios were found to be 2.1 in chloroplasts, about unity in mitochondria, and 11 in the cytosol; whereas, in the dark, this ratio only showed a large drop in chloroplasts (0.4). None of the compounds used [carbonylcyanide m-chlorophenylhydrazone (CCCP), carbonylcyanide p-trifluoromethoxy-phenylhydrazone (FCCP), antimycin A, dibromothymoquinone (DBMIB), dichlorophenyldi-methylurea (DCMU), or salicylhydroxamic acid (SHAM)] affected the stroma adenylate ratio in the dark. Under illumination, however, the ATP/ADP ratios were partly reduced in the presence of antimycin (inhibitor of cyclic photophosphorylation) and of DCMU (inhibitor of linear electron flow), while in the presence of DBMIB, DCMU+ antimycin (inhibition of both cyclic and linear electron flow), and CCCP (uncoupling) the ratio obtained was the same as that occurring in the dark. In contrast, mitochondrial adenylate levels did not exhibit large variations under the various treatments. The cytosolic ATP/ADP ratio, however, showed dramatic changes: in darkened protoplasts, cytosolic values dropped to 0.2 and 0.1 in the presence of uncouplers and antimycin, respectively, while SHAM did not induce any significant alteration. In the light, a similar pronounced decrease in ATP levels was observed only after the application of uncouplers or inhibitors of both mitochondrial and photosynthetic electron transport, whereas selective inhibition of the latter was largely ineffective in reducing the cytosolic ATP/ADP ratio. Thus, the results show that the antimycin-sensitive electron transport is, potentially, equally active in light and darkness. In addition, they indicate that antimycin-insensitive electron transport in mitochondria (alternative pathway) does not significantly contribute to the cytosolic energy state.Abbreviations CCCP carbonylcyanide m-chlorophenylhydrazone - DBMIB dibromothymoquinone (2,5-dibromo-3-methyl-6-isopropy-p-benzoquinone) - DCMU dichlorophenyldimethylurea - FCCP carbonylcyanide-p-trifluoromethoxy-phenylhydrazone - SHAM sancylhydroxamic acid     

Effects of dibromothymoquinone on mung bean mitochondrial electron transfer and membrane fluidity

The effects of the quinone analog dibromothymoquinone on electron transfer in isolated mung bean mitochondria are described. Both the main, cyanidesensitive and the alternate, cyanide-insensitive pathways are inhibited by dibromothymoquinone but in markedly different fashions. Half-maximal inhibition appeared at 40 μM and 20 μM dibromothymoquinone for the cyanide-sensitive and alternate pathways, respectively. With succinate as the electron donor, dibromothymoquinone inhibited the alternate pathway at a single site; showing a mixed, non-competitive type inhibition. On the succinate, cyanide-sensitive pathway dibromothymoquinone showed two sites of inhibition and neither coincides with the site of inhibition associated with the alternate pathway. With malate as the electron donor, two sites of inhibition by dibromothymoquinone were observed regardless of the pathway measured.Dibromothymoquinone also inhibited the rate of valinomycin-induced swelling of isolated mung bean mitochondria. Steady-state kinetics showed the inhibition to be non-competitive with respect to valinomycin. Additionally dibromothymoquinone was observed to increase the fluorescence polarization associated with the hydrophobic probe 1,6-diphenylhexatriene. The results indicated that dibromothymoquinone decreased the fluidity of the inner mitochondrial membrane and suggested that the inhibition of mitochondrial electron transfer by dibromothymoquinone may be associated with this decrease in membrane fluidity.The relationship of the multisite nature of the inhibition of electron transfer by dibromothymoquinone and the possible role of mobile electron carriers such as ubiquinone on the main and alternate respiratory pathways of higher plants is discussed.