Measurement of the extent of electron transfer to the bacteriopheophytin in the M-subunit in reaction centers of Rhodopseudomonas viridis

We have measured the extent of flash-induced electron transfer from the bacteriochlorophyll dimer, P, to the bacteriopheophytin in the M-subunit, H_M, in reaction centers of Rhodopseudomonas viridis. This has been done by measuring the transient states produced by excitation of reaction centers trapped in the PH_L ^–H_M state at 90 K. Under these conditions the normal forward electron transfer to the bacteriopheophytin in the L-subunit, H_L, is blocked and the yield of transient P⁺H_M ^– can be estimated with respect to the lifetime of P^*. Under these conditions flash induced absorbance decreases of the bacteriochlorophyll dimer 990 nm band suggest that a transient P⁺ state is formed with a quantum yield of 0.09±0.06 compared to that formed during normal photochemistry. These transient measurements provide an upper limited on the yield of a transient P⁺ H_M ^– state. An estimate of 0.09 as the yield of the P⁺ H_M ^– state is consistent with all current observations. This estimate and the lifetime of P^* suggest that the electron transfer rate from P^* to H_M, k_M, is about 5 × 10⁹ sec^–1 (_M = 200ps). These measurements suggest that the a branching ratio k_L/k_M is on the order of 200. The large value of the branching ratio is remarkable in view of the structural symmetry of the reaction center. This measurement should be useful for electron transfer calculations based upon the reaction center structure.     

Soil N mineralization and nitrification in relation to nitrogen solution chemistry in a small forested watershed

Spatial variations in soil processes regulating mineral N losses to streams were studied in a small watershed near Toronto, Ontario. Annual net N mineralization in the 0–8 cm soil was measured in adjacent upland and riparian forest stands using in situ soil incubations from April 1985 to 1987. Mean annual rates of soil N mineralization and nitrification were higher in a maple soil (93.8 and 87.0 kg.ha^–1) than in a pine soil (23.3 and 8.2 kg.ha^–1 ). Very low mean rates of mineralization (3.3 kg.ha^–1) and nitrification (3.4 kg.ha^–1) were found in a riparian hemlock stand. Average NO₃-N concentrations in soil solutions were 0.3–1.0 mg.L^–1 in the maple stand and >0.06mg.L^–1 in the pine stand. Concentrations of NO₃–N in shallow ground water and stream water were 3–4× greater in a maple subwatershed than in a pine subwatershed. Rapid N uptake by vegetation was an important mechanism reducing solution losses of NO₃–N in the maple stand. Low rates of nitrification were mainly responsible for negligible NO₃–N solution losses in the pine stand.     

Fructose production by Zymomonas mobilis in fed-batch culture with minimal sorbitol formation

Summary Fed-batch cultures of Zymomonas mobilis (UQM 2864), a mutant unable to metabolise fructose, grown on diluted sugar cane syrup (200 g/l sucrose) achieved yields of 90.5 g/l fructose and 48.3 g/l ethanol with minimal sorbitol formation and complete utilization of the substrate. The effect of inoculum size on sorbitol formation in the batch stage of fed-batch fermentation are reported. Fermentation of sucrose (350 g/l) supplemented with nutrients yielded 142 g/l fructose and 76.5 g/l ethanol. Some fructose product loss at high fructose concentrations was observed. The fed-batch fermentation process offers a method for obtaining high concentrations of fructose and ethanol from sucrose materials.     

Isoenzyme pattern and subcellular localisation of enzymes involved in fumaric acid accumulation by Rhizopus oryzae

Summary Electrophoretic studies of fumarase and nicotine adenine dinucleotide (NAD)-malate dehydrogenase were carried out in the fumaric acid-accumulating fungus Rhizopus oryzae. The analyses revealed two fumarase isoenzymes, one localised solely in the cytosol and the other found both in the cytosol and in the mitochondrial fraction. The activity of the cytosolic isoenzyme of fumarase was higher during the acid production stage than during growth. Addition of cycloheximide inhibited fumaric acid production and decreased the activity of the cytosolic isoenzyme of fumarase. These results suggested that de novo protein synthesis is required for increase in the activity of the cytosolic isoenzyme and that such an increase in activity is essential for fumaric acid accumulation. Three distinct isoenzymes of NAD-malate dehydrogenase could be detected in R. oryzae. No changes were observed in the isoenzyme pattern of malate dehydrogenase during fumaric acid production.     

Inhibition of isoproterenol-induced DNA and RNA synthesis in rat parotid and pancreas following removal of submandibular-sublingual glands

Summary [³H] thymidine incorporation into DNA of the parotid (PA) gland of adult and 20-day-old rats and into DNA of the pancreas (PANC) of 20-day-old rats was increased markedly following a 2-day regimen of isoproterenol (ISO) administration. However, when the submandibular-sublingual (SM-SL) glands had been removed just prior to initiation of the ISO injections, the [³H] thymidine incorporation into PA and PANC was inhibited, and cpm/mg protein of these organs was even lower than that of organs of untreated rats with SM-SL glands present. Removal of the PA glands just prior to initiation of the ISO regimen had no effect on the ISO-induced [³H] thymidine incorporation into DNA of PANC but partially inhibited that of the submandibular (SM) gland. It is suggested that the inhibitory effects on DNA and RNA synthesis that follow removal of SM-SL glands are attributable to the growth factors (epidermal growth factor and nerve growth factor) found in the rat SM gland. These factors appear to regulate normal DNA synthetic activity of exocrine glands as well as ₁-adrenoceptor mediated DNA synthesis. Cellular hypertrophy induced by the ISO was less markedly affected by absence of the SM glands, but a partial inhibition of [³H] uridine incorporation into RNA of PA of adult rats also occurred when SM-SL glands were removed prior to initiation of the ISO-regimen.     

Appearance of lectin-binding sites during vascularization of the primordium of the central nervous system in 10 to 12-day-old mouse embryos

Summary In the present study lectin-binding sites were investigated for the lectins Ricinus communis agglutinin (RCA I), wheat germ agglutinin (WGA), soya bean agglutinin (SBA), concanavalin A (Con A), Lotus tetragonolobus(LTA) and Limulus polyphemus agglutinin (LPA) during the initial stages of vasculogenesis of the CNS-anlage in 10 to 12-day-old NMRI mouse embryos. Specific binding sites for the lectins RCA I (sugar specificity: -D-galactose, N-acetylgalactosamine), WGA (sugar specificity: N-acetylglucosamine, sialic acid), and SBA (sugar specificity: N-acetylgalactosamine, -D-galactose) were detected in the newly formed capillaries within the neuroepithelial cell layer. In contrast, binding sites for Con A, LTA and LPA could not be observed at the start of the vascularization of the CNS-anlage. From these results, the conclusion can be drawn that glycoconjugates containing D-galactose, N-acetylgalactosamine and N-acetyl-glucosamine moieties are involved in the early vasculogenesis of the embryonic CNS-anlage of the mouse.     

Carbonic anhydrase activity in acetate grown Methanosarcina barkeri

Cell extracts (27000xg supernatant) of acetate grown Methanosarcina barkeri were found to have carbonic anhydrase activity (0.41 U/mg protein), which was lost upon heating or incubation with proteinase K. The activity was inhibited by Diamox (apparent K _i=0.5 mM), by azide (apparent K _i=1 mM), and by cyanide (apparent K _i=0.02 mM). These and other properties indicate that the archaebacterium contains the enzyme carbonic anhydrase (EC 4.2.1.1). Evidence is presented that the protein is probably located in the cytoplasm. Methanol or H₂/CO₂ grown cells of M. barkeri showed no or only very little carbonic anhydrase activity. After transfer of these cells to acetate medium the activity was induced suggesting a function of this enzyme in acetate fermentation to CO₂ and CH₄. Interestingly, Desulfobacter postgatei and Desulfotomaculum acetoxidans, which oxidize acetate to 2 CO₂ with sulfate as electron acceptor, were also found to exhibit carbonic anhydrase activity (0.2 U/mg protein).     

Immunohistochemical investigation of different cytokeratins and vimentin in the human epididymis from the fetal period up to adulthood

Summary The anatomical distribution of cytokeratins and vimentin was investigated by means of immunohistochemistry in the human epididymis. Epithelial cells of the ductuli efferentes and the corpus epididymidis were positive for cytokeratins and vimentin. The expression of epithelial vimentin decreased toward the cauda epididymidis, whereas cytokeratins remained unchanged. The epithelium of the ductus deferens was negative when antibodies against vimentin were used. With monoclonal antibodies to individual cytokeratins, the presence of cytokeratins 7, 8, 18, and 19 was demonstrated histochemically throughout the epithelium of the epididymis. Monoclonal antibodies specific for cytokeratin 17 allowed immunohistochemical differentiation between the ductuli efferentes and the ductus epididymidis.