The Compatibility of d-Pinitol and 1d-1-O-Methyl-Muco-Inositol with Malate Dehydrogenase Activity

Pinitol (1d -3-O-methyl-chiro-inositol) and 1d -1-O-methyl-muco-inositol, two cyclitols wide-spread in the plant kingdom, were isolated from plant sources in order to test their compatibility with malate dehydrogenase activity. Both compounds had no inhibitory effect on malate dehydrogenase from Rhizophora mangle in a range of 100 to 1000 mol . m^?3. Their influence on malate dehydrogenase activity from different plant sources (Rh. mangle L., Mesembryanthemum crystallinum L., Cicer arietinum L. and Spinacia oleracea L.) was also small and similar to that observed for a number of well established compatible solutes (e.g. proline, glycine betaine). A possible role of cyclitols as cryoprotectants or radical scavengers is discussed.     

Thiol-induced oligomerization of α-lactalbumin at high pressure

Denaturation and aggregation of-lactalbumin at high pressure (up to 10 kbar, 1000 MPa) were studied by means of circular dichroism, gel-permeation chromatography, sodium dodecyl sulfate and gel electrophoresis. It was found that the unfolding of-lactalbumin at high pressure is reversible even in basic pH and at a protein concentration as large as 10%. In these conditions only a negligible fraction of the protein is denatured irreversibly and aggregates. The rate of aggregation of-lactalbumin at high pressure increases significantly in the presence of low-molecular reducing agents such as cysteine, 2-mercaptoethanol, and dithiothreitol. Maximal yield of-lactalbumin oligomerization (over 90%) was achieved in the presence of cysteine at the molar cysteine/protein ratioq=2 and atpH 8.5. Apparent molecular weight of the obtained oligomers was over 500 kDa. It was shown that the size distribution of oligomers can be modulated by varyingpH and reducing agent. The size distribution shifts in the direction of very large, poorly soluble particles whenpH decreases. Maximal content of the insoluble fraction (about 30%) can be reached at pH 5.5 when cysteine (q=2) is used as reducing agent. The oligomers of-lactalbumin are stabilized mainly by nonnative interchain disulfide bridges. Circular dichroism measurements point to an additional mechanism of cohesion of polypeptide chains in the oligomers, which is formation of intermolecular-sheets.     

Determination of 4,4′-methylenediphenyldianiline (MDA) and identification of isomers in technical-grade MDA in hydrolysed plasma and urine from workers exposed to methylene diphenyldiisocyanate by gas chromatography-mass spectrometry

Gas chromatography-mass spectrometry using chemical ionization with ammonia as reagent gas monitoring both positive and negative ions was applied. Negative-ion monitoring using ammonia and the pentafluoropropionic anhydride (PFPA) derivatives were chosen owing to low detection limits and good separation for the isomers studied. Technical-grade methylenediphenyldiioscyanate (MDI) was analysed and three isomers, 4,4′−, 2.4′− and 2,2−methylenediphenyldianiline (MDA), were determined in addition to methylated MDA. Plasma and urine from an exposed worker were hydrolysed and analysed and the MDA isomers were identified in the biological samples.     

Brefeldin a down-regulates the transferrin receptor in K562 cells

The fungal metabolite brefeldin A (BFA) induces profound alterations in the morphology of intracellular organelles. Although BFA promotes the formation of extensive tubular endosomal domains, our understanding of the effects of the antibiotic on vesicle traffic events associated with endocytosis is limited. Thus, alterations in the transferrin (Tf) receptor's endocytic/recycling pathway upon treatment of human erythroleukemia K562 cells with BFA were studied as a pharmacological response. Treatment of K562 cells with BFA caused a down-regulation in the number of cell surface Tf receptors. This effect is highly reminiscent of the well-known action of phorbol 12-myristate 13-acetate (PMA) on Tf receptor traffic in K562 cells. However, our results demonstrate that these two agents down-regulate the Tf receptor via different mechanisms. The effects of BFA and PMA were additive when K562 cells were incubated with both together. Using the In/Sur method, the endocytic rate constant for Tf internalization was determined and PMA was found to greatly enhance k_e, from 0.28 min^–1 to 0.43 min^–1, while BFA had little effect (K_e=0.20 min^–1). In contrast, BFA-treatment alters the exocytic rate constant for return of internalized receptors to the cell surface, with the largest effect exerted on a slow-release, monensin-sensitive, compartment. The sum of the endocytic and exocytic kinetic data support a model in which BFA and PMA down-regulate the Tf receptor in K562 cells by mechanistically distinct actions, with BFA targeting exocytic monensin-sensitive intracellular compartments and PMA acting to exert a profound influence on elements of receptor internalization.Abbreviations BFA brefeldin A - ARF ADP-ribosylation factor - HRP horseradish peroxidase - Tf transferrin - PMA phorbol 12-myristate 13-acetate - DMSO dimethyl sulfoxide - PBS phosphate-buffered saline - HEPES 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - BSA bovine serum albumin - FITC-Tf fluorescein isothiocyanate-labelled transferrin     

Biogeochemical cycling of sulfur and iron in sediments of a south-east Asian mangrove,Phuket Island,Thailand

Benthic sulfate reduction and sediment pools of sulfur and iron were examined during January 1992 at 3 stations in the Ao Nam Bor mangrove, Phuket, Thailand. Patterns of sulfate reduction rates (0–53 cm) reflected differences in physical and biological conditions at the 3 stations, and highest rates were found at the vegetated site within the mangrove (Rhizophora apiculata) forest. Due to extended oxidation of mangrove sediments, a large portion of the added³⁵S-label was recovered in the chromium reducible pools (FeS₂ and S⁰) (41–91% of the reduced sulfur). Pyrite was the most important inorganic sulfur component, attaining pool sizes 50–100 times higher than acid volatile pools (FeS). HCl-extractable (0.5 M HCl) iron pools, including Fe(II)_HCl and Fe(III)_HCl, were generally low and Fe(III)_HCl was only present in the upper surface layers (0–5 cm). Maximum concentrations of dissolved Fe²⁺ (35–285 M) occurred just about the depth where dissolved H₂S accumulated. Furthermore Fe²⁺ and H₂S coexisted only where concentrations of both were low. There was an accumulation of organic sulfur in the deep sediment at 2 stations in the inner part of the mangrove. The reoxidation of reduced sulfides was rapid, and storage of sulfur was minor in the upper sediment layers, where factors like bioturbation, the presence of roots, or tidal mixing enhance oxidation processes.Author of correspondence.     

Fine root growth phenology,production, and turnover in a northern hardwood forest ecosystem

A large part of the nutrient flux in deciduous forests is through fine root turnover, yet this process is seldom measured. As part of a nutrient cycling study, fine root dynamics were studied for two years at Huntington Forest in the Adirondack Mountain region of New York, USA. Root growth phenology was characterized using field rhizotrons, three methods were used to estimate fine root production, two methods were used to estimate fine root mortality, and decomposition was estimated using the buried bag technique. During both 1986 and 1987, fine root elongation began in early April, peaked during July and August, and nearly ceased by mid-October. Mean fine root ( 3 mm diameter) biomass in the surface 28-cm was 2.5 t ha^–1 and necromass was 2.9 t ha^–1. Annual decomposition rates ranged from 17 to 30% beneath the litter and 27 to 52% at a depth of 10 cm. Depending on the method used for estimation, fine root production ranged from 2.0 to 2.9 t ha^–1, mortality ranged from 1.8 to 3.7 t ha^–1 yr^–1, and decomposition was 0.9 t ha^–1 yr^–1. Thus, turnover ranged from 0.8 to 1.2 yr^–1. The nutrients that cycled through fine roots annually were 4.5–6.1 kg Ca, 1.1–1.4 kg Mg, 0.3–0.4 kg K, 1.2–1.7 kg P, 20.3–27.3 kg N, and 1.8–2.4 kg S ha^–1. Fine root turnover was less important than leaf litterfall in the cycling of Ca and Mg and was similar to leaf litterfall in the amount of N, P, K and S cycled.     

394delTT: a Nordic cystic fibrosis mutation

In a systematic screening for mutations in the gene encoding the cystic fibrosis transmembrane regulator among Danish cystic fibrosis (CF) patients, we identified a mutation in exon 3 (394delTT); this mutation was found to be relatively common in Denmark. We therefore screened for 394delTT in Sweden and Norway, where it turned out to be the second most frequent mutation, accounting for 4% of all CF mutations. It also occurs with a high frequency in Finland, but has not been found in larger surveys of mutations in the CFTR gene. Thus, 394delTT seems to be a specific Nordic CF mutation.     

Synergism of Trichoderma reesei cellulases while degrading different celluloses

Summary The synergistic action of purified cellulases from Trichoderma reesei in hydrolysis of cellulose decreased with increasing substrate concentration, depended strongly on the the type of cellulose used, and was maximal on crystalline cellulose. Contrarily, the activity of the individual cellulases was highest on amorphous cellulose. The binary combinations CBH I/EG III and CBH I/CBH II exhibited the greatest degree of synergism on crystalline cellulose.     

Extracellular targeting of the vacuolar tobacco proteins AP24, chitinase and β-1,3-glucanase in transgenic plants

The Nicotiana tabacum ap24 gene encoding a protein with antifungal activity toward Phytophthora infestans has been characterized. Analysis of cDNA clones revealed that at least three ap24-like genes are induced in tobacco upon infection with tobacco mosaic virus. Amino acid sequencing of the purified protein showed that AP24 is synthesized as a preproprotein from which an amino-terminal signal peptide and a carboxyl-terminal propeptide (CTPP) are cleaved off during post-translational processing. The functional role of the CTPP was investigated by expressing chimeric genes encoding either wild-type AP24 or a mutant protein lacking the CTPP. Plants expressing the wild-type construct resulted in proteins properly sorted to the vacuole. In contrast, the proteins produced in plants expressing the mutant construct were secreted extracellularly, indicating that the CTPP is necessary for targeting of AP24 to the vacuoles. Similar results were obtained for vacuolar chitinases and -1,3-glucanases of tobacco. The extracellularly targeted mutant proteins were shown to have retained their biological activity. Together, these results suggest that within all vacuolar pathogenesis-related proteins the targeting information resides in a short carboxyl-terminal propeptide which is removed during or after transport to the plant vacuole.