A plant protein kinase and plant microsomal H+ transport are stimulated by the ether phospholipid platelet-activating factor

ATP-dependent H⁺ transport in microsomes from zucchini hypocotyls is stimulated by the ether lipid 1-0-alkyl-2-acetyl-sn-glycero-3-phosphocholine (platelet-activating factor = PAF) known as a hormone-like substance from mammals. The stimulation can only be observed when soluble cytosolic proteins are present. A soluble protein mediating the PAF-dependent H⁺ transport and a PAF-stimulated protein kinase are coeluted by DEAE-Sephacel chromatography. Stimulation of phosphorylation by PAF of a 55 kDa polypeptide without Ca²⁺ and, additionally, of a 35 kDa polypeptide in the presence of Ca²⁺ is observed in zucchini microsomal membranes. This is evidence for a novel phospholipid-stimulated protein kinase in plants. Phosphorylation of regulatory proteins may be involved in the stimulation of in vitro H⁺ transport by PAF.Abbreviations BTP 1,3-bis (tris(hydroxymethyl)-methylamino) propane - DTT dithiotreitol - EGTA ethylene glycol-bis (ß-aminoethyl ether)-N,N,N,N,-tetraacetic acid - Mes 2-(N-morpholino) ethanesulfonic acid - PAF platelet-activating factor = 1-0-alkyl-2-acetyl-sn-glycero-3-phosphocholine - SDS sodium dodecylsulfate - TCA trichloroacetic acid     

Theβ-subunit of human chorionic gonadotropin containsN-glycosidic trisialo tri- and tri′-antennary carbohydrate chains

TheN-linked carbohydrate chains of the-subunit of highly purified urinary human chorionic gonadotropin have been re-investigated. The oligosaccharides were released enzymatically by peptide-N ⁴-(N-acetyl--glucosaminyl)asparagine amidase-F, and fractionated by a combination of FPLC and HPLC. As a result of the application of improved fractionation methods, apart from the earlier reported carbohydrate chains, also small amounts of trisialo tri- and tri-antennary oligosaccharides were found. The primary structures of the latter carbohydrate chains have been determined by 500-MHz¹H-NMR spectroscopy to beAbbreviations hCG human chorionic gonadotropin - hCG- -subunit - hCG- -subunit - PNGase-F peptide-N ⁴-(N-acetyl--glucosaminyl)asparagine amidase-F (E.C. 3.5.1.52) - endo-F endo--N-acetylglucosaminidase-F (E.C. 3.2.1.96) - SDS sodium dodecyl sulphate - PAGE polyacrylamide gel electrophoresis - CBB coomassie brilliant blue R 250 - GlcNAc N-acetylglucosamine - NeuAc N-acetylneuraminic acid - Man mannose - Gal galactose - Fuc fucose     

Stimulation of phospholipase A2 by auxin in microsomes from suspension-cultured soybean cells is receptor-mediated and influenced by nucleotides

The molecular mechanism of membrane-associated reactions induced by auxin was investigated in membranes isolated from cultured cells of soybean (Glycine max L.). Auxins increased the activity of phospholipase A₂ in microsomes isolated from suspensioncultured soybean cells. The reaction was measured as the accumulation of radioactive lysophosphatidylcholine hydrolyzed from radioactive phosphatidylcholine in membranes which had been prelabelled with [¹⁴-C]choline in vivo. Stimulation by auxin was detectable after 1 min and was auxin-specific in that weak auxins had little effect. Auxin concentrations as low as 2·10^–8 M and up to 2·10⁺³ M -naphthaleneacetic acid already stimulated the phospholipase A₂ activity. Guanosine and adenosine diphosphate at 100 M, if applied during homogenization of cells, completely abolished the stimulation of phospholipase A₂ by auxin and, when applied after homogenization, had no effect. Guanosine and adenosine 5-O-thiotriphosphate, uridine 5-diphosphate, and uridine 5-triphosphate, all at 100 M, had no effect in either treatment, suggesting that only nucleotides entrapped in the vesicles could exert an effect. The effect of auxin on phospholipase A₂ had an optimum at pH 5.5 and was abolished completely by an antibody against the membrane-associated auxin-binding protein from maize coleoptiles, applied after homogenization. This antibody recognized a 22-kDa polypeptide in highly purified plasma membranes from cultured soybean cells. This suggests a receptor function for this auxin-binding protein and a role for a cytosolic nucleotide-binding protein in the activation of phospholipase A₂ by auxin. It is concluded that phospholipase A₂ has a function in plant signal transduction.Abbreviations ABP auxin-binding protein - ATP S adenosine 5-O-thiotriphosphate - 2,4-D 2,4-dichlorophenoxyacetic acid - GTP S guanosine 5-O-(thiotriphosphate) - IgG immunoglobulin G - LPC lysophosphatidylcholine; - -NAA , -naphthaleneacetic acid - PLA₂ phospholipase A₂ We cordially acknowledge the gift of anti-ABP antibody by D. Klämbt and the help by H. Ordowski (both Botanisches Institut, Universität Bonn) with the immunoblotting experiments. This work was supported by the Deutsche Forschungsgemeinschaft.     

A survey of the response of Rhododendron to in vitro culture

The responses of 7 genotypes of Rhodendron to culture conditions and their establishment as shoot cultures are described. The genotypes represent a broad genetic diversity in the genus. After sterilization and an acclimation period of 3 to 12 months, all the selections were established as shoot cultures on Woody Plant Medium (WPM) supplemented with N⁶(-²-isopenteny) adenine (2iP). Plants with strong episodic growth cycles required the longer acclimation periods. Utilizing shoots from these cultures, the response to a cytokinin series of 0 to 32 M 2iP or BAP (6-Benzylaminopurine) was analyzed. BAP proved toxic to all but the elipidote and lepidote rhododendrons (R. mucronulatum, R. x Boule de Neige, and R. x PJM); however, even with these selections, 2iP stimulated greater shoot multiplication rates. The optimum 2iP level for shoot multiplication varied little with the genotype and levels of 4 to 16 M generally proved optimal, depending on the specific selection. Adventitious shoot production was observed in 3 selections (R. canadense, R. x Boule de Neige and R. x PJM), but only at 2iP levels above 8 M. Shoot multiplication rates of 7 to 21 times were observed, depending on the selection. Using an average utilizable shoot production rate of 40 shoots per culture per 6 week subculture period, some 75,000 shoots can be generated per square meter of culture space per year. The harvested shoots (microcuttings) rooted readily out-of-culture and the resultant plants grew like seedlings.     

Association of gangliosides to fibroblasts in culture: A study performed with GM1 [14C]-labelled at the sialic acid acetyl group

The preparation of a G_M1-ganglioside (GM1) [¹⁴C]-labelled in the sialic acid residue is reported. This can be obtained by re-N-acetylation in the presence of [1-¹⁴C]-acetic anhydride, of a GM1 derivative de-N-acetylated specifically on the sialic acid residue by alkaline hydrolysis of GM1 with tetramethylammonium hydroxide. The radiolabelled GM1 is utilized to investigate the binding properties and the mode of interaction of GM1 with cultured fibroblasts. Three different forms of association (one serum-removable, one trypsin-removable and one trypsin-stable) have been recognized to occur in a way that depended on cell culture conditions (presence or absence of fetal calf serum), ganglioside concentration (from, 5×10^–9 M to 10^–4 M) and incubation time (up to 24 h). Some metabolic modifications of GM1 during the period of high cell viability were also investigated.Abbreviations GM1 G_M1-ganglioside, II³NeuAc-GgOse₄Cer - FCS fetal calf serum - EMEM Eaglés Minimum Essential Medium with Earlés salts - PBS Dulbecco phosphate buffered saline without calcium and magnesium     

Basis of the Relationship between Ash Content in the Flag Leaf and Carbon Isotope Discrimination in Kernels of Durum Wheat

The relationship between ash content and carbon isotope discrimination () was studied in durum wheat (Triticum durum Desf.) grown in a Mediterranean region (Northwest Syria) under three different water regimes (hereafter referred to as environments). In two of these environments, 144 genotypes were cultivated under rain-fed conditions. In the third environment, 125 genotypes were cultivated under irrigation. Ash content was measured in the flag leaf about 3 weeks after anthesis, whereas was analysed in mature kernels. Total transpiration of the photosynthetic tissues of the culm contributing, from heading to maturity, to the filling of kernels was also estimated. Leaf ash content, expressed either on dry matter or leaf area basis or as total ash per blade, correlated positively (p< 0.001) with in the three environments. However, this relationship was not the result of a positive correlation across genotypes between and tissue water content. Moreover, only a small part of the variation in across genotypes was explained by concomitant changes in ash content. When all genotypes across the three environments were plotted, and ash content followed a non-linear relationship (r ² = 74), with tending to a plateau as the ash content increased. However, for the set of genotypes and environments combined, total ash content per leaf blade was positively and linearly related (r ² = 0.76) with the accumulated culm transpiration. The non-linear nature of the relationship between ash content and is sustained by the fact that culm transpiration also showed a non-linear relationship with kernel . Therefore, differences in leaf ash content between environments, and to a lesser extent between genotypes, seem to be brought about by variations in accumulated transpiration during grain formation.     

Effects of G-protein probes on interactions between auxin efflux carriers and phytotropin receptors in zucchini (Cucurbita pepo L.) microsomal membranes

Microsomal vesicles prepared from etiolated hypocotyl tissue of zucchini (Cucurbita pepo L. cv. All Green Bush) exhibited saturable N-1-naphthylphthalamic acid ([³H]NPA) binding, NPA-stimulated association of indol-3yl-acetic acid ([³H]IAA), and saturable binding of guanosine 5-O-[3-thiotriphosphate] (GTP--[³⁵S]). These vesicles were used to test the possibility that NPA receptors might interact with IAA-anion efflux carriers by coupling through a GTP-binding protein (G-protein). Unlabelled GTP--S or guanosine 5-O-[2-thiodiphosphate] (GDP--S) had no effect on saturable NPA binding or on the NPA-stimulated association of IAA with microsomes. NPA did not affect saturable binding of GTP--[³⁵S] to microsomes, either in the presence or absence of saturating concentrations of unlabelled GTP--S or GDP. It is concluded that the occupancy of phytotropin receptors is not transduced to auxin efflux carriers by a GTP-binding protein.     

Calcium-dependent protein kinase from apple fruit membranes is calmodulin-independent but has calmodulin-like properties

Crude Ca²⁺-activated protein kinase from membranes of apple (Malus domestica L. Borkh., Cox's Orange Pippin) fruit can be partially purified to yield a Ca²⁺-dependent protein kinase whose activity is apparently not regulated by calmodulin. The autophosphorylating catalytic subunit of this protein kinase shows a Ca²⁺-dependent mobility shift of approx. 10 kilodaltons (kDa) on sodium dodecyl sulphate-polyacrylamide gel electrophoresis; in the absence of added Ca²⁺ or ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid (EGTA) its apparent molecular mass is approx. 50 kDa. The Ca²⁺-dependent protein kinase is inhibited by the calmodulin antagonists N-(6-aminohexyl)-5-chloro-1-naphthalenesulphonamide and trifluoperazine with IC₅₀ values of approx. 45 M and 15 M, respectively. These similarities between the protein kinase and calmodulin indicate that the kinase may be a calmodulin-like protein.Abbreviations DEAE diethylaminoethyl - EGTA ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid - Hepes 4-(-2-hydroxyethyl)-1-piperazineethanesulphonic acid - kDa kilodalton - PAGE polyacrylamide gel electrophoresis - SDS sodium dodecyl sulphate - W7 N-(6-aminohexyl)-5-chloro-1-naphthalenesulphonamide - W5 N-(6-aminohexyl)-naphthalenesulphonamide     

Regulation of pH in the isolated perfused gills of the shore crabCarcinus maenas

Isolated posterior gills (no. 7) of shore crabsCarcinus maenas acclimated to brackish water of a salinity of 10 S were bathed and perfused with 50% sea water (200 mmol·l^-1 Na⁺), and the internal perfusate collected during subsequent periods of 5 min. During a single passage through the gill the pH of the perfusion medium decreased from ca. 8.1 to ca. 7.7, a result implying that the gill possesses structures which recognize unphysiologically high pH values in the haemolymph and regulates them down to physiological values of ca. 7.7. The calculated apparent proton fluxes from the epithelial cells into the haemolymph space amounted to 17.9 mol·g fw^-1·h^-1, a value of only 3.8% of net Na⁺ fluxes observed under comparable conditions. When 0.1 mmol·l^-1 KCN, an inhibitor of mitochondrial cytochrome oxidase, or 5 mmol·l^-1 ouabain, a specific inhibitor of Na⁺/K⁺-ATPase were applied in the internal perfusate, down-regulation of pH was no longer observed and the gill was completely depolarized, i.e. transepithelial potential differences dropped from-7.8 to 0 mV (haemolymph space negative to bath). Regulation of pH was completely inhibited by antagonists of carbonic anhydrase (0.1 mmol·l^-1 acetazolamide or 0.01 mmol·l^-1 ethoxyzolamide) applied in the perfusate. Inhibitors of Na⁺/H⁺ exchange, 0.1 mmol·l^-1 amiloride applied in the external bathing medium or in the internal perfusate, and symmetrical 0.01 mmol·l^-1 5-(N-ethyl-N-isopropyl)amiloride, as well as inhibitors of Cl^-/HCO₃ ^- exchange and Na⁺/HCO₃ ^- cotransport, 0.5 mmol·l^-1 4,4-diisothiocyanatostilbene-2,2-disulphonate or 0.3 mmol·l^-1 4-acetamido-4-isothiocyanatostilbene 2,2-disulphonate applied on both sides of the gill, and inhibitors of H⁺-ATPase, 0.05 mmol·l^-1 N-ethylmaleimide and 0.1 mmol·l^-1 N,N-dicyclohexylcarbodiimide —applied on both sides of the gill — did not alter the acidification of the perfusate observed in controls. Using artificial salines buffered to pH 8.1 with 0.75 mmol·l^-1 tris (hydroxymethyl) aminomethane instead of 2 mmol·l^-1 HCO₃ ^-, apparent proton fluxes were reduced to 11% of controls, a result suggesting that pH regulation by crab gills needs the presence of HCO₃ ^-. The findings obtained suggest that pH regulation by crab gills depends on the oxidative metabolism of the intact branchial epithelium and that carbonic anhydrase plays a central role in this process. Na⁺/H⁺ exchange, anion exchange or cotransport and active proton secretion seem not to be involved. While unimpaired active ion uptake is a prerequisite for pH regulation, ion transport itself is independent of it.Abbreviations acetazolamide (N-[sulphamoyl-1, 3, 4-thiadiazol-2-yl]-acetamide) - amiloride 3,5-diamino-6-chloropyrazinoyl-guanidine - CA carbonic anhydrase - DBI dextrane-bound inhibitor thiadiazolesulphonamide - DCCD N N dicyclohexylcarbodiimide - DIDS 4,4-diisothiocyanato-stilbene-2,2-disulphonate - EIPA 5-(N-ethyl-N-isopropyl) amiloride - ethoxyzolamide 6-ethoxy-2-benzothiazole-sulphonamide - fw fresh weight - J _H ⁺ apparent proton flux - NEM N-ethylmaleimide - PD transepithelial potential difference - PEG-STZ polyethylene-glycol-thiadiazolesulphonamide - STTS 4-acetamido-4-isothiocyanatostibene 2,2-disulphonate - SW sea water - TRIS tris(hydroxymethyl)aminomethane     

Calcium transport by pea root membranes

Calcium transport has been studied using purified endomembrane vesicles from dark-grown roots of Pisum sativum L. Membranes from a mixed microsomal (non-mitochondrial) fraction showed ATP-dependent calcium uptake which was released by the ionophore A 23187, had a pH optimum of 7.2 and required Mg²⁺ for uptake. Membranes were further purified using a rapid sucrosedensity-gradient technique yielding vesicles suitable for transport studies, and were identified using marker enzymes. Uptake by plasma membrane, tonoplast, endoplasmic reticulum and Golgi apparatus was indicated. Uptake by membranes of low density (predominantly tonoplast) had a pH optimum of 7.2–7.4 and nucleotide specificity ATP> guanosine 5-triphosphate>inosine 5-triphosphate>ADP>, while that by high-density membranes had a pH optimum of 7.5–7.9 and less specificity for ATP. The importance of regulating sucrose concentrations in calcium transport studies was demonstrated.Abbreviations ER endoplasmic reticulum - GTP guanosine 5-triphosphate - IDPase inosine diphosphatase - IIP inosine 5-triphosphate     

Modification of lignin by Geotrichum klebahnii

¹³C-NMR spectroscopic analysis indicates that the yeast-like species Geotrichum klebahnii is an efficient microorganism for lignin biodegradation. This strain modified beechwood lignin even if it was the only carbon source by C-C side chain cleavage, C-oxidations, aromatic ring cleavage and reductive reactions. The obtained results outline prospective application of G. klebahnii for biotechnological pre-treatment of lignocellulosic materials.     

Beta-Adrenergic modulation of K+ current in human T lymphocytes

Summary The whole-cell voltage-clamp technique was employed to study the -adrenergic modulation of voltage-gated K⁺ currents in CD8⁺ human peripheral blood lymphocytes. The -receptor agonist, isoproterenol, decreased the peak current amplitude and increased the rate of inactivation of the delayed rectifier K⁺ current. In addition, isoproterenol decreased the voltage dependence of steady-state inactivation and shifted the steady-state inactivation curve to the left. Isoproterenol, on the other hand, had no significant effect on the steady-state parameters of current activation. The isoproterenol-induced decrease in peak current amplitude was inhibited by the -blocker propranolol. Bath application of dibutyryl cAMP (1mm) mimicked the effects of isoproterenol on both K⁺ current amplitude and time course of inactivation. Furthermore, the reduction in the peak current amplitude in response to isoproterenol was attenuated when PKI_5–24 (2–5 m), a synthetic peptide inhibitor of cAMP-dependent protein kinase, was present in the pipette solution. The increase in the rate of inactivation of the K⁺ currents in response to isoproterenol was mimicked by the internal application of GTP--S (300 m) and by exposure of the cell to cholera toxin (1 g/ml), suggesting the involvement of a G protein. These results demonstrate that the voltage-dependent K⁺ conductance in T lymphocytes can be modulated by -adrenergic stimulation. The effects of -agonists, i.e., isoproterenol, appear to be receptor mediated and could involve cAMP-dependent protein kinase as well as G proteins. Since inhibition of the delayed rectifier K⁺ current has been found to decrease the proliferative response in T lymphocytes, the -adrenergic modulation of K⁺ current may well serve as a feedback control mechanism limiting the extent of cellular proliferation.     

Characterization of inside-out oriented H+-ATPases in cholate-pretreated renal brush-border membrane vesicles

Summary Exposure of porcine renal brush-border membrane vesicles to 1.2% cholate and subsequent detergent removal by dialysis reorients almost all N-ethylmaleimide (NEM)-sensitive ATPases from the vesicle inside to the outside. ATP addition to cholate-pretreated, but not to intact, vesicles causes H⁺ uptake as visualized by the pH indicator, acridine organge. The reoriented H⁺-pump is electrogenic because permeant extravesicular anions or intravesicular K⁺ plus valinomycin enhance H⁺ transport. ATP stimulates H⁺ uptake with an apparentK _m of 93 m. Support of H⁺ uptake andP _i liberation by ATP>GTPITP> UTP indicates a preference for ATP and utilization of other nucleotides at lower efficiency. ADP is a potent, competitive inhibitor of ATP-driven H⁺ uptake,(K _i , 24 m). Mg²⁺ and Mn^2– support ATP-driven H⁺ uptake, but Ca²⁺, Ba²⁺ and Zn²⁺ do not. Imm Zn²⁺ inhibits MgATP-driven H⁺ transport completely. NEM-sensitiveP _i liberation is stimulated by Mg²⁺ and Mg^2– and, unlike H⁺ uptake, also by Ca²⁺ suggesting Ca²⁺-dependent ATP hydrolysis unrelated to H⁺ transport. The inside-out oriented H⁺-pump is relatively insensitive toward oligomycin, azide, N,N-dicyclohexylcarbodiimide (DCCD) and vanadate, but efficiently inhibited by NEM (apparentK _i , 0.77 m), and 4-chloro-7-nitro-benzoxa-1,3-diazole (NBD-Cl; apparentK _i , 0.39 m). Taken together, the H⁺-ATPase of proximal tubular brush-border membranes exhibits characteristics very similar to those of vacuolar type (V-type) H⁺-ATPases. Hence,V-type H⁺-ATPases occur not only in intracellular organelles but also in specialized plasma membrane areas.     

ATP is required for K+ active transport in the archaebacterium Haloferax volcanii

The Archaebacterium Haloferax volcanii concentrates K⁺ up to 3.6 M. This creates a very large K⁺ ion gradient of between 500- to 1,000-fold across the cell membrane. H. volcanii cells can be partially depleted of their internal K⁺ but the residual K⁺ concentration cannot be lowered below 1.5 M. In these conditions, the cells retain the ability to take up potassium from the medium and to restore a high internal K⁺ concentration (3 to 3.2 M) via an energy dependent, active transport mechanism with a K _m of between 1 to 2 mM. The driving force for K⁺ transport has been explored. Internal K⁺ concentration is not in equilibrium with m suggesting that K⁺ transport cannot be accounted for by a passive uniport process. A requirement for ATP has been found. Indeed, the depletion of the ATP pool by arsenate or the inhibition of ATP synthesis by N,N-dicyclohexylcarbodiimide inhibits by 100% K⁺ transport even though membrane potential m is maintained under these conditions. By contrast, the necessity of a m for K⁺ accumulation has not yet been clearly demonstrated. K⁺ transport in H. volcanii can be compared with K⁺ transport via the Trk system in Escherichia coli.Abbreviations CCCP Carbonylcyanide m-chlorophenyl-hydrazone - DCCD N,N-dicyclohexylcarbodiimide - MES 2-[N-morpholino] ethane sulfonic acid - MOPS 3-[N-morpholino] propane sulfonic acid - TRIS Tris (hydroxymethyl) aminomethane - TPP tetraphenyl phosphonium     

A 500-MHz1H-NMR study on theN-linked carbohydrate chain of bromelain

The 500-MHz¹H-NMR characteristics of theN-linked carbohydrate chain Man1-6[Xyl1-2]Man1-4GlcNAc1-4[Fuc1-3]GlcNAc1-NAsn of the proteolytic enzyme bromelain (EC 3.4.22.4) from pineapple stem were determined for the oligosaccharide-alditol and the glycopeptide, obtained by hydrazinolysis and Pronase digestion, respectively. The¹H-NMR structural-reporter-groups of the (1–3)-linked fucose residue form unique sets of data for the alditol as well as for the glycopeptide.     

Two-dimensional 1H NMR study of two cyclobutane type photodimers of thymidylyl-(3′→5′)-thymidine

2D NMR spectroscopy and J coupling constant analysis are applied to resolve the structure of two photoproducts of thymidylyl-(35)-thymidine. These products are cyclobutane type thymine dimers possessing the cis-syn (the predominant one) and trans-syn geometry. The cis-syn is formed in an ANTI-ANTI conformation about the N-glycosyl linkages and resembles the normal base-stacked configuration. The glycosidic conformation in solution of the 5 terminal fragment differs from the crystal in which the less common SYN conformation is observed. In this isomer only the sugar pucker of the 3 terminal fragment is changed substantially with respect to the dinucleotide. The trans-syn isomer is formed in a SYN-ANTI glycosidic conformation. In this isomer the sugar puckers of both deoxyribose rings are affected and a preference for a pure 2-endo conformation is observed.Abbreviations dTpdT 2-deoxythymidylyl-(35)-2-deoxythymidine - dTp[]dT cyclobutane type photodimers of dTpdT - dTp- and dTp[]- their 5' terminal fragments (fragment A) - -pdT and-[]pdT their 3 terminal fragments (fragment B) - RP-HPLC reversed-phase high-performance liquid chromatography - COSY two-dimensional correlated spectroscopy - 2D NOE two-dimensional nuclear Overhauser spectroscopy     

The Use of the [13C]/[12C] Ratio for the Assay of the Microbial Oxidation of Hydrocarbons

The study deals with a comparative analysis of the relative abundances of the carbon isotopes ¹²C and ¹³C in the metabolites and biomass of the Burkholderia sp. BS3702 and Pseudomonas putida BS202-p strains capable of utilizing aliphatic (n-hexadecane) and aromatic (naphthalene) hydrocarbons as sources of carbon and energy. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of Burkholderia sp. BS3702 on n-hexadecane (¹³C = –44.6 ± 0.2) were characterized by the values of ¹³C_{CO 2} = –50.2 ± 0.4, ¹³C_biom = –46.6 ± 0.4, and ¹³C_exo = –41.5 ± 0.4, respectively. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of the same bacterial strain on naphthalene (¹³C = –21 ± 0.4) were characterized by the isotope effects ¹³C_{CO 2} = –24.1 ± 0.4, ¹³C_biom = –19.2 ± 0.4, and ¹³C_exo = –19.1 ± 0.4, respectively. The possibility of using the isotope composition of metabolic carbon dioxide for the rapid monitoring of the microbial degradation of petroleum hydrocarbons in the environment is discussed.     

Structure of a new nonasaccharide isolated from human milk: VI2Fuc,V4Fuc,III3Fuc-p-lacto-N-hexaose

The structure of a new nonasaccharide isolated from human milk has been investigated. By using methylation analysis, FAB-MS and¹H-and¹³C-NMR spectroscopy as basic methods of structural investigation, this oligosaccharide was identified as VI²--Fuc,V⁴-Fuc,III³--Fuc-p-lacto-n-hexaose: Fuc1-2Gal1-3[Fuc1-4]GlcNAc1-3Gal1-4[Fuc1-3]GlcNAc1-3Gal1-4Glc.Abbreviations COSY correlation spectroscope - DP degree of polymerisation - FAB-MS fast atom bombardment-mass spectrometry - HPLC high performance liquid chromatography - NMR nuclear magnetic resonance - GLC gas-liquid chromatography     

Comparative water-use efficiency of Sporobolus arabicus and Leptochloa fusca and its relation with carbon-isotope discrimination under semi-arid conditions

Water-use efficiency (WUE) of Leptochloa fusca (L.) Kunth (Kallar grass) and Sporobolus arabicus Boiss. was determined under different soil moisture regimes. Plants grown in lysimeters were subjected to three soil moisture regimes, viz. well-watered (100%), medium-watered (75%), and low-watered (50%) of total available water (TAW). The soil moisture was restored on alternate days by adding the required volume of water on the basis of neutron moisture meter readings taken from neutron access tubes installed in each lysimeter. The grasses were harvested after suitable intervals (4 months) to obtain maximum biomass. Leaf samples collected at each harvest were analyzed for carbon-isotope discrimination (¹³C) with an isotope ratio (¹³C/¹²C) mass spectrometer. Results indicated significant differences in WUE of both grasses subjected to different water regimes. Sporobolus arabicus showed higher WUE than Kallar grass. However, Kallar grass showed better value of yield response factor (k _y = 0.649) compared with Sporobolus (k _y = 1.06) over the entire season. The data confirm that these grasses can be grown successfully in water-limited environments by selecting an optimum soil moisture level for maximum biomass production. The mean carbon-isotope discrimination (¹³C) of Kallar grass (–14.4) and Sporobolus (–12.8) confirm that both are C₄ plants. The carbon-isotope discrimination () was significantly and negatively correlated with WUE of the two species studied. The results of the present study confirm that ¹³C or of leaves can be used as good predictor of WUE in some C₄ plants.     

The effect of 17O on the relaxation of an amide proton within a hydrogen bond

Summary The relaxation rates of the multiple-quantum coherence for the amide hydrogen of Gly¹³ in ras p21·GDP were determined in the presence and absence of ¹⁷O labeling in the -phosphate of GDP. No significant difference could be observed between labeled and unlabeled samples, in spite of the fact that the hydrogen bond from the amide group of Gly¹³ to the -phosphate is shorter than is typical, based on its chemical shift. For macromolecules in which an oxygen atom is the acceptor of a hydrogen bond, dipolar coupling between ¹⁷O and hydrogen is unlikely to be observable, except for extremely short H-bonds.Abbreviations p21 21-kD protein product of the human H-ras gene - GMPPCP guanylyl [,-methylene]diphosphate - HPLC high-performance liquid chromatography - CSA chemical shift anisotropy - HMQC heteronuclear multiple-quantum coherence