On the rate-limiting step in W-hydroxylation of lauric acid

Incubation of lauric acid with rat liver microsomes and NADPH yielded a mixture of 11-D-, 11-L-, and 12-hydroxylauric acids. 11-L- and 11-D-hydroxylations of 11-²H₂-lauric acid were accompanied by marked isotope effects, indicating that in these reactions splitting of the CH bond is rate limiting. When 11- and 12-hydroxylations of lauric acid were carried out in D₂O, 12-hydroxylation but not 11-hydroxylation was inhibited, showing that different steps are rate limiting in the two reactions.     

Effects of prescribed burning and drought on the solute chemistry of mixed-conifer forest streams of the Sierra Nevada, California

Solute concentrations in atmospheric depositionand stream water were measured in two mixed-conifercatchments (Tharps and Log creeks) in the SierraNevada of California from 1984 through 1995, a periodincluding a 6-year drought and a prescribed burn inone catchment. The effects of prescribed burning inthe Tharps Creek catchment significantly increasedthe concentrations of most solutes in stream water. In the first year after prescribed burning, the VWM(volume-weighted mean) concentrations of acid anionsin stream water increased proportionally more thanthose of the base cations, and ANC (acid neutralizingcapacity) more than doubled. Sulfate and NO ₃ ^- increased proportionally more in streamwater than any other ions after the fire, but pre- andpost-burn VWM pH were not significantlydifferent. VWM SO ₄ ^2- and NO ₃ ^- concentrations the first year after burning occurredwere about 16- and 2,000-fold above pre-burnbaselines, respectively, while that of Cl^-increased 4-fold. Net retention (precipitationinputs minus streamwater outputs) of H⁺,NO ₃ ^- , NH ₃ ⁺ , SO ₄ ^2- and Cl^- occurred in both catchments, except afterprescribed burning of the Tharps Creek catchment inthe fall of 1990, which caused a net export ofSO ₄ ^2- , Cl^- and K⁺ thefirst year after the burn. Most solutes remained abovepre-disturbance concentrations by the end of the thirdyear after burning, whereas H⁺ and SiO₂remained below. Periodic increases in theconcentrations of Na⁺, Ca²⁺ and SO ₄ ^2- , and decreases in ANC and SiO₂occurred during a 6-year drought monitored in theadjacent undisturbed catchment of Log Creek.     

Interactions of glycolate-, HCO 3 - -, Cl--, and H+-balance of Scenedesmus obliquus

Excretion and absorption of glycolate by young cells of Scenedesmus obliquus (Turp.) Krüger strain D₃ grown synchronously with 2% CO₂ was compared after no pretreatment with air (CO₂-adapted) or after a 2 h adaptation to normal air (0.03% CO₂) (air-adapted). At 21% O₂, excretion occurred only from CO₂-adapted cells at high pH (pH 8.0). Under conditions where no excretion occurred, external glycolate (0.2 mM) was taken up by both air-and CO₂-adapted cells at a much faster rate at pH 5 than at pH 8. The uptake was accompanied by an apparent stoichiometric uptake of H⁺. CO₂-adapted algae exhibited high uptake rates that were even higher in the dark than in the light. Air-adapted algae showed high uptake rates in the light but only minimal uptake in the dark. The uptake rate was decreased to about 1/3 with 5% CO₂, except with CO₂-adapted cells in the light, in which a slight stimulation occurred. Cl^- ions inhibited glycolate uptake by air-adapted cells in the light; conversely, light-stimulated Cl^- uptake of these cells was inhibited by glycolate. A hypothesis is discussed according to which the internal pH regulates the uptake and release of Cl^-, HCO ₃ ^- , and glycolate.Abbreviations DCMU 3-(3,4 dichlorophenyl)-1, 1-dimethyl urea - FCCP carbonyl cyanide p-trifluoro-methoxyphenylhydrazone - HEPES 2-(4-(2-hydroxyethyl)-piperazinyl) ethanesulfonic acid - HPMS -hydroxypyridinemethanesulfonate - MES 2-morpholinoethanesulfonic acid - PCV packed cell volume     

Glyoxylate decarboxylation during photorespiration

At 25° C under aerobic conditions with or without gluamate 10% of the [1-¹⁴C]glycollate oxidised in spinach leaf peroxisomes was released as ¹⁴CO₂. Without glutamate only 5% of the glycollate was converted to glycine, but with it over 80% of the glycollate was metabolised to glycine. CO₂ release was probably not due to glycine breakdown in these preparations since glycine decarboxylase activity was not detected. Addition of either unlabelled glycine or isonicotinyl hydrazide (INH) did not reduce ¹⁴CO₂ release from either [1-¹⁴C]glycollate or [1-¹⁴C]glyoxylate. Furthermore, the amount of available H₂O₂ (Grodzinski and Butt, 1976) was sufficient to account for all of the CO₂ release by breakdown of glyoxylate. Peroxisomal glycollate metabolism was unaffected by light and isolated leaf chloroplasts alone did not metabolise glycollate. However, in a mixture of peroxisomes and illuminated chloroplasts the rate of glycollate decarboxylation increased three fold while glycine synthesis was reduced by 40%. Although it was not possible to measure available H₂O₂ directly, the data are best explained by glyoxylate decarboxylation. Catalase reduced CO₂ release and enhanced glycine synthesis. In addition, when a model system in which an active preparation of purified glucose oxidase generating H₂O₂ at a known rate was used to replace the chloroplasts, similar rates of ¹⁴CO₂ release and [¹⁴C]glycine synthesis from [1-¹⁴C]glycollate were measured. It is argued that in vivo glyoxylate metabolism in leaf peroxisomes is a key branch point of the glycollate pathway and that a portion of the photorespired CO₂ arises during glyoxylate decarboxylation under the action of H₂O₂. The possibility that peroxisomal catalase exerts a peroxidative function during this process is discussed.Abbreviations HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulphonic acid - INH isonicotinylhydrazide - PHMS pyridyl-2-yl--hydroxymethane sulphonic acid     

Formation of inorganic protonic-acid polymer via inorganic-organic hybridization: Synthesis and characterization of polymerizable olefinic organosilyl derivatives of mono-lacunary Dawson polyoxometalate

A novel polymerizable organosilyl-modified Dawson-type polyoxometalate (POM) [α₂-P₂W₁₇O₆₁{CH₂C(CH₃)COO(CH₂)₃Si}₂O]⁶⁻ (1) was synthesized as both salt (Me₂NH₂-1) and H⁺ form (H-1). They were characterized with complete elemental analysis, thermogravimetric and differential thermal analysis (TG/DTA), FTIR, (¹H, ¹³C, ²⁹Si, ³¹P and ¹⁸³W) NMR and n-butylamine titration method. H-1 was immobilized to a polymer network through free radical copolymerization with methyl methacrylate (MMA). The acidities of H-1 and hybrid copolymer (H-1-co-MMA) were evaluated using the Hammett indicators (dicinnamalacetone and benzalacetophenone; pK_a values of the protonated indicators are −3.0 and −5.6, respectively). The pK_a value of H-1 was estimated as that between −3.0 and −5.6 in CH₃CN solution and H-1 was immobilized in H-1-co-MMA with the original acidity being retained. Glass transition point (T_g) and molecular weight distribution of H-1-co-MMA were affected by the used amount of H-1 because of the cross-linking effect of H-1.     

The formation,vacuolar localization,and tonoplast transport of salicylic acid glucose conjugates in tobacco cell suspension cultures

The metabolism of salicylic acid (SA) in tobacco (Nicotiana tabacum L. cv. KY 14) cell suspension cultures was examined by adding [7–¹⁴C]SA to the cell cultures for 24 h and identifying the metabolites through high performance liquid chromatography analysis. The three major metabolites of SA were SA 2-O--D-glucose (SAG), methylsalicylate 2-O--D-glucose (MeSAG) and methylsalicylate. Studies on the intracellular localization of the metabolites revealed that all of the SAG associated with tobacco protoplasts was localized in the vacuole. However, the majority of the MeSAG was located outside the vacuole. The tobacco cells contained an SA inducible SA glucosyltransferase (SAGT) enzyme that formed SAG. The SAGT enzyme was not associated with the vacuole and appeared to be a cytoplasmic enzyme. The vacuolar transport of SAG was characterized by measuring the uptake of [¹⁴C]SAG into tonoplast vesicles isolated from tobacco cell cultures. SAG uptake was stimulated eightfold by the addition of MgATP. The ATP-dependent uptake of SAG was inhibited by bafilomycin A₁ (a specific inhibitor of the vacuolar H⁺-ATPase) and dissipation of the transtonoplast H⁺-electrochemical gradient. Vanadate was not an inhibitor of SAG uptake. Several -glucose conjugates were strong inhibitors of SAG uptake, whereas glutathione and glucuronide conjugates were only marginally inhibitory. The SAG uptake exhibited Michaelis–Menten type saturation kinetics with a K_m and V_max value of 11 M and 205 pmol min^–1 mg^–1, respectively, for SAG. Based on the transport characteristics it appears as if the vacuolar uptake of SAG in tobacco cells occurs through an H⁺-antiport-type mechanism.     

An NMR study of some reactions of an arachno-molybdapentaborane: Formation of an unstable nido-molybdapentaborane

Photolysis of the molybdaborane [(η⁵-C₅H₅)(η⁵:η¹-C₅H₄)-arachno-2-MoB₄H₇] (1) in benzene-d₆ gives ca. 60% conversion to the compound [(η⁵-C₅H₅)(η⁵:η¹-C₅H₄)-nido-2-MoB₄H₅] (2). Compound 2 could not be isolated as a solid and is thermally unstable at 20 °C in solution with a half-life of 3-4 h. Repeated photolysis and thermolysis of 1 in the presence of BH₃ · thf gives a low yield of the known metallacarbaborane [(η⁵-C₅H₅)(η²:η³-C₃H₃)-closo-1-MoC₂B₉H₉] (3) suggesting that 3 is formed from 1 via 2. Reaction of 1 with PEt₃ gives initially [(η⁵-C₅H₅)(η⁵:η¹-C₅H₄)-arachno-2-MoHB₄H₄PEt₃] (4). Longer reaction times (>10 min, 20 °C) give in addition [(η⁵-C₅H₅)(η⁵:η¹-C₅H₄)-arachno-1-MoHB₃H₃PEt₃] (5). Both 4 and 5 are unstable in solution or the solid state decomposing to the molybdacarbaborane [(η⁵-C₅H₅)(η³:η²- C₃H₃)-nido-1-MoC₂B₃H₅] (6), [Mo(η-C₅H₅)₂H₂] and BH₃ · PEt₃. Compound 1 is deprotonated cleanly by KH in thf at the Mo-H-B bridging proton to give (7).     

Metabolism of gibberellin A29 in seeds of Pisum sativum cv. Progress No. 9; Use of [2H] and [3H]GAs,and the identification of a new GA catabolite

The metabolism of GA₂₉ in maturing seeds of Pisum sativum cv. Progress No. 9 was further investigated, and the utility of ²H-labelled GAs in conjuction with GC-MS is illustrated. Using [2-²H₁]GA₂₉ as an internal standard, endogenous GA₂₉ was shown to reach a maximal level (ca. 10 g/seed) 27 days from anthesis, and to decline to ca. 1.6 g/seed in mature seeds. In a time-course feed the metabolism of [2-²H₁] [2-³H₁]GA₂₉ applied to 27 day old seeds, and of endogenous GA₂₉, was compared from the ¹H:²H ratios in the recovered GA₂₉. Although both [2-²H₁] [2-³H₁]GA₂₉ and endogenous GA₂₉ were metabolised to the same limited extent to a putative conjugate, in the main metabolic process endogenous GA₂₉ was preferentially converted to an untraceable (i.e. unlabelled) metabolite. In contrast, endogenous GA₂₉ and [1,3-²H₂] [1,3-³H₂]GA₂₉, derived from [1,3-²H₂] [1,3-³H₂]GA₂₀ in a time-course feed, were metabolised in an identical manner. In the latter case isotope loss precluded identification of the metabolite. The structure (8) has been assigned to a GA catabolite present in maturing seeds and seedlings of pea. The isotope data are consistent with this compound being the hitherto untraced metabolite of GA₂₉ in pea.Abbreviations GA_n gibberellin A_n - GC gas chromatography - GC-MS combined gas chromatography-mass spectrometry - GC-RC combined gas chromatography-radio counting - M⁺ molecular ion - Me methyl ester - R_T retention time - SICM selected ion current monitoring - TLC thin layer chromatography - TMS trimethylsilyl ether     

The role of the Krebs cycle in the generation of intramitochondrial reducing equivalents for the 11 beta-hydroxylation of deoxycorticosterone in isolated rat adrenal cells

Isolated rat adrenal cells were used to study the possible pathways of intramitochondrial NADPH generation for 11β-hydroxylation of 11-deoxycorticosterone. Pyruvate was efficiently utilized by the mitochondria as shown by evolution of ¹⁴CO₂ from [1-¹⁴C]- and [2-¹⁴C]pyruvate. Citrate, isocitrate, succinate, and malate were not utilized by intact cells due to their inability to permeate the plasma membrane. For every mole of corticosterone formed, 1.9 and 0.8 moles of ¹⁴CO₂ were formed from [1-¹⁴C]- and [2-¹⁴C]pyruvate, respectively, indicating that pyruvate dehydrogenase was quite active and supplied acetyl C?oA to the Krebs cycle. Fluorocitrate and 2,4-dinitrophenol inhibited 11β-hydroxylation of 11-deoxycorticosterone as well as the production of ¹⁴CO₂ from [2-¹⁴C]pyruvate. Comparison of data with the two inhibitors showed that for the same percentage of inhibition of ¹⁴CO₂ production, the inhibition of 11β-hydroxylation was greater with 2,4-dinitrophenol than with fluorocitrate. It is concluded that operation of the Krebs cycle may be essential for 11β-hydroxylation to occur primarily because NADH generated by the cycle provides ATP, via the respiratory chain, as well as the substrate for the energy-linked transhydrogenase that forms NADPH. The NADPH required for 11β-hydroxylation seems to be derived to a large extent via the energy-linked transhydrogenase.     

Facile Preparation of Deuterium-Labeled Standards of Indole-3-Acetic Acid (IAA) and Its Metabolites to Quantitatively Analyze the Disposition of Exogenous IAA in Arabidopsis thaliana

[2′,2′-²H₂]-indole-3-acetic acid ([2′,2′-²H₂]IAA) was prepared in an easy and efficient manner involving base-catalyzed hydrogen/deuterium exchange. 1-O-([2′,2′-²H₂]-indole-3-acetyl)-β-D-glucopyranose, [2′,2′-²H₂]-2-oxoindole-3-acetic acid, and 1-O-([2′,2′-²H₂]-2-oxoindole-3-acetyl)-β-D-glucopyranose were also successfully synthesized from deuterated IAA, and effectively utilized as internal standards in the quantitative analysis of IAA and its metabolites in Arabidopsis thaliana by using liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS). The use of this technique shows that these metabolites were accumulated in the roots of Arabidopsis seedlings. Dynamic changes in the metabolites of IAA were observed in response to exogenous IAA, revealing that each metabolic action was regulated differently to contribute to the IAA homeostasis in Arabidopsis.     

Au(III)-complexes of the alanyl-containing peptides glycylalanine and glycylalanylalanine - Synthesis, spectroscopic and structural characterization

As part of an investigation on the coordination ability of peptides, the dipeptide glycylalanine (H-Gly-Ala-OH), tripeptide glycylalanylalanine (H-Gly-Ala-Ala-OH) and their Au(III)-complexes have been characterized structurally. The quantum chemical calculations and linear-dichroic infrared (IR-LD) spectroscopy predict structures of the compound studied, which are compared with a single crystal X-ray diffraction of H-Gly-Ala-OH. The coordination processes with Au(III) are supported by data for ¹H NMR, ESI-MS, HPLC-MS-MS, TGV and DSC methods. The [Au(Gly-Ala)H₋₁Cl] and [Au(Gly-Ala-Ala)H₋₂] · 2H₂O complexes are formed via -NH₂, N⁻amide/s and groups of the peptides. One Cl⁻ ion is attached to the metal center as terminal ligand in the first complex. In both cases a near to square-planar geometry of the chromophors AuN₂OCl and AuN₃O is yielded.     

Biospeciation, by potentiometry and computer simulation, of Sm-EDTMP, a bone tumor palliative agent

¹⁵³Sm-EDTMP (ethylenediaminetetra(methylenephosphonic) acid) is of considerable interest as a bone therapeutic radiopharmaceutical but its properties in solution are not yet well characterized. The protonation constants of EDTMP and the formation constants of the complexes of Sm-EDTMP have accordingly been measured potentiometrically by glass electrode titrations at 25°C in 0.15 M NaCl. Six protonation constants (log ₀₁₁ = 9.638, log ₀₁₂ = 17.330, log ₀₁₃ = 23.597, log ₀₁₄ = 28.636, log ₀₁₅ = 31.501, log ₀₁₆ = 32.624) and the formation constants of the [Sm(EDTMP)H_-1]^6- (log _11-1 = 4.865), [SmEDTMP]^5- (log ₁₁₀ = 12.018), [Sm(EDTMP)H]^4- (log ₁₁₁ = 17.892) and [Sm(EDTMP)H₂]^3- (log ₁₁₂ = 23.437) complexes were determined. Computer simulations indicate that the [SmEDTMP]^5- and the hydroxy [Sm(EDTMP)H_-1]^6- species are the major Sm(III) complexes formed in blood plasma, which explains the high degree of localization in the kidney and urine observed in biodistribution studies. Calcium ions are probably the maior competitor for EDTMP in blood plasma. As the presence of secondary skeletal metastases results in a high rate of bone turnover, it is possible that the high concentration of calcium at these sites encourages localization of ¹⁵³Sm-EDTMP.     

Inhibition of the catalase reaction of Photosystem II by anions

A new binding site for anions which inhibit the water oxidizing complex (WOC) of Photosystem II in spinach has been identified. Anions which bind to this site inhibit the flash-induced S₂/S₀ catalase reaction (2H₂O₂2H₂O+O₂) of the WOC by displacing hydrogen peroxide. Using a mass spectrometer and gas permeable membrane to detect the ³²O₂ product, the yield and lifetime of the active state of the flash-induced catalase (to be referred to simply as flash-catalase) reaction were measured after forming the S₂ or S₀-states by a short flash. The increase in flash-catalase activity with H₂O₂ concentration exhibits a K_m=10–20 mM, and originates from an increase in the lifetime by 20-fold of the active state. The increased lifetime in the presence of peroxide is ascribed to formation of the long-lived S₀-state at the expense of the unstable S₂-state. The anion inhibition site differs from the chloride site involved in stimulating the photolytic water oxidation reaction (2H₂OO₂+4e^-+4H⁺). Whereas water oxidation requires Cl^- and is inhibited with increasing effectiveness by F^-CN^-N₃ ^-, the flash-catalase reaction is weakly inhibited by Cl^-, and with increasing effectiveness by F^-CN^-, N₃ ^-. Unlike water oxidation, chloride is unable to suppress or reverse inhibition of the flash-catalase reaction caused by these anions. The inhibitor effectiveness correlates with the pK_a of the conjugate acid, suggesting that the protonated species may be the active inhibitor. The reduced activity arises from a shortening of the lifetime of the flash-induced catalase active state by 3–10 fold owing to stronger anion binding in the flash-induced states, S₂ and S₀, than in the dark S-states, S₁ and S_-1. To account for the paradoxical result that higher anion concentrations are required to inhibit at lower H₂O₂ concentrations, where S₂ forms initially after the flash, than at higher H₂O₂ concentrations, where S₀ forms initially after the flash, stronger anion binding to the S₀-state than to the S₂-state is proposed. A kinetic model is given which accounts for these equilibria with anions and H₂O₂. The rate constant for the formation/release of O₂ by reduction of S₂ in the WOC is <0.4 s^-1.Abbreviations ADRY acceleration of the deactivation reactions of the water splitting enzyme system Y - BTP bis [tris(hydroxymethyl)methylamino]-propane - CCCP carbonylcyanide m-chlorophenylhyrazone - DCBQ 2,5-dichlorobenzoquinone - DMBQ 2,3-dimethylbenzoquinone - WOC water oxidizing complex     

Purification and properties of a F420-nonreactive,membrane-bound hydrogenase from Methanosarcina strain Gö1

The distribution of the F₄₂₀-reactive and F₄₂₀-nonreactive hydrogenases from the methylotrophic Methanosarcina strain Gö1 indicated a membrane association of the F₄₂₀-nonreactive enzyme. The membrane-bound F₄₂₀-nonreactive hydrogenase was purified 42-fold to electrophoretic homogeneity with a yield of 26.7%. The enzyme had a specific activity of 359 mol H₂ oxidized · min^-1 · mg protein^-1. The purification procedure involved dispersion of the membrane fraction with the detergent Chaps followed by anion exchange, hydrophobic and hydroxylapatite chromatography. The aerobically prepared enzyme had to be reactivated anaerobically. Maximal activity was observed at 80°C. The molecular mass as determined by native gel electrophoresis and gel filtration was 77000 and 79000, respectively. SDS gel electrophoresis revealed two polypeptides with molecular masses of 60000 and 40000 indicating a 1:1 stoichiometry. The purified enzyme contained 13.3 mol S^2-, 15.1 mol Fe and 0.8 mol Ni/mol enzyme. Flavins were not detected. The amino acid sequence of the N-termini of the subunits showed a higher degree of homology to cubacterial uptake-hydrogenases than to F₄₂₀-dependent hydrogenases from other methanogenic bacteria. The physiological function of the F₄₂₀-nonreactive hydrogenase from Methanosarcina strain Gö1 is discussed.Abbreviations transmembrane electrochemical gradient of H^- - CoM-SH 2-mercaptoethanesulfonate - F₄₂₀ (N-l-lactyl--l-glutamyl)-l-glutamic acid phospodiester of 7,8-didemethyl-8-hydroxy-5-deazariboflavin-5-phosphate - F₄₂₀H₂ reduced F₄₂₀ - HTP-SH 7-mercaptoheptanoylthreonine phosphate - Mb. Methanobacterium - PMSF phenylmethyl-sulfonylfluoride - Cl₃AcOH trichloroacetic acid     

Novel rhodium complexes containing a bulky iminophosphine ligand and their use as catalysts for the hydroboration of vinylarenes

Addition of o-Ph₂PC₆H₄CHN-2,6-ⁱPr₂C₆H₃ (1) to [RhCl(coe)₂]₂ (coe = cis-cycloctene) gave several new iminophosphino rhodium(I) complexes including [Rh(κ²-o-Ph₂PC₆H₄CHN-2,6-ⁱPr₂C₆H₃)(μ-Cl)]₂ (2). Addition of 1 to Rh(acac)(coe)₂ (acac = acetylacetonato) gave [Rh(acac)(κ²-o-Ph₂PC₆H₄CHN-2,6-ⁱPr₂C₆H₃)] (3) in yields of up to 75%. Complex 3 has been examined for its ability to catalyze the hydroboration of a series of vinyl arenes. Reactions using catecholborane and pinacolborane seem to proceed largely through a dehydrogenative borylation mechanism to give a number of boronated products.     

Influence of anions on the potassium status and productivity of kiwifruit (Actinidia deliciosa) vines

The effects of K fertiliser (160 kg ha^-1) applied with Cl^- or SO₄ ^2- as the accompanying anion on the K nutrition of kiwifruit (Actinidia deliciosa var. deliciosa) were assessed in a field experiment, using vines with varying degrees of K deficiency. Leaf K concentrations in spring were significantly higher for vines receiving KCl, compared to those receiving K₂SO₄. This effect did not interact significantly with the degree of K deficiency, and persisted for about 6 weeks. Subsequently there was no significant difference between the leaf K concentrations for the vines receiving KCl or K₂SO₄. Applying K as KCl increased the leaf Cl concentration, especially in spring, while applying K as K₂SO₄ had no significant effect on the leaf S concentration at that time. These results implied a greater requirement for organic acid anions for K⁺ uptake from K₂SO₄ than from KCl, and the importance of organic acid anions for K⁺ uptake from different sources of K fertiliser is discussed. This transient effect of the accompanying anion on leaf K status was associated with large effects on flowering, and fruit yields were about 28% higher for plants receiving KCl rather than K₂SO₄.The effects on growth and tissue nutrient composition of varying the concentrations of Cl^-, NO₃ ^-, SO₄ ^2- and H₂PO₄ ^- around the roots of kiwifruit vines were examined in a solution culture experiment. For H₂PO₄ ^-, plant growth was very similar over a wide range of rates of addition. For the other anions, the range between deficiency and toxicity was clearly delineated. For Cl^- and NO₃ ^-, toxicity was associated with high tissue concentrations of Cl and N, respectively, and was consistent with competition for uptake between Cl^- and NO₃ ^-. However, for SO₄ ^2-, toxicity was associated with only a small increase in the tissue S concentration relative to that associated with maximum growth, and appeared to result more from effects on uptake of other anions and cations rather than from direct effects of high tissue S concentrations.It is concluded that the sensitivity of kiwifruit to the anion accompanying K⁺ in fertiliser may be related to the unusually high requirement for Cl previously reported for this species.     

Synthesis, structure, and characterization of some ruthenium arene complexes of N-(arylmethylene)-2-(methylthio)anilines and 2-(methylthio)aniline

A series of cationic, half-sandwich ruthenium complexes with the general formula [(η⁶-p-cymene)RuCl(MeSC₆H₄2-NCHAr)][PF₆] (3a-h), have been prepared from the reaction of [(η⁶-p-cymene)RuCl₂]₂ with various N,S-donor Schiff base ligands derived from 2-(methylthio)aniline and several substituted benzaldehydes. The related aniline complex [(η⁶-p-cymene)RuCl(MeS-C₆H₄-2-NH₂)][PF₆] (4) was synthesized from 2-(methylthio)aniline. All of the ruthenium complexes were characterized by IR, ¹H NMR, and UV/Vis spectroscopies. The molecular structure of complex 4 was determined by X-ray crystallography.     

The effect of temperature on glycollate decarboxylation in leaf peroxisomes

[1-¹⁴C]glycollate was oxidised to¹⁴CO₂ by peroxisomes isolated from leaves of spinach beet about 3 times as rapidly at 35°C as at 25°C; the rate was further increased with rise in temperature to a maximum at 55°C. These increases are shown to be mainly due to the increased H₂O₂ available to oxidise glyoxylate non-enzymically as a result of the higher temperature coefficient of glycollate oxidase activity relative to that of catalase. These results are compared with similar increases in the rate of¹⁴CO₂ release between 25°C and 35°C when [1-¹⁴C]glycollate was supplied to leaf discs in light or darkness. The role of these reactions in accounting for the temperature effect on the release of photorespiratory CO₂ is discussed.Abbreviations PHMS Pyrid-2-yl--hydroxymethane sulphonate - FMN flavin mononucleotide     

Proton conductance caused by long-chain fatty acids in phospholipid bilayer membranes

Summary Mechanisms of proton conductance (G _H) were investigated in phospholipid bilayer membranes containing long-chain fatty acids (lauric, myristic, palmitic, oleic or phytanic). Membranes were formed from diphytanoyl phosphatidylcholine in decane plus chlorodecane (usually 30% vol/vol). Fatty acids were added either to the aqueous phase or to the membrane-forming solution. Proton conductance was calculated from the steadystate total conductance and the H⁺ diffusion potential produced by a transmembrane pH gradient. Fatty acids causedG _H to increase in proportion to the first power of the fatty acid concentration. TheG _H induced by fatty acids was inhibited by phloretin, low pH and serum albumin.G _H was increased by chlorodecane, and the voltage dependence ofG _H was superlinear. The results suggest that fatty acids act as simple (A^– type) proton carriers. The membrane: water partition coefficient (K _p ) and adsorption coefficient () were estimated by finding the membrane and aqueous fatty acid concentrations which gave identical values ofG _H. For palmitic and oleic acidsK _p was about 10⁵ and was about 10^–2 cm. The A^– translocation or flip-flop rate (k _a ) was estimated from the value ofG _H and the fatty acid concentration in the membrane, assuming that A^– translocation was the rate limiting step in H⁺ transport. Thek _A 's were about 10^–4 sec^–1, slower than classical weak-acid uncouplers by a factor of 10⁵. Although long-chain fatty acids are relatively inefficient H⁺ carriers, they may cause significant biological H⁺ conductance when present in the membrane at high concentrations, e.g., in ischemia, hypoxia, hormonally induced lipolysis, or certain hereditary disorders, e.g., Refsum's (phytanic acid storage) disease.     

Syn-anti and anti-anti conformations of a diimine derived from p-xylylenediamine and its neutral Co and Zn dinuclear complexes

A symmetric diimine ligand containing a CH₂PhCH₂ bridging group (H₂XyTs: N,N′-bis(2-tosylaminobenzylidene)-1,4-xylylenediamine) and its neutral Co^II and Zn^II dinuclear complexes have been prepared. Two different crystal structures of the free ligand, H₂XyTs, and that corresponding to [Co₂(XyTs)₂], have been solved by X-ray diffraction methods. These revealed two different conformations (syn-anti and anti-anti) for H₂XyTs and an infrequent rotational isomerism on the xylylene rings of its Co^II dinuclear complex, where both ligands are syn-anti conformed. Characterisation of the compounds is completed with FT-IR, ESI-MS and ¹H NMR spectroscopic techniques, when possible.