Photosynthetic properties of leaves of a yellow green mutant of wheat compared to its wild type

We investigated several photosynthetic parameters of a virescent mutant of durum wheat and of its wild-type. Electron transport rate to ferricyanide was the same in the two genotypes when expressed on leaf area basis while O₂ evolution of the leaf tissue in saturating light and CO₂ was slightly higher in the yellow genotype. RuBPCase was also slightly higher. Quantum yield per absorbed light was similar in the two genotypes. P700 and Cyt f were less concentrated in the mutant while PS II was only marginally lower. The light response curve of CO₂ assimilation indicated higher level of photosynthesis of the mutant in high light, which corresponded to a lower non-photochemical quenching compared to the wild-type. It is concluded that the reaction centres, cyt f and chlorophyll are not limiting factors of electron transport in wheat seedlings and that electron transport capacity is in excess with respect to that needed for driving photosynthesis. Since the differences in photosynthesis reflect differences in RuBPCase activity, it is suggested that this enzyme limits photosynthesis in wheat seedlings also at high light intensities.Abbreviations cyt f cytochrome f - chl chlorophyll - PS II photosystem II - Pn_max maximum photosynthesis - RuBCase Ribulose, 1-5,bisphosphate carboxylase     

How rapid are the internal reactions of the ubiquinol:cytochrome c 2 oxidoreductase?

The temperature dependence of the partial reactions leading to turn-over of the UQH₂:cyt c ₂ oxidoreductase of Rhodobacter sphaeroides have been studied. The redox properties of the cytochrome components show a weak temperature dependence over the range 280–330 K, with coefficients of about 1 m V per degree; our results suggest that the other components show similar dependencies, so that no significant change in the gradient of standard free-energy between components occurs over this temperature range. The rates of the reactions of the high potential chain (the Rieske iron sulfur center, cytochromes c ₁ and c ₂, reaction center primary donor) show a weak temperature dependence, indicating an activation energy < 8 kJ per mole for electron transfer in this chain. The oxidation of ubiquinol at the Q_z-site of the complex showed a strong temperature dependence, with an activation energy of about 32 kJ mole^–1. The electron transfer from cytochrome b-566 to cytochrome b-561 was not rate determining at any temperature, and did not contribute to the energy barrier. The activation energy of 32 kJ mole^–1 for quinol oxidation was the same for all states of the quinone pool (fully oxidized, partially reduced, or fully reduced before the flash). We suggest that the activation barrier is in the reaction by which ubiquinol at the catalytic site is oxidized to semiquinone. The most economical scheme for this reaction would have the semiquinone intermediate at the energy level indicated by the activation barrier. We discuss the plausibility of this simple model, and the values for rate constants, stability constant, the redox potentials of the intermediate couples, and the binding constant for the semiquinone, which are pertinent to the mechanism of the ubiquinol oxidizing site.Abbreviations (BChl)₂ P870, primary donor of the photochemical reaction center - b/c ₁ complex ubiquinol: cytochrome c ₂ oxidoreductase - cyt b _H cytochrome b-561 or higher potential cytochrome b - cyt b _L cytochrome b-566, or low potential cytochrome b - cyt c ₁, cyt c ₂, cyt c _t cytochromes c ₁ and c ₂, and total cytochrome c (cyt c ₁ and cyt c ₂) - Fe.S Rieske-type iron sulfur center, Q - QH₂ ubiquinone, ubiquinol - Q_z, Q_zH₂, Q_z ^– ubiquinone, ubiquinol, and semiquinone anion of ubiquinone, bound at quinol oxidizing site - Q_z-site ubiquinol oxidizing site (also called Q_o-(outside) - Q_o (Oxidizing) - Q_P (Positive proton potential) site) - Q_c-site uubiquinone reductase site (also called the Q_i-(inside) - Q_R (Reducing), or - Q_N (Negative proton potential) site) - UHDBT 5-(n-undecyl)-6-hydroxy-4,7-dioxobenzothiazol     

One-carbon compounds transport studies in the obligate methylotroph

Cells of obligate methylotrophic Gram-negative bacterium Methylobacillus flagellatum KT which can only grow on methanol and methylamine media possess three different carriers mediating uptake of methylamin depending on growth conditions. All three uptake systems are energy-dependent, the methylamine uptake was inhibited by oxidative phosphorylation uncoupler and respiratory inhibitors. The first active transport system for methanol in the cells of obligate methylotroph was also demonstrated. The parameters of this system were measured, their dependence on energy, presence of respiratory inhibitors and uncoupler was shown.Abbreviations CCCP Carbonyl cyanide p-(trichloromethoxy)-phenylhydrazone - DCCD N,N-dicyclohexyl-carbodiimide     

Secondary transport of amino acids by membrane vesicles derived from lactic acid bacteria

Lactococci are fastidious bacteria which require an external source of amino acids and many other nutrients. These compounds have to pass the membrane. However, detailed analysis of transport processes in membrane vesicles has been hampered by the lack of a suitable protonmotive force (pmf)-generating system in these model systems. A membrane-fusion procedure has been developed by which pmf-generating systems can be functionally incorporated into the bacterial membrane. This improved model system has been used to analyze the properties of amino acid transport systems in lactococci. Detailed studies have been made of the specificity and kinetics of amino acid transport and also of the interaction of the transport systems with their lipid environment. The properties of a pmf-independent, arginine-catabolism specific transport system in lactococci will be discussed.Abbreviations pmf protonmotive force - transmembrane electrical potential - pH transmembrane pH gradient - PE phosphatidylethanolamine - PC phosphatidylcholine Paper adapted from a treatise Secondary Transport of Amino Acids by Membrane Vesicles Derived from Lactic Acid Bacteria and awarded the Kluyver Prize 1988 by the Netherlands Society of Microbiology.     

Thiolutin inhibits utilization of glucose and other carbon sources in cells of Escherichia coli

Thiolutin was found to inhibit the utilization of glucose and other growth substrates in Escherichia coli. The inhibition was detected by a sharp drop of the respiration rate after addition of the antibiotic. The actual function affected was allocated to the cytoplasmic membrane of the bacterial cells by the following evidence:

Sediment transport in an inland river in North Queensland

Rivers in northern Queensland are ephemeral and carry water mainly as a direct response to heavy rainfall. Sediment is transported downstream with the runoff and sediment deposition may be a major problem in many proposed reservoirs. Hence information about sediment transport, particularly under high flow conditions, is required for planning and design of water storage reservoirs. In this region, bed material samples can be obtained during low flow periods and suspended sediment sampling during floods is possible but only with difficulty. Little reliable data is available.This paper outlines a possible approach to predicting sediment loads in such rivers. Suspended sediment samples have been analysed to give both particulate concentrations and their grain size distributions. The latter have been compared with bed material size distributions, and the concentrations of suspended bed material and wash load components have been estimated.After investigations of a number of methods for predicting bed material transport, those which treat bed load and suspended load independently have been selected. Field data have been used to determine the wash load and the suspended bed material load. The bed load was then computed so that the total sediment load could be determined.This approach has been applied to the Flinders River at Glendower, based on field data obtained by the Queensland Water Resources Commission in 1982/83.     

Fatty acid-binding to erythrocyte ghost membranes and transmembrane movement

Summary Palmitate binding to human erythrocyte ghost membranes has been investigated with ghost preparations suspended in 0.2% albumin solutions. Free unbound palmitate in the extracellular water phase was measured in equilibrium studies using albumin-filled acid loaded ghosts as small semipermeable bags. The apparent dissociation constant of binding to the membrane is 13.5 nM and the binding capacity 19 nmoles per 7.2 × 109 cells.The 0°C exchange efflux kinetics of palmitate from albumin-filled ghosts is described by a model, which provides estimates of the rate constant of membrane transfer, k₃ = 0.024 s^–1, independent of the molar ratio of palmitate to albumin () and of a mean dissociation rate constant of the palmitate-albumin complex, k₁ = 0.0015 s^–1 at 0.2, allowing for a heterogeneity of the palmitate binding to albumin.The values of a third kinetically determined dependent model constant, Q, the ratio of palmitate bound to the membrane inner surface to palmitate on intracellular albumin, are not different from the Q values obtained by equilibrium experiments.The temperature dependences of k₁ and k₃ in the interval 0°C to 15°C give activation energies of 96 and 103 kJ/mole, respectively. The 0°C exchange efflux increases about 2 fold in response to a rise of pH from 6 to 9. The results suggest a carrier mediated palmitate flux at low with a V_max about 2 pmoles min^–1 cm^–2 at 0°C pH 7.3.     

Oxidation of glycerol,lactate, and propionate by Propionibacterium freudenreichii in a poised-potential amperometric culture system

Growth of Propionibacterium freudenreichii was studied with glycerol, lactate, and propionate as energy sources and a three-electrode poised-potential amperometric electrode system with hexacyanoferrate (III) as mediator. In batch culture experiments with glycerol and lactate as substrates, hexacyanoferrate (III) was completely reduced. Growth yields increased and the fermentation patterns were shifted towards higher acetate formation with increasing hexacyanoferrate (III) concentrations (0.25–8.0 mM). In experiments with regulated electrodes, glycerol, lactate, and propionate were oxidized to acetate and CO₂, and the electrons were quantitatively transferred to the working electrode. Growth yields of 29.0, 13.4 and 14.2 g cell material per mol were calculated, respectively. The high cell yield obtained during propionate oxidation cannot be explained solely by substrate level phosphorylation indicating that additional energy was conserved via electron transport phosphorylation. Furthermore, this result indicated complete reversibility of the methyl-malonyl-CoA pathway in propionic acid bacteria.     

How does l-glutamate transport relate to selection of mixed nitrogen sources in Rhizobium leguminosarum biovar trifolii MNF1000 and cowpea Rhizobium MNF2030?

When growing on a mixture of ammonia and l-glutamate as nitrogen sources, Rhizobium leguminosarum biovar trifolii MNF1000 utilizes ammonia exclusively, while cowpea Rhizobium MNF2030 utilizes both compounds at similar rates. l-Glutamate transport in both strain MNF1000 and MNF2030 is active, giving rise to a 60-fold concentration gradient across the membrane of cells of strain MNF2030. Both strains produce two kinetically distinguishable glutamate transport systems under all conditions of growth — a high affinity system with an apparent K _m of 0.06–0.17 M but of relatively low V _max, and a low affinity system with a K _m of 1.2–6.7\ M, but of higher overall capacity. l-Glutamate transport activity in cells of MNF2030 was relatively insensitive to the presence of ammonia in the growth medium. By contrast, ammonia in the growth medium resulted in low activities of glutamate transport in cells of MNF1000 which were provided with a carbon source, offering one explanation for the failure of this strain to use glutamate in the presence of ammonia. However, in cells of MNF1000 growing on glutamate as sole source of carbon and nitrogen, the glutamate transport system is synthesized, even in the presence of accumulated or added ammonia. This suggests that the regulation of the glutamate permease also depends on availability of carbon source.Abbreviations CCCP carbonyl cyanide m-chlorophenyl hydrazone - HEPES N-hydroxyethylpiperazine-N-2-ethanesulphonic acid     

4-aminobutyrate is not available to bacteroids of cowpea Rhizobium MNF2030 in snake bean nodules

Laboratory cultures of cowpea Rhizobium MNF2030 grew on 4-aminobutyrate (GABA) as sole source of carbon and nitrogen. GABA transport was active since it was inhibited by carbonyl cyanide mchlorophenyl hydrazone and 2,4-dinitrophenol and cells developed a 400-fold concentration gradient across the cell membrane. Arsenite treatment of GABA-grown cells revealed stoichiometric conversion of GABA to pyruvate, indicating that 2-oxoglutarate is not an intermediate in GABA catabolism. GABA catabolism by cells of strain MNF2030 grown on GABA appreared to involve GABA transaminase, succinic semialdehyde dehydrogenase and malic enzyme; the first two enzymes were specifically induced by growth on GABA. The deamination process and removal of NH₃ in cells catabolizing GABA involved GABA: 2-oxoglutarate transaminase; glutamate: oxaloacetate aminotransferase; asparate: pyruvate aminotransferase and alanine dehydrogenase.Isolated snakebean bacteroids of strain MNF2030 transported only small amounts of GABA and had uninduced levels of GABA catabolic enzymes, even though the nodules contained significant levels of GABA. The data suggest that GABA is not available to snakebean nodule bacteroids, presumably because of a control imposed by the peribacteroid membrane.Abbreviations CCCP Carbonyl cyanide m-chlorophenyl hydrazone - HEPES N-hydroxyethylpiperazine-N-2-ethanesulphonic acid - DTT dithiothreitol - SSAD succinic semialdehyde dehydrogenase - GABAT 4-aminobutyrate transaminase - GABA 4-aminobutyrate