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     

Force frequency relation in the myocardium of rainbow trout

Summary Isolated heart ventricular preparations from rainbow trout were electrically stimulated to contraction. Following a temporary change in stimulation rate from 0.2 Hz to a higher value, the force fell to a minimum after which it increased and levelled off. Upon the return to 0.2 Hz a further transient increase in force appeared. The latter two responses were stimulated by an increased extracellular K⁺, which is known to inactivate the Na⁺ channel. The initial negative inotropic effect, in contrast to the two subsequent positive effects, was associated with a parallel decrease in amplitude of the action potential measured in 15 mM K⁺, used as an index of the Ca²⁺ influx. One micromolar (1 M) ryanodine did not affect either the negative or the positive responses due to an increase in stimulation rate, but depressed the force developed after prolonged periods of rest. Ten micromolar (10 M) adrenaline strongly inhibited the positive effects of an elevation of frequency. An elevation of extracellular Na⁺ from 141 to 166 mM had a similar effect. In conclusion, the positive effects occurring in 15 mM K⁺ do not seem to depend on the initial Na⁺ current. They may nevertheless depend on changes of the cellular Na⁺ balance as suggested by the effects of adrenaline, K⁺ and Na⁺. The functional role of the sarcoplasmic reticulum is unclear.     

Replacement of potassium ions by ammonium ions in different micro-organisms grown in potassium-limited chemostat culture

The biomass concentration extant in potassiumlimited cultures of either Klebsiella pneumoniae or Bacillus stearothermophilus (when growing at a fixed temperature and dilution rate in a glucose/ammonium salts medium) increased progressively as the medium pH value was raised step-wise from 7.0 to 8.5. Because the macromolecular composition of the organisms did not vary significantly, this increase in biomass could not be attributed to an accumulation of storage-type polymers but appeared to reflect a pH-dependent decrease in the cells' minimum K⁺ requirement. Significantly, this effect of pH was not eviden with cultures in which no ammonium salts were present and in which either glutamate or nitrate was added as the sole nitrogen source; however, it was again manifest when various concentrations of NH₄Cl were added to the glutamate-containing medium. This suggested a functional replacement of K⁺ by NH ₄ ⁺ , a proposition consistent with the close similarity of the ionic radii of the potassium ion (1.33 Å) and the ammonium ion (1.43 Å). At pH 8.0, and with a medium containing both glutamate (30 mM) and NH₄Cl (100 mM), cultures of B. stearothermophilus would grow without added potassium at a maximum rate of 0.7 h^-1. Under these conditions the cells contained maximally 0.1% (w/w) potassium (derived from contaminating amounts of this element in the medium constituents), a value which should be compared with one of 1.4% (w/w) for cells growing in a potassiumlimited medium containing initially 0.5 mM K⁺. Qualitatively similar findings were made with cultures of K. pneumoniae; and whereas one may not conclude that NH ₄ ⁺ can totally replace K⁺ in the growth of these bacteria, it can clearly do so very extensively.     

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.