Internal P loading in lakes: A different approach to its evaluation

P release rates in five lakes were estimated from a mass balance approach and from laboratory tests. The influence of various environmental parameters on P release has been considered. The internal P loading can contribute phosphorus to overlying waters at levels comparable to the external sources (from 30 to 100%). When considering the recovery from eutrophication of the investigated lakes, the nutrient release from sediments is of critical importance.     

The electrochemical H+ gradient in the yeastRhodotorula glutinis

The electrochemical gradient of protons, , was estimated in the obligatory aerobic yeastRhodotorula glutinis in the pH₀ range from 3 to 8.5. The membrane potential, , was measured by steady-state distribution of the hydrophobic ions, tetraphenylphosphonium (TPP⁺) for negative above pH₀ 4.5, and thiocyanate (SCN^–) for positive below pH₀ 4.5. The chemical gradient of H⁺ was determined by measuring the chemical shift of intracellular P_i by³¹P-NMR at given pH₀ values. The values of pH_i increased almost linearly from 7.3 at pH₀ 3 to 7.8 at pH₀ 8.5. In the physiological pH₀ range from 3.5 to 6, was fairly constant at values between 17–18 KJ mol^–1, gradually decreasing at pH₀ above 6. In deenergized cells, the intracellular pH_i decreased to values as low as 6, regardless of whether the cell suspension was buffered at pH₀ 4.5 or 7.5. There was no membrane potential detectable in deenergized cells.     

1H NMR study of the interaction of bacteriophage λ Cro protein with the O R 3 operator

The 17 base pair operator O _R ³ oligonucleotide, which is the preferential binding site for the Cro repressor of phage , was studied by two-dimensional NMR spectroscopy. A sequential assignment procedure based on two-dimensional Nuclear Overhauser Effect (NOESY) and scalar coupling correlated (COSY) NMR spectroscopy, together with the knowledge of the oligodesoxynucleotide sequence, made it possible to assign the non-exhangeable base protons and the H1 and the H2-H2 sugar protons of the O _R ³ operator DNA. The pattern of the observed NOE connectivities is consistent with a right-handed helical DNA structure. The base and sugar proton assignments provide the necessary information for further studies of the O _R ³ operator — Cro repressor interaction.Abbreviations COSY correlated spectroscopy - FID free induction decay - NOE nuclear Overhauser effect - NOESY nuclear Overhauser effect spectroscopy - RD relaxation delay - TSP sodium 3-trimethylsilyl-(2,2,3,3-²H₄)propionate - EDTA sodium ethylendiamine tetraacetate     

A comparison of the translational diffusion of a normal and a membrane-spanning lipid in Lα phase 1-palmitoyl-2-oleoylphosphatidylcholine bilayers

We have used the fluorescence recovery after photobleaching technique to study the translational diffusion, in L phase multibilayers of 1-palmitoyl-2-oleoylphosphatidylcholine (POPC), of fluorescent derivatives of 1-palmitoyl-2-oleoylphosphatidylethanolamine (NBD-POPE) and a membrane-spanning phosphatidylethanolamine (NBD-MSPE). The latter derivative was prepared from a membrane-spanning glycerol-dialkyl-glycerol tetraether lipid isolated from the thermophilic and acidophilic archaebacterium Sulfolobus solfataricus. The translational diffusion was examined between about 15° and 45°C. It is shown that over this temperature range the translational diffusion coefficient for NBD-MSPE is 2/3 that for NBD-POPE which spans only one monolayer of the bilayer. The result is interpreted in terms of existing models for translational diffusion in lipid membranes.Abbreviations D _t translational diffusion coefficient - FRAP fluorescence recovery after photobleaching - MSPE a membrane-spanning phosphatidylethanolamine derived from a glycerol-dialkyl-glycerol tetraether lipid isolated from Sulfolobus solfataricus - NBD 4-nitrobenz-2-oxa-1,3-diazolyl - PE phosphatidylethanolamine - POPC 1-palmitoyl-2-oleoylphosphatidylcholine - POPE 1-palmitoyl-2-oleoylphosphatidylethanolamine     

Influence of structural and physical properties of the thylakoid membrane on QA - oxidation

Using isolated pea thylakoids, the relative rate of Q_A ^- oxidation has been estimated under various conditions, from the restoration of the induction curves following a dark period and from light 1-induced changes in modulated chlorophyll fluorescence excited by light 2.Alterations of _QinfA ^sup– oxidation rates were observed under conditions which affected the degree of thylakoid stacking, the lipid fluidity and the integrity of the membranes. The results are discussed in terms of the interactions between Q_A ^- and the plastoquinone pool with particular emphasis on lateral diffusion.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - EDTA Ethylenediaminetetracetate - Hepes N-2-hydroxyethyl piperazine-N-2-ethanesulphonic acid - NADP nicotinamide adenine dinucleotide phosphate     

The magnesium protein interaction in nucleotide complexes of phos-phoglycerate kinase

The X-ray structure determination of yeast phosphoglycerate kinase and subsequent substrate binding studies have helped to define the binding sites for the triose and nucleoside phosphate substrates. This communication deals with one feature of the binding site—the location of an aspartic acid residue close to the phosphoryl binding site of the nucleotide substrate—and relates this and other structural features of the active site to the properties of this enzyme as deduced from nuclear magnetic resonance studies.     

Diffusion of inorganic carbon across an unstirred layer: a simplified quantitative approach

Abstract The quantitative approach used here is based on a model comprising a well-stirred medium, an unstirred layer, and a CO₂ absorbing leaf. The unstirred layer is divided up by planes into a number of sub-layers. Within each plane the concentration of each solute is everywhere the same as is the electric potential. These variables constitute the basic data. Thus the planes were characterized by their pH value. An equation is derived which enables the calculation of the basic data of a plane from the known data of another plane. In this way it is possible to calculate the basic data for all planes. From these data the rate of assimilation, the thickness of the unstirred layer and its sub-layers, the fluxes across the sub-layers and the conversions among the carbon components can be estimated. The CO₂ flux decreases, and the HCO^?₃ flux increases towards the leaf. There are negative fluxes of OH^& and CO^2–₃. H⁺ fluxes are of minor importance and can be ignored if the pH of the medium is higher than 8.0, provided no non-inorganic C buffers with appropriate pK_a are present. The significance of the carbon diffusion facilitating effect of an inorganic carbon system is expressed in various ways. The values obtained represent maxima, as the assumption is made that the equilibrium reactions are very fast. It is argued that even better effects are possible if the back-diffusion of CO^2–₃ could be prevented by lowering the pH of the unstirred layer.     

CO2 uptake and transport in leaf mesophyll cells

Abstract The acquisition of inorganic carbon for photosynthetic assimilation by leaf mesophyll cells and chloroplasts is discussed with particular reference to membrane permeation of CO₂ and HCO^?₃. Experimental evidence indicates that at the apoplast pH normally experienced by leaf mesophyll cells (pH 6–7) CO₂ is the principal species of inorganic carbon taken up. Uptake of HCO^?₃ may also occur under certain circumstances (i.e. pH 8.5), but its contribution to the net flux of inorganic carbon is small and HCO^?₃ uptake does not function as a CO₂-concentrating mechanism. Similarly, CO₂ rather than HCO^?₃ appears to be the species of inorganic carbon which permeates the chloroplast envelope. In contrast to many C₃ aquatic plants and C₄ plants, C₃ terrestrial plants lack specialized mechanisms for the acquisition and transport of inorganic carbon from the intercellular environment to the site of photosynthetic carboxylation, but rely upon the diffusive uptake of CO₂.     

Optically detected magnetic resonance in lysozyme: evidence for three phosphorescent TRP residues

The Optically Detected Magnetic Resonance spectrum of lysozyme has been shown to consist of a multiplet of narrow components, at -1565 MHz, 1585 MHz, and 1620 MHz. The 1585 MHz component is the strongest feature of the spectrum. This is consistent with earlier reports which apparently resolved only this principal component in lysozyme. The linewidths reported here are the narrowest ever reported for tryptophan in proteins. Using Microwave-Induced Phosphorescence techniques, the dominant 1585 MHz line is seen to be coupled to a "narrow" phosphorescence emission component at about 4134A. This component has a bandwidth of about 25A compared to 42A for the normal O-O band for tryptophan in lysozyme.     

In vitro metabolism of N-methyl-dibenzo [c,g]carbazole a potent sarcomatogen devoid of hepatotoxic and hepatocarcinogenic properties

The metabolism of N-methyl substituted 7H-dibenzo[c,g]carbazole (N-Me DBC) was investigated in vitro using liver microsomes from 3-methylcholanthrene (MC)-, benzo[c]carbazole (BC) and Arochlor-pretreated mice and rats. N-Me DBC is a potent sarcomatogen devoid of hepatotoxicity and liver carcinogenic activity. The ethyl acetate-extractable metabolites were separated by high performance liquid chromatography (HPLC) and most of them were identified by proton magnetic resonance (PMR), mass spectrometry (MS) and comparison with synthetically prepared specimens. Mouse and rat microsomes gave rise to the same metabolites. The major metabolites were 5-OH-N-Me DBC (50%), N-hydroxymethyl (HMe) DBC (25-30%) and 3-OH-N-Me DBC (10%). Addition of 1,1,1-trichloropropene-2,3-oxide (TCPO) to the standard incubation medium permitted the identification of two dihydrodiols among the minor metabolites. No metabolite of DBC was observed after incubation of N-Me DBC, or its major metabolite N-HMe DBC, with either mouse or rat microsomes, but the possibility of a slight demethylation cannot be totally excluded. The lack of biotransformation at the nitrogen atom site may explain the lack of hepatotoxicity and liver carcinogenic activity of N-Me DBC. The modulation of metabolism by epoxide hydrolase, cytosol and glutathione was also investigated. The results are discussed in the light of data previously obtained with hepatotoxic and hepatocarcinogenic DBC.