Energy metabolism in the cyanobacterium Plectonema boryanum. Participation of the thylakoid photosynthetic electron transfer chain in the dark respiration of NADPH and NADH

The oxidation of NADPH and NADH was studied in the light and in the dark using sonically derived membrane vesicles and osmotically shocked spheroplasts. These two types of cell-free membrane preparations mostly differ in that the cell and thylakoid membranes are scrambled in the former type and that they are more or less separated in the latter type of preparations. In the light, using both kinds of preparations, each of NADPH and NADH donates electrons via the plastoquinone-cytochrome $\text{b}\text{c}$ redox complex (Qbc redox complex) to the thylakoid membrane-bound cytochrome c-553 preoxidized by a light flash and to methylviologen via Photosystem I. NADPH donates electrons to the thylakoid membrane via a weakly rotenone-sensitive dehydrogenase to a site that is situated beyond the 3(3′,4′-dichlorophenyl)-1,1-dimethylurea sensitive site and before plastoquinone. Ferredoxin and easily soluble cytoplasmic proteins are presumably not involved in light-mediated NADPH oxidation. Inhibitors of electron transfer at the Qbc redox complex as the dinitrophenylether of 2-iodo-4-nitrothymol, 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone and 2-n-heptyl-4-hydroxy-quinone-N-oxide are effective, but antimycin A and KCN are not. The oxidation of NADH showed comparable sensitivity to these inhibitors. However, the oxidation of NADH is antimycin-A-sensitive regardless of the kind of membrane preparation used, indicating that in this case electrons are donated to a different site on the thylakoid membrane. In the dark, NADPH and NADH donate electrons at sites that behave similar to those of light-mediated oxidation, indicating that the initial steps of electron transfer are situated at the thylakoid membranes. However, NADPH oxidation is in some cases not sensitive to inhibitors active at the Qbc redox complex. It is concluded that O₂ reduction takes place at two different sites, one partly developed in vitro, situated near the rotenone-sensitive NADPH dehydrogenase, and another, highly KCN-sensitive one, situated beyond the Qbc redox complex and used in vivo. The terminal oxygen-reducing step of NADPH and NADH oxidation in the dark showed a preparation-dependent sensitivity for KCN, more than 80% inhibition in sonically derived membrane vesicles and less than 30% inhibition in osmotically shocked spheroplasts. From this result we tentatively conclude that the highly KCN-sensitive oxidase is not necessarily located at the thylakoid membrane and could be located at the cytoplasmic membrane.     

Potassium accumulation in growing Methanobacterium thermoautotrophicum and its relation to the electrochemical proton gradient

Cultures of Methanobacterium thermoautotrophicum (Marburg) growing on media low in potassium accumulated the cation up to a maximal concentration gradient ([K⁺]_{intracellular}/[K⁺]_{extracellular}) of approximately 50,000-fold. Under these conditions, the membrane potential was determined by measuring the equilibrium distribution of the lipophilic cation (¹⁴C) tetraphenylphosphonium (TPP⁺). This cation was accumulated by the cells 350-to 1,000-fold corresponding to a membrane potential (inside negative) of 170–200 mV. The pH gradient, as measured by equilibrium distribution of the weak acid, benzoic acid, was found to be lower than 0.1 pH units (extracellular pH=6.8). The addition of valinomycin (0.5–1 nmol/mg cells) to the culture reduced the maximal concentration gradient of potassium from 50,000-to approximately 500-fold, without changing the membrane potential. After dissipation of the membrane potential by the addition of ¹²C-TTP⁺ (2 mol/mg cells) or tetrachlorosalicylanilide (3 nmol/mg cells), a rapid and complete efflux of potassium was observed.These data indicate that potassium accumulation in the absence of valinomycin is not in equilibrium with the membrane potential. It is concluded that at low extracellular K⁺ concentrations potassium is not accumulated by M. thermoautotrophicum via an electrogenic uniport mechanism.Non-common abbreviations TPP⁺ Tetra phenylphosphonium bromide - DTE Dithioerythritol - TCS 3,5,3,4-Tetrachlorosalycylanilide     

Interaction of metabolic inhibitors with actin fibrils

Summary The dependence of the arrangement of fibrillar actin in cultured endothelial cells on metabolic conditions was investigated with cellular elements derived from the heart of Xenopus laevis tadpoles. Either primary culture or an established cell line (XTH-2) were used in these studies The metabolic stage of the cells was influenced by inhibiting respiration and lactate production. The actin pattern was revealed either by indirect immunofluorescence or by tetramethylrhodaminyl (TRITC)-phalloidin fluorescence. Total block of energy supply causes in all cases a distinct loss of actin fibrils, while inhibition of respiration alone increases the variability of actin organization. In primary XTH cells but not in XTH-2 cells cyanide disintegrates most of the actin fibres during 3 h of treatment. This effect is independent of the inhibition of respiration, since actin gels prepared from skeletal muscle also undergo destruction in the presence of cyanide. It is concluded that the actin fibrils of the primary cells and the established line behave differently to changing metabolic conditions and to application of KCN.     

Use of proton Nuclear Overhauser Effects for the determination of the conformations of amino acid residues in oligopeptides

The use of the Nuclear Overhauser Effect to determine backbone and side-chain conformations of oligopeptides is discussed. The distance between the H^α proton of a given residue and the amide proton of the following residue depends only on the dihedral angle ψ. A calibration curve is given for the determination of ψ from the Nuclear Overhauser Effect involving these protons. In amino acids with branched side chains, e.g., threonine, isoleucine, and valine, the Nuclear Overhauser Effect involving the H^β proton and the amide proton in either the same or the following residue gives limited information about both χ¹ and either or ψ. The Nuclear Overhauser Effect involving the H^α and H^γ protons in leucine gives information about χ¹ and χ².     

Fatty acid synthesis by isolated chromoplasts from the daffodil. Energy sources and distribution patterns of the acids

1. Fatty acid synthesis in isolated intact chromoplasts from [1-¹⁴C]acetate was made possible by using ATP, ADP (via adenylate kinase), and, with decreasing efficiency, UTP, CTP, and GTP as energy sources. 2. The glycolytic path from dihydroxyacetone phosphate to acetyl-CoA operates within the chromoplasts. The glycolytic intermediates, especially 2-phosphoglycerate and phosphoenolpyruvate, served as very effective energy donors for fatty acid synthesis by phosphorylating the endogenous adenine nucleotide pool. 3. In the presence of exogenous ATP or ADP, appreciable amounts of in vitro formed fatty acids were found as acyl-CoA and subsequent products, mainly phosphatidylcholine. When other energy sources were used most of the acids formed were in the free form, and to a minor extent, in the phosphatidic acid and diacylglycerol fractions. Similar results have recently been reported for spinach chloroplasts (Kleinig and Liedvogel 1979, FEBS Lett.101, 339–342).Abbreviations ATP adenosine triphosphate - ADP adenosine diphosphate - UTP uridine triphosphate - CTP cytidine triphosphate - GTP gnanosine triphosphate     

Quantum yield and rate of formation of the carotenoid triplet state in photosynthetic structures

The formation of the triplet state of carotenoids (detected by an absorption peak at 515 nm) and the photo-oxidation of the primary donor of Photosystem II, P-680 (detected by an absorption increase at 820 nm) have been measured by flash absorption spectroscopy in chloroplasts in which the oxygen evolution was inhibited by treatment with Tris. The amount of each transient form has been followed versus excitation flash intensity (at 590 or 694 nm). At low excitation energy the quantum yield of triplet formation (with the Photosystem II reaction center in the state Q⁻) is about 30% that of P-680 photo-oxidation. The yield of carotenoid triplet formation is higher in the state Q⁻ than in the state Q, in nearly the same proportion as chlorophyll a fluorescence. It is concluded that, for excited chlorophyll a, the relative rates of intersystem crossing to the triplet state and of fluorescence emission are the same in vivo as in organic solvent. At high flash intensity the signal of P-680⁺ completely saturates, whereas that of carotenoid triplet continues to increase.

The rate of triplet-triplet energy transfer from chlorophyll a to carotenoids has been derived from the rise time of the absorption change at 515 nm, in chloroplasts and in several light-harvesting pigment-protein complexes. In all cases the rate is very high, around 8 · 10⁷ s⁻¹ at 294 K. It is about 2–3 times slower at 5 K. The transitory formation of chlorophyll triplet has been verified in two pigment-protein complexes, at 5 K.     

Fluorescence induction in whole leaves: Differentiation between the two leaf sides and adaptation to different light regimes

In a variety of plants, the induction kinetics of chlorophyll fluorescence vary substantially depending on whether measured on the upper or lower side of the same leaf. The responses are comparable to those of plants grown under sun and shade conditions. Leaf morphology appears not to be the primary cause of the differences since inversion of the leaves can lead to reversed fluorescence responses. Fluorescence induction was analyzed in control and inverted leaves, and in one case, in chloroplasts from sun and shade leaves. It is concluded from the data that the major differences between the chloroplasts of the upper and lower leaf side reflect ionic and thylakoidmembrane conformational factors, rather than structural differences. Mg²⁺ flux probably plays a significant role in the adjustment of the thylakoid membrane to high or low light conditions.     

浙北平原水杉人工林生物量的研究

 本文对浙江省北部平原水杉人工林的生物量和生产力进行了测定和研究。按平均标准木法分别调查了干、枝、叶、根的生物量。据调查材料,用相对生长规律建立了估测单株林木各器官干重的回归方程,方程的相关系数和估测精度符合要求,具实用价值。研究结果表明：水杉人工林生物量随年龄的增长而增加,林带18年生后增加速度变缓,片林生物量普遍大于林带生物量,生物量组成比例因年龄而异。随着年龄的增加,年平均净生产量、叶面积指数、光能利用率均逐步加大,至18年生时,上述指标分别为17.51t／ha·a、9.1和0.77%。叶净光合生产率以速生阶段为最大,衰退阶段为最低,当叶净光合生产率急剧下降时,可实施主伐更新。     

Cerebral Metabolic Effects of Monoamine Oxidase Inhibition in Normal and 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine Acutely Treated Monkeys

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces dopaminergic cell death in the substantia nigra pars compacta (SNpc) and clinical parkinsonism in humans and experimental animals. Pretreatment with monoamine oxidase inhibitors prevents this cell death and associated parkinsonism by blocking the oxidation of MPTP to a toxic intermediate. The 2-deoxyglucose method was used to study the acute effects of MPTP in the monkey brain and the effects of monoamine oxidase inhibition on local cerebral glucose utilization in both normal and MPTP-treated monkeys. MPTP administration alone caused a major increase in glucose utilization in the SNpc and smaller increases in some subnuclei within the ventral tegmental area in which eventual dopaminergic cell loss also occurs. Pretreatment with pargyline abolished these metabolic increases, a finding suggesting both that the oxidized product of MPTP generates the metabolic increases and that the increased glucose consumption may contribute to cell toxicity. On the other hand, in most cortical, thalamic, striatal, brainstem, and cerebellar areas MPTP alone caused reductions in glucose utilization, and pargyline failed to prevent these effects. Pargyline alone depressed metabolism in the locus coeruleus and a few other monoaminergic structures.     

Evaluation of actual evapotranspiration of a Quercus ilex L. stand by the Bowen Ratio-Energy Budget method

Actual evapotranspiration from a closed-canopy Quercus ilex L. stand has been estimated by applying the Bowen Ratio-Energy Budget method. Daily water loss was 3.5 mm day^–1, with a peak rate near 0.6 mm hour^–1. The phenomenon of thermal inversion, quite common in mediterranean climates, seemed to play a significant role in reducing evapotranspiration, by promoting dew formation and delaying the establishment of fluxes of latent and sensible heat away from the canopy. Dew, which may form over many hours in the night, appears to be a major sink of available energy in the early morning and may represent a useful water source for stressed foliage. The alternating processes of condensation and evaporation may have a beneficial effect on the closed stand micro-environment.