Electron acceptors associated with P-700 in Triton solubilized Photosystem I particles from spinach chloroplasts

Flash-induced absorption changes of Triton-solubilized Photosystem I particles from spinach were studied under reducing and/or illumination conditions that serve to alter the state of bound electron acceptors. By monitoring the decay of P-700 following each of a train of flashes, we found that P-430 or components resembling it can hold 2 equivalents of electrons transferred upon successive illuminations. This requires the presence of a good electron donor, reduced phenazine methosulfate or neutral red, otherwise the back reaction of P-700⁺ with P-430 occurs in about 30 ms. If the two P-430 sites, designated Centers A and B, are first reduced by preilluminating flashes or chemically by dithionite under anaerobic conditions, then subsequent laser flashes generate a 250 μs back reaction of P-700⁺, which we associate with a more primary electron acceptor A₂. In turn, when A₂ is reduced by background (continuous) illumination in presence of neutral red and under strongly reducing conditions, laser flashes then produce a much faster (3 μs) back reaction at wavelengths characteristic of P-700. We associate this with another more primary electron acceptor, A₁, which functions very close to P-700. The organization of these components probably corresponds to the sequence $\text{P-700-}\text{A}{}_1\text{-}\text{A}{}_2\text{-P-430[}\text{A}\text{B}\text{]}$. The relation of the optical components to acceptor species detected by EPR, by electron-spin polarization or in terms of peptide components of Photosystem I is discussed.Preliminary experiments with broken chloroplasts suggest that an analogous situation occurs there, as well.     

A flash photolysis ESR study of photosystem II signal IIvf, the physiological donor to P-680+.

In flash-illuminated, oxygen-evolving spinach chloroplasts and green algae, a free radical transient has been observed with spectral parameters similar to those of Signal II (g approximately 2.0045, deltaHpp approximately 19G). However, in contrast with ESR Signal II, the transient radical does not readily saturate even at microwave power levels of 200 mW. This species is formed most efficiently with "red" illumination (lambda less than 680 nm) and occurs stoichiometrically in a 1:1 ratio with P-700+. The Photosystem II transient is formed in less than 100 mus and decays via first-order kinetics with a halftime of 400-900 mus. Additionally, the t1/2 for radical decay is temperature independent between 20 and 4 degrees C; however, below 4 degrees C the transient signal exhibits Arrhenius behavior with an activation energy of approx. 10 kcal-mol-1. Inhibition of electron transport through Photosystem II by o-phenanthroline, 3-(3,4-dichlorophenyl)-1,1-dimethylurea or reduced 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone suppresses the formation of the light-induced transient. At low concentrations (0.2 mM), 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone partially inhibits the free radical formation, however, the decay kinetics are unaltered. High concentrations of 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (1-5 mM) restore both the transient signal and electron flow through Photosystem II. These findings suggest that this "quinoidal" type ESR transient functions as the physiological donor to the oxidized reaction center chlorophyll, P-680+.     

Global classification of natural terrestrial ecosystems

Summary A global classification system of natural terrestrial ecosystems (including systematic notation), based on the climate zones of Walter, is presented. The basic units of the system are the ecological units biome and biogeocoene. The zonobiomes, which are climate zones corresponding to the largest vegetation units, are subdivided into subzonobiomes and these into individual biomes. The biomes are thus natural, geographical units within the climate zones. They are in turn subdivided into individual biogeocoenes and their constituent synusiae. In addition, the coordinate concepts of pedobiome and orobiome are introduced. These are distinguished from the zonobiomes as follows:1. the pedobiomes by extreme edaphic conditions which cause azonal vegetation.2. the orobiomes, as mountain ranges, by their vertical climate zonation and the altitudinal belts of vegetation.These relationships are explained, and two subseries of pedo-and oro-subunits are established. Transitional zones (zono-ecotones) between individual zonobiomes are also distinguished. The classification system is summarized in a schematic, and a world map of zonobiomes and zono-ecotones is included. More details are presented in Walter (1976).

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Zusammenfassung Ein globales Gliederungssystem der natürlichen terrestrischen Ökosysteme (einschließlich systematischen Bezeichnungen) wird in Beziehung zu den Walter'schen Klimazonen gesetzt. Grundeinheiten des Systems sind die ökologischen Einheiten Biom und Biogeozön. Die Zonobiome werden unterteilt in Subzonobiome und diese in Biome. Die Zonobiome sind Klimazonen und entsprechen den größten Vegetationseinheiten. Die Biome sind natürliche, geographische Einheiten innerhalb der Klimazonen. Sie werden bis zu einzelnen Biogeozönen und ihren Synusien (Teilsytemen) unterteilt. Parallel dazu werden die Begriffe Pedobiom und Orobiom eingeführt. Diese heben sich aus den Zonobiomen heraus: die Pedobiomen durch extreme Böden, die eine azonale Vegetation bedingen, die Orobiome als Gebirge durch die vertikale Klimagliederung und die Höhenstufen der Vegetation. Diese Beziehungen werden erklärt, und zwei Nebenreihen der Pedo- bzw. Orobiom-Untereinheiten werden aufgestellt. Zwischen den einzelnen Zonobiomen werden Übergangszonen (Zonoökotone) unterschieden. Das Gliederungssytem wird bereits in einem Schema zusammengefaßt, und eine Weltkarte der Zonobiome und Zonoökotone wird beigefügt. Ausführlich werden alle diese Fragen bei WALTER (1976) behandelt.

     

Possible role in uptake of water vapour by ixodid tick salivary glands

The mouth is confirmed as the site of water vapor uptake in the lone star tick, Amblyomma americanum. It was shown that the level of chloride (³⁶Cl) increased in the mouthparts of desiccated ticks. The highest levels of ³⁶Cl were found in the mouthparts, salivary glands, and gut tissue during rehydration. It is suggested that ions are secreted by the salivary glands into the mouth where water is picked up hygroscopically by the secretion. It is further suggested that the water and ions are then swallowed and absorbed from the lumen of the gut.     

Mathematical analysis of multienzyme systems. II. Steady state and transient control.

The control theory of steady states, previously presented for linear enzymatic systems (Heinrich and Rapoport, 1974) is extended to nonlinear systems. On the basis of three theorems a new procedure for the calculation of the control strength and of the control matrix is developed. The theory is applied to the extended model of glycolysis of erythrocytes, which includes also ATP-consuming processes. Also in this model the glycolytic flux is mainly controlled by the hexokinase-phosphofructokinase-system. The control strengths of the pyruvate kinase and of the enzymes of the 2.3 P2G-bypass are negligibly small. The control strength of the ATPase is negative, i.e. an activation of this enzyme leads to a decrease of the flux. For transition states of multienzyme systems definitions are given for the mean time required for the transition of the metabolites and for the "transient control" of enzymes. Enzymes with a pronounced influence on the transition time are called time-limiting enzymes. Enzymes which excert strong control on the time-dependent processes may have little influence under steady state conditions and vice versa. The transition times of ATP have been calculated for transient states of glycolysis.     

Beiträge zur Vitalfärbung von Pilzmyzelien II

Ohne ZusammenfassungBeitr. z. Vitalf. v. Pilzmyzelien I; Flora134, S. 58, 1939.     

Effect of indomethacin on hepatic glucose production in vitro: the impact of hepatic glycogen content

The effect of indomethacin (IND) on glucagon-induced hepatic glucose production (HGP) was studied in the isolated perfused livers of rats. Addition of IND (0.2 mM) to the perfusion medium had no effect on glucagon-stimulated HGP when compared to control experiments without added IND (1.02 +/- 0.17 vs. 1.00 +/- 0.26 mmol per (120 min X 100 g b.w.), respectively; NS). Intravenous pretreatment with both, IND (10 mg/kg b.w.), or vehicle resulted in a reduction in glucagon-induced HGP due to a decrease in hepatic glycogen content. A complete depletion of the hepatic glycogen pool and thus a lack in glucagon-stimulated HGP was observed when IND was given intraperitoneally. These results indicate that the changes in HGP observed after pretreatment with IND may largely if not completely be due to a non-specific depletion in hepatic glycogen content and that IND does not exert a direct influence on HGP.