Occurrence of oscillations in ATP synthesis and hydrolysis in chromatophores of Rhodospirillum rubrum

The conditions under which an oscillatory behaviour is observed during net hydrolysis or synthesis of ATP in chromatophores of Rhodospirillum rubrum FR1 are described. In the case of ATPase the oscillations are observed at low temperature (ca. 11°C) in the dark after an initial transient behaviour. These oscillations are attenuated or disappear by the addition of an uncoupler.Oscillations are also observed during ATP synthesis. At 3°C the oscillations appear spontaneously if photophosphorylation is measured during a sufficiently long time. At 30°C the mere intercalation of a dark period also at 30°C is sufficient to trigger the oscillations in the following light period.Abbreviations Bchl Bacteriochlorophyll - FCCP carbonyl cyanide p-trifluoromethoxyphenyl hydrazone - PMS phenazine methosulfate - TMPD, N,N,N,N tetramethyl-1,4-phenylenediamine Dedicated to Prof. Dr. Gerhart Drews as a homage for his permanent example as hard worker and careful scientist and also for his remarkable human quality     

Noncyclic electron transport in chromatophores from photolithotrophically grown Rhodobacter sulfidophilus

Chromatophores isolated from the marine phototrophic bacterium Rhodobacter sulfidophilus were found to photoreduce NAD with sulfide as the electron donor. The apparent K _m for sulfide was 370 M and the optimal pH was 7.0. The rate of NAD photoreduction in chromatophore suspensions with sulfide as the electron donor (about 7–12 M/h·mol Bchl) was approximately onetenth the rate of sulfide oxidation in whole cell suspensions. NAD photoreduction was inhibited by rotenone, carbonyl cyanide-m-chlorophenylhydrazone, and antimycin A. Sulfide reduced ubiquinone in the dark when added to anaerobic chromatophore suspensions. These results suggest that electron transport from sulfide to NAD involves an initial dark reduction of ubiquinone followed by reverse electron transport from ubiquinol to NAD mediated by NADH dehydrogenase.Abbreviations Bchl bacteriochlorophyll - CCCP carbonyl cyanide-m-chlorophenylhydrazone - MOPS 3(N-morpholino)-propane sulfonate - Uq ubiquinone     

Disappearence of the intracytoplasmic membranes inRhodopseudomonas sphaeroides

The photosynthetic bacterium,Rhodopseudomonas sphaeroides, can be grown phototrophically (light, anaerobiosis), of chemotrophically (dark, aerobiosis). In the first case, it contains intracytoplasmic membranes with photosynthetic pigments. When shifted from phototrophy to chemotrophy these membranes disappear in an unknown fashion. In the present experiment, samples were taken for electron microscopy, cell density and bacteriochlorophyll determinations after shift from phototrophy to chemotrophy. The density of intracytoplasmic vesicles was measured on micrographs. During the first 2h growth is very slow and the ultrastructure remains unaltered. As growth resumes, the vesicles disappear at a rate which implies that they are not incorportated into the cytoplasmic membrane, nor actively digested, but remain intact and become increasingly diluted in the cytoplasm as the culture grows. The size of the vesicles was estimated to about 500 Å. The number of vesicles in phototrophically grown cells was calculated to about 575 per cell, and after 6h chemotrophic growth to about 100. The areas of the cytoplasmic and intracytoplasmic membranes are roughly calculated.Abbreviations Bchl bacteriochlorophyll - CM cytoplasmic membranes - ICM intracytoplasmic membranes     

F0F1-ATPase as biosensor to detect single virus

F(0)F(1)-ATPase within chromatophore was constructed as a biosensor (immuno-rotary biosensor) for the purpose of capturing single virus. Capture of virus was based on antibody-antigen reaction. The detection of virus based on proton flux change driven by ATP-synthesis of F(0)F(1)-ATPase, which was indicated by F1300, was directly observed by a fluorescence microscope. The results demonstrate that the biosensor loading of virus particles has remarkable signal-to-noise ratio (3.8:1) compared to its control at single molecular level, and will be convenient, quick, and even super-sensitive for detecting virus particles.     

Amöboid bewegliche Pigmentzellen im Epithel des Seeigels Centrostephanus longispinus

Zusammenfassung Für den physiologischen Farbwechsel bei Vertebraten und Evertebraten gilt die Vorstellung, daß eine Pigmentbewegung innerhalb einer formkonstanten Zelle stattfindet. Am Seeigel Centrostephanus longispinus wird nun der Nachweis einer amoeboiden Bewegung von Pigmentzellen geführt: Die Epidermis von Centrostephanus enthält große braune Chromatophoren, die bei Belichtung eine Pigmentdispersion, bei Verdunkelung eine Konzentration des Pigments zeigen. Die Chromatophoren sind außerordentlich stark verzweigte Zellen, deren Arme dicht mit Pigmentgrana erfüllt sind. Im geballten Zustand ist die allgemeine Zellform mehr oder weniger ovoid, wobei die Zellarme eingezogen und dicht um die Zellmitte angeordnet sind. Dispersion des Pigments wird hervorgerufen durch Ausstrecken der pigmentierten Zellarme in den Interzellularraum des umgebenden Gewebes. Innerhalb der Zelle werden filamentöse Elemente nachgewiesen, die vermutlich für die Zellbeweglichkeit verantwortlich sind. — Ferner wird der zelluläre Aufbau des Integuments beschrieben.

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Amoeboid pigment cells in the epithelium of the sea urchin Centrostephanus longispinus A novel colour change mechanism

Summary Rapid colour changes in vertebrate and invertebrate species are considered to be due to movement of pigment granules within pigment cells of constant shape. Evidence is presented in this study to show that an amoeboid movement of chromatophores occurs in the epidermis of the Echinoderm Centrostephanus longispinus. The epidermis in this species contains large brown chromatophores, which display a dispersion of pigment on illumination and its concentration on darkening. The chromatophores are extensively branched cells, and their branches are densely packed with pigment granules. In the state of pigment concentration, the shape of the cell is more or less ovoid, and the cell branches are drawn in and closely arranged around the cell centre. Dispersion is attained by a stretching out of the pigmented cell branches into the intercellular spaces of the surrounding tissue. Within the cell, filamentous elements, which may be functional in the motility of the pigment cell, can be demonstrated.—Additionally the cellular composition of the integument is described.

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft. Frl. A. Mikolaczick danken wir für sorgfältige technische Assistenz.     

Hybrid pigment organelles in an invertebrate

Summary Observations of a number of vertebrate chromatophores have revealed the presence of more than one type of pigment organelles, suggesting that the different types are all derived from an equipotential organelle able to differentiate into any of the major pigment-containing organelles (Bagnara, 1972). Observations are presented concerning the occurrence of hybrid pigment inclusions, i.e., all kinds of intergrades between melanosomes, pterinosomes, and reflecting platelets in pigment cells of the daddy-long-legs. It therefore seems possible that pigment organelles in some invertebrates may also be derived from a common pluripotential primordial organelle.Supported from the Deutsche Forschungsgemeinschaft is gratefully acknowledged     

Comparative analyses of the pigment-aggregating and -dispersing actions of MCH on fish chromatophores

In melanophores of the peppered catfish and the Nile tilapia, melanin-concentrating hormone (MCH) at low doses (<1 μM) induced pigment aggregation, and the aggregated state was maintained in the presence of MCH. However, at higher MCH concentrations (such as 1 and 10 μM), pigment aggregation was immediately followed by some re-dispersion, even in the continued presence of MCH, which led to an apparent decrease in aggregation. This pigment-dispersing activity at higher concentrations of MCH required extracellular Ca²⁺ ions. By contrast, medaka melanophores responded to MCH only by pigment aggregation, even at the highest concentration employed (10 μM). Since it is known that medaka melanophores possess specific receptors for α-melanophore-stimulating hormone (α-MSH), the possibility that interaction between MSH receptors and MCH at high doses in the presence of Ca²⁺ might cause pigment dispersion is ruled out. Cyclic MCH analogs, MCH (1–14) and MCH (5–17), failed to induce pigment dispersion, whereas they induced aggregation of melanin granules. These results suggest that another type of MCH receptor that mediates pigment dispersion is present in catfish and tilapia melanophores, and that intact MCH may be the only molecule that can bind to these receptors. Determinations of cAMP content in melanophores, which were isolated from the skin of three fish species and treated with 10 nM or 10 μM MCH, indicate that MCH receptors mediating aggregation may be coupled with Gi protein, whereas MCH receptors that mediate dispersion may be linked to Gs. The response of erythrophores, xanthophores and leucophores to MCH at various concentrations was also examined, and the results suggest that the distribution patterns of the two types of MCH receptors may differ among fish species and among types of chromatophore in the same fish.     

Generation of semiquinone-[2Fe-2S]+ spin-coupled center at the Qo site of cytochrome bc1 in redox-poised,illuminated photosynthetic membranes from Rhodobacter capsulatus

One of the less understood parts of the catalytic cycle of cytochrome bc₁/b₆f complexes is the mechanism of electronic bifurcation occurring within the hydroquinone oxidation site (Q_o site). Several models describing this mechanism invoke a phenomenon of formation of an unstable semiquinone. Recent studies with isolated cytochrome bc₁ or b₆f revealed that a relatively stable semiquinone spin-coupled to the reduced Rieske cluster (SQ-FeS) is generated at the Q_o site during the oxidation of ubi- or plastohydroquinone analogs under conditions of continuous turnover. Here, we identified the EPR transition of SQ-FeS formed upon oxidation of ubihydroquinone in native photosynthetic membranes from purple bacterium Rhodobacter capsulatus. We observed a significant amount of SQ-FeS generated when the antimycin-inhibited enzyme experiences conditions of non-equilibrium caused by the continuous light activation of the reaction center. We also noted that SQ-FeS cannot be detected under equilibrium redox titrations in dark. The non-equilibrium redox titrations of SQ-FeS indicate that this center has a higher apparent redox midpoint potential when compared to the redox midpoint potential of the quinone pool. This suggests that SQ-FeS is stabilized, which corroborates a recently proposed mechanism in which the SQ-FeS state is metastable and functions to safely hold electrons at the local energy minimum during the oxidation of ubihydroquinone and limits superoxide formation. Our results open new possibilities to study the formation and properties of this state in cytochromes bc under close to physiological conditions in which non-equilibrium is attained by the light activation of bacterial reaction centers or photosystems.     

The phosphate-pyrophosphate exchange and hydrolytic reactions of the membrane-bound pyrophosphatase ofRhodospirillum rubrum: Effects of pH and divalent cations

The relation that exist between the Pi-PPi exchange reaction and pyrophosphate hydrolysis by the membrane-bound pyrophosphatase of chromatophores ofRhodospirillum rubrum was studied. The two reactions have a markedly different requirement for pH. The optimal pH for hydrolysis was 6.5 while the Pi-PPi exchange reaction was at 7.5; the pH affects mainly theK _m of Mg²⁺ or Pi for the enzyme; Mn²⁺ and Co²⁺ support the Pi-PPi exchange reaction partially (50%), but the reaction is slower than with Mg²⁺; other divalent cations like Zn²⁺ or Ca²⁺ do not support the exchange reaction. In the hydrolytic reaction, Zn²⁺, at low concentration, substitutes for Mg²⁺ as substrate, and Co²⁺ also substitutes in limited amount (50%). Other cations (Ca²⁺, Cu²⁺, Fe²⁺, etc.) do not act as substrates in complex with PPi. The Zn²⁺ at high concentrations inhibited the hydrolytic reaction, probably due to uncomplexed free Zn²⁺. In the presence of high concentration of substrate for the hydrolysis (Mg-PPi) the divalent cations are inhibitory in the following order: Zn²⁺>Mn²⁺>Ca²⁺Co²⁺>Fe²⁺>Cu²⁺>Mg²⁺. The data in this work suggest that H⁺ and divalent cations in their free form induced changes in the kinetic properties of the enzyme.     

Ultrastructural changes in the dermal chromatophore unit of Hyla arborea during color change

Summary The structural changes in the chromatophores of Hyla arborea related to changes in skin color were studied by electron microscopy and reflectance microspectrophotometry. During a change from a light to a darker green color, the melanosomes of the melanophores disperse and finally surround the iridophores and partly the xanthophores. The iridophores change from cup-shape to a cylindrical or conical shape with a simultaneous change in the orientation of the platelets from being parallel to the upper surface of the iridophores to being more irregular. The xanthophores change from lens-shape to plate-shape. The color change from green to grey seems always to go through a transitional black-green or dark olive green to dark grey. During this change the xanthophores migrate down between the iridophores, and in grey skins they are sometimes found beneath them. The pterinosomes gather in the periphery of the cell, while the carotenoid vesicles aggregate around the nucleus. The iridophores in grey skin are almost ball-shaped with concentric layers of platelets. A lighter grey color arises from a darker grey by an aggregation of melanosomes. The chromatophore values previously defined for Hyla cinerea are applicable in Hyla arborea, and the ultrastructural studies support the assumptions previously made to explain these values.The author wishes to thank Drs. P. Budtz, J. Dyck and L.O. Larsen for valuable discussions and J. Dyck for kindly providing the spectrophotometer granted him by the Danish National Science Foundation. The skilled technical assistance of Mrs. E. Schiøtt Hansen is gratefully acknowledged. Permission was granted by the Springer-Verlag to republish the illustrations of W.J. Schmidt (1920)