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PubMed1974

Topology and growth of the intracytoplasmic membrane system of Rhodopseudomonas spheroides: protein, chlorophyll, and phospholipid insertion into steady-state anaerobic cells.

An equilibrium density gradient centrifugation study involving the separation of "old" and "new" membranes has been developed to determine the manner in which protein, lipid, and chlorophyll are incorporated into growing intracytoplasmic membranes (chromatophores) of Rhodopseudomonas spheroides. Chromatophores derived from cells grown in an H(2)O-medium had a density of 1.175 to 1.180 g/cm(3) and were readily separable from chromatophores having a density of 1.220 to 1.230 isolated from cells grown in a 70% D(2)O-medium. After a shift from "D(2)O-" to "H(2)O"-based media, only hybrid chromatophores derived from a combination of "heavy" (old) and "light" (new) chromatophore material could be detected. The experimentally determined, median density values for the growing intracytoplasmic membrane system followed a theoretically determined profile which was calculated from the density of full "heavy" and full "light" material assuming random, homogeneous incorporation of new material into old membrane. The distribution of the radioactive labels for protein (leucine) and chlorophyll (delta-aminolevulinic acid) were identical and showed a reproducible displacement of the "old" material to the heavy side of the optical density at 365 nm (OD(365)) absorbance and a displacement of the "new" material to the light side of the OD(365) absorbance profile. Specific phospholipid growth showed no displacement for either the "old" or "new" material from the median absorbance profile.

Acetates↗

PubMed1986

Role of apparent membrane growth initiation sites during photosynthetic membrane development in synchronously dividing Rhodopseudomonas sphaeroides.

Sites of intracytoplasmic membrane growth and temporal relations in the assembly of photosynthetic units were examined in synchronously dividing Rhodopseudomonas sphaeroides cells. After rate-zone sedimentation of cell-free extracts, apparent sites of initiation of intracytoplasmic membrane growth formed an upper pigmented band that sedimented more slowly than the intracytoplasmic membrane-derived chromatophore fraction. Throughout the cell cycle, the levels of the peripheral B800-850 light-harvesting pigment-protein complex relative to those of the core B875 complex in the upper pigmented fraction were only about half those of chromatophores. Pulse-labeling studies with L-[35S]methionine indicated that the rates of assembly of proteins in the upper pigmented fraction were much higher than those of chromatophores throughout the cell cycle; rates for the reaction center polypeptides were estimated to be approximately 3.5-fold higher than in chromatophores when the two membrane fractions were equalized on a protein basis. In pulse-chase studies, radioactivity of the reaction center and B875 polypeptides increased significantly in chromatophores and decreased in the upper pigmented band during cell division. These data suggest that the B875 reaction center cores of the photosynthetic units are inserted preferentially into sites of membrane growth initiation isolated in the upper pigmented band and that the incomplete photosynthetic units are transferred from their sites of assembly into the intracytoplasmic membrane during cell division. These results suggested further that B800-850 is added directly to the intracytoplasmic membrane throughout the cell cycle.

Bacterial Chromatophores↗

PubMed1989

Division of divalent cations into two groups in relation to their effect on the coupling of the F0F1-ATPase of Rhodospirillum rubrum to the protonmotive force.

Divalent cations are divided into two groups in relation to their ability to promote ATP synthase catalyzed reactions. In the presence of Mg2+, the following pattern rules: (i) uncoupler-stimulated ATP hydrolysis of Rhodospirillum rubrum chromatophores which shows an optimum concentration of the divalent cation; (ii) ATP-induced proton pumping in chromatophores; (iii) light-induced ATP synthesis in chromatophores; (iv) no or very low ATPase activity of purified F1-ATPase unmasked by diethylstilbestrol or n-octyl beta-D-glucopyranoside. In the presence of Ca2+, the following pattern occurs: (i) no stimulation of the ATP hydrolysis in chromatophores by carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone; (ii) no ATP-induced proton pumping; (iii) no light-induced ATP synthesis; (iv) a high ATPase activity of the purified F1-ATPase which is inhibited by diethylstilbestrol and n-octyl beta-D-glucopyranoside. Co2+, Mn2+, and Zn2+ are members of the "Mg2+-group", whereas Cd2+ is suggested to fall between the two groups. Intrinsic uncoupling of the membrane-bound ATP synthase has been suggested to account for the effect caused by Ca2+ in chloroplasts [Pick, U., & Weiss, M. (1988) Eur. J. Biochem. 173, 623-628]. Such an interpretation is consistent with our results on chromatophores. The uncoupling cannot occur at the level of the membrane since neither light-induced nor Mg-ATP-induced proton pumping is affected by Ca2+. A conformational change is suggested to be the reason for this intrinsic uncoupling, and it is proposed to be controlled by the diameters of the divalent cations (Ca2+ greater than Cd2+ greater than Mn2+ greater than Co2+ greater than Zn2+ greater than Mg2+).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗

PubMed1986

Orthophosphate-pyrophosphate exchange catalyzed by soluble and membrane-bound inorganic pyrophosphatases. Role of H+ gradient.

A comparative study of the orthophosphate-pyrophosphate exchange reaction catalyzed by the soluble pyrophosphatase from baker's yeast and by the membrane-bound pyrophosphatase of Rhodospirillum rubrum chromatophores was performed. In both systems the rate of exchange increased when the pH of the medium was raised from 6.0 to 7.8 and when the MgCl2 concentration was raised from 0.1 mM to 20 mM. For the yeast pyrophosphatase the exchange rates measured at different pH values and in the presence of 6.7 to 8.8 mM free Mg2+ superimposed as a single curve when plotted as a function of the concentrations of either HPO4(2-) or MgHPO4. This was not observed with the use of R. rubrum chromatophores. With yeast pyrophosphatase, the Km for Pi was higher than 10 mM and could not be measured when the free Mg2+ concentration in the medium was lower than 0.5 mM. There was a decrease in the Km for Pi when the free Mg2+ concentration was raised to 6.7-8.8 mM or when, in the presence of low free Mg2+, the organic solvents dimethylsulfoxide (20% v/v) or ethyleneglycol (40% v/v) were included in the assay medium. In the presence of 6.7-8.8 mM free Mg2+ the Km for total Pi was 7 mM at pH 7.0 and 12 mM at pH 7.8. For the ionic species HPO4(2-) and MgHPO4, the Km values were 5.8 mM and 4.2 mM respectively. In the presence of 0.24-0.42 mM free Mg2+ and either 20% (v/v) dimethylsulfoxide or 40% (v/v) ethyleneglycol the Km values for total Pi, HPO4(2-) and MgHPO4 were 7.6, 3.5 and 0.5 mM respectively. With R. rubrum chromatophores, the Km for Pi in the presence of 5.5-7.5 mM free Mg2+ was very high and could not be measured. In the presence of 0.24-0.45 mM free Mg2+ the ratio between the velocities of hydrolysis and synthesis of pyrophosphate measured at pH 7.8 with yeast pyrophosphatase and chromatophores of R. rubrum were practically the same. When the free Mg2+ concentration was raised to 5.5-8.8 mM this ratio decreased from 1028 to 540 when the yeast pyrophosphatase was used and from 754 to 46 when chromatophores were used.

Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone↗

PubMed1994

GRAVITY AND LIGHT INFLUENCE THE COUNTERSHADING REFLEXES OF THE CUTTLEFISH SEPIA OFFICINALIS

Rotation (roll or pitch) of a cuttlefish away from its normal orientation produces countershading reflexes (CSRs) that consist of chromatophore expansion on the ventral body surface. When rotation is in the roll plane, the CSR has two components on each side of the body. The first (component A) consists of a unilateral expansion of chromatophores on the uppermost latero-ventral edge of the mantle, the underside of the upper fin and the uppermost side of the head; it occurs when the angle of rotation is less than 90°. Further rotation (from approximately 90° to approximately 180°) adds the second component (component B): a unilateral expansion of the chromatophores on the upper half of the ventral surface of the mantle, funnel, head and arms. When rotation is in the pitch plane, chromatophores expand on the posterior part of the ventral mantle and fins when the head is down; when the head is up, chromatophores expand on the ventral surface of the arms, head and funnel and on the anterior part of the ventral mantle and fins. The pitch CSR is always bilateral. Destruction of the gravity or the angular acceleration receptor systems of the statocysts demonstrates that it is the gravity receptor systems that drive the CSRs. Unilateral destruction of the gravity receptor systems shows that the pitch CSR is driven bilaterally, whereas the roll CSR is driven unilaterally. Components A and B of the roll CSR are driven by input from the ipsilateral statocyst, but component A is additionally driven by light. Brain lesions provide evidence that the pathways for the CSRs run through the lateral basal lobes in the supraoesophageal part of the brain.

Journal Article↗

PubMed2002

Morphological studies on the mechanisms of pigmentary organelle transport in fish xanthophores and melanophores.

Pigmentary organelle translocations within fish chromatophores undergo physiological color changes when exposed to external signals. Chromatophores can be isolated in high yields, and their pigmentary organelles can be tracked readily by microscopy. The combined efforts of morphology and biomolecular chemistry have led to the identification of and determination of the interrelationships between cytoskeletal elements and accessory proteins, motor molecules, cytomatrix, and pigmentary organelles of various sizes. Fish chromatophores have been classified as fast, intermediate, and slow translocators, based on the relative numbers of microtubules. Studies on cultured goldfish (Carassius auratus L.) xanthophores for over 20 years have demonstrated that in this slow translocator, tubulovesicular structures of the smooth endoplasmic reticular (SER) cisternae are involved in the disperson and aggregation of associated carotenoid droplets (CD) with some involvement of cytoskeletal elements. Killifish (Fundulus heteroclitus L.) melanophore, a fast translocator, was also examined. Recent work demonstrates a bright fluorescent "starburst"-like spot that we call an actin filament-organizing center (AFOC) with radiating microfilaments, akin to the microtubule-organizing center (MTOC) with radiating microtubules. Melanosomes translocate single-file on microtubules and are not associated with SER cisternae. Slower CD dispersion or aggregation in goldfish xanthophores seems to be predominantly microfilament-based transport, or microfilament- and microtubule-based transport, respectively. Faster melanosome translocations in killifish melanophores are based on microtubules, with our evidence indicating microfilament involvement. Neural crest-derived chromatophores are models for vesicular transport in axons, and immunocytochemical and imaging technologies may help to elucidate the cellular transport mechanisms.

Animals↗

PubMed2005

The influence of long-term chromatic adaptation on pigment cells and striped pigment patterns in the skin of the zebrafish, Danio rerio.

The striped pigment patterns in the flanks of zebrafish result from chromatophores deep within the dermis or hypodermis, while superficial melanophores associated with dermal scales add a dark tint to the dorsal coloration. The responses of these chromatophores were compared during the long-term adaptation of zebrafish to a white or a black background. In superficial skin, melanophores, xanthophores, and two types of iridophores are distributed in a gradient along the dorso-ventral axis independent of the hypodermal pigment patterns. Within one week the superficial melanophores and iridophores changed their density and/or areas of distribution, which adopted the dorsal skin color and the hue of the flank to the background, but did not affect the striped pattern. The increases or decreases in superficial melanophores are thought to be caused by apoptosis or by differentiation, respectively. When the adaptation period was prolonged for more than several months, the striped color pattern was also affected by changes in the width of the black stripes. Some black stripes disappeared and interstripe areas were emphasized with a yellow color within one year on a white background. Such long-term alteration in the pigment pattern was caused by a decrease in the distribution of melanophores and a concomitant increase in xanthophores in the hypodermis. These results indicate that morphological responses of superficial chromatophores contribute to the effective and rapid background adaptation of dorsal skin and while prolonged adaptation also affects hypodermal chromatophores in the flank to alter the striped pigment patterns.

Adaptation, Physiological↗

PubMed1975

Cytochrome b and photosynthetic sulfur bacteria.

Chromatophores isolated from the purple sulfur bacterium Chromatium and the green sulfur bacterium Chlorobium exhibit absorbance changes in the cytochrome alpha-band region consistent with the presence of a b-type cytochrome. Cytochrome content determined by reduced minus oxidized difference spectra and by heme photochemically active bacteriochlorophyll (reaction-center bacteriochlorophyll). The b-type cytochrome in Chromatium has an alpha-band maximum at 560 nm and a midpoint oxidation-reduction potential of -5 mV at pH 8.0. The b-type cytochrome in Chlorobium has an alpha-band maximum at 564 nm and an apparent midpoint oxidation-reduction potential near -90 mV. Chromatophores isolated from both Chromatium and Chlorobium cells catalyze a photoreduction of cytochrome b that is enhanced in the presence of antimycin A. Antimycin A and 2-n-heptyl-4-hydroxyquinoline-N-oxide inhibit endogenous (but not phenazine methosulfate-mediated) cyclic photophosphorylation in Chromatium chromatophores and non-cyclic electron flow from Na-2S to NADP in Chlorobium chromatophores. These observations suggest that b-type cytochromes may function in electron transport reactions in photosynthetic sulfur bacteria.

Antimycin A↗

PubMed1976

Orientation of chromophores in reaction centers of Rhodopseudomonas sphaeroides. Evidence for two absorption bands of the dimeric primary electron donor.

Chromatophores from Rhodopseudomonas sphaeroides were oriented by allowing aqueous suspensions to dry on glass plates. Orientation of reaction center pigments was investigated by studying the linear dichroism of chromatophores in which the absorption by antenna bacteriochlorophyll had been attenuated through selective oxidation. Alternatively the light-induced absorbance changes, in the ranges 550-650 and 700-950nm, were studied in untreated chromatophores. The long wave transition moment of reaction center bacteriochlorophyll (P-870) was found to be nearly parallel to the plane of the membrane, whereas the long wave transition moments of bacteriopheophytin are polarized out of this plane. For light-induced changes the linear dichroic ratios, defined as deltaav/deltaah, are nearly the same for untreated and for oxidized chromatophores. Typical values are 1.60 at 870 nm, 0.80 at 810nm, 1.20 at 790 nm, 0.70 at 765 nm, 0.30 at 745 nm , and 0.50 at 600 nm. The different values for the absorbance decrease at 810 nm (0.80) and the increase at 790 nm (1.20) are incompatible with the hypothesis that these changes are due to the blue-shift of a single band. We propose that the decreases at 870 and 810 nm reflect bleaching of the two components of a bacteriochlorophyll dimer, the "special pair" that shares in the photochemical donation of a single electron. The increase at 790 nm then represents the appearance of a monomer band in place of the dimer spectrum, as a result of electron donation. This hypothesis is consistent with available data on circular dichroism. It is confirmed by the presence of a shoulder at 810 nm in the absorption spectrum of reaction centers at low temperature; this band disappears upon photooxidation of the reaction centers. For the changes near 760 nm, associated with bacteriopheophytin, the polarization and the shape of the "light-dark" difference spectrum (identical to the first derivative of the absorption spectrum) show that the 760 nm band undergoes a light-induced shift to greater wavelengths.

Bacterial Chromatophores↗

PubMed1997

The reduction of acetylpyridine adenine dinucleotide by NADH: is it a significant reaction of proton-translocating transhydrogenase, or an artefact?

Transhydrogenase is a proton pump. It has separate binding sites for NAD+/NADH (on domain I of the protein) and for NADP+/NADPH (on domain III). Purified, detergent-dispersed transhydrogenase from Escherichia coli catalyses the reduction of the NAD+ analogue, acetylpyridine adenine dinucleotide (AcPdAD+), by NADH at a slow rate in the absence of added NADP+ or NADPH. Although it is slow, this reaction is surprising, since transhydrogenase is generally thought to catalyse hydride transfer between NAD(H)--or its analogues and NADP(H)--or its analogues, by a ternary complex mechanism. It is shown that hydride transfer occurs between the 4A position on the nicotinamide ring of NADH and the 4A position of AcPdAD+. On the basis of the known stereospecificity of the enzyme, this eliminates the possibilities of transhydrogenation(a) from NADH in domain I to AcPdAD+ wrongly located in domain III; and (b) from NADH wrongly located in domain III to AcPdAD+ in domain I. In the presence of low concentrations of added NADP+ or NADPH, detergent-dispersed E. coli transhydrogenase catalyses the very rapid reduction of AcPdAD+ by NADH. This reaction is cyclic; it takes place via the alternate oxidation of NADPH by AcPdAD+ and the reduction of NADP+ by NADH, while the NADPH and NADP+ remain tightly bound to the enzyme. In the present work, it is shown that the rate of the cyclic reaction and the rate of reduction of AcPdAD+ by NADH in the absence of added NADP+/NADPH, have similar dependences on pH and on MgSO4 concentration and that they have a similar kinetic character. It is therefore suggested that the reduction of AcPdAD+ by NADH is actually a cyclic reaction operating, either with tightly bound NADP+/NADPH on a small fraction (< 5%) of the enzyme, or with NAD+/NADH (or AcPdAD+/AcPdADH) unnaturally occluded within the domain III site. Transhydrogenase associated with membrane vesicles (chromatophores) of Rhodospirillum rubrum also catalyses the reduction of AcPdAD+ by NADH in the absence of added NADP+/NADPH. When the chromatophores were stripped of transhydrogenase domain I, that reaction was lost in parallel with 'normal reverse' transhydrogenation (e.g., the reduction of AcPdAD+ by NADPH). The two reactions were fully recovered upon reconstitution with recombinant domain I protein. However, after repeated washing of the domain I-depleted chromatophores, reverse transhydrogenation activity (when assayed in the presence of domain I) was retained, whereas the reduction of AcPdAD+ by NADH declined in activity. Addition of low concentrations of NADP+ or NADPH always supported the same high rate of the NADH-->AcPdAD+ reaction independently of how often the membranes were washed. It is concluded that, as with the purified E. coli enzyme, the reduction of AcPdAD+ by NADH in chromatophores is a cyclic reaction involving nucleotides that are tightly bound in the domain III site of transhydrogenase. However, in the case of R. rubrum membranes it can be shown with some certainty that the bound nucleotides are NADP+ or NADPH. The data are thus adequately explained without recourse to suggestions of multiple nucleotide-binding sites on transhydrogenase.

Binding Sites↗

PubMed1980

Localization of photosynthetic membrane components in Rhodopseudomonas sphaeroides by a radioactive labeling procedure.

Reduction with [3H]KBH4 of Schiff's bases generated by reaction with pyridoxal 5'-phosphate (which cannot penetrate the intact cytoplasmic membrane) yields tritium-labeled derivatives of both proteins and lipids accessible on the periplasmic side of the cytoplasmic membrane. Application of this technique to phototrophically grown Rhodopseudomonas sphaeroides labeled both the cell envelope and chromatophore fractions. The technique was also applied to R. sphaeroides harvested at various times during an adaptation from heterotrophic to phototrophic growth conditions. The specific activity of the chromatophore fraction after 20 h of adaptation was 76% of that found at the beginning, indicating that the intracytoplasmic membranes and cytoplasmic membrane form a continuous membrane system, with the majority of the intracytoplasmic membranes accessible to the external medium throughout the adaptation. The identity of the proteins labeled by this technique was investigated in two fractions labeled after cell disruption: normal "inside-out" chromatophores and "right-side-out" membrane vesicles isolated by lysozyme--osmotic shock treatment of cells grown in high light intensity (15000 lx). The results after sodium dodecyl sulfate--polyacrylamide gel electrophoresis and fluorography indicated that the 28000-dalton subunit (and to a lesser extent the 21000-dalton subunit) of the reaction center complex and two polypeptides in the light-harvesting region of the gel were heavily labeled in the chromatophores and were thus accessible on the cytoplasmic side of the membrane. At least one of the latter two polypeptides was also labeled in the membrane vesicles and was thus also accessible on the periplasmic side of the membrane. None of the reaction center subunits was significantly labeled in a reaction center complex prepared from the membrane vesicle sample.

Bacterial Chromatophores↗

PubMed1969

Multiple light-induced reactions of cytochromes b and c in Rhodopseudomonas spheroides.

Illumination of chromatophore preparations from Rhodopseudomonas spheroides causes the oxidation of a cytochrome c and a slight oxidation of a cytochrome b with a maximum at 560nm. When illuminated in the presence of antimycin A the oxidation of cytochrome c was more pronounced and cytochrome b(560) was reduced; the dark oxidation of cytochrome b(560) was biphasic in the presence of succinate, but not in the presence of NADH, a less effective reductant. Split-beam spectroscopy showed that, in addition to the reduction of cytochrome b(560), another pigment with maxima at 565 and 537nm. was reduced and was more rapidly oxidized in the dark than cytochrome b(560). This pigment, tentatively identified as cytochrome b(565), was also detected in spectra at 77 degrees k, after brief illumination at room temperature; the maxima at 77 degrees k were at 562 and 536nm. In the absence of antimycin A, light caused a transient reduction of cytochrome b(565) and an oxidation of cytochrome b(560). Dark oxidation of b(565) was rapid, even in the presence of antimycin A and succinate. Difference spectra, at 77 degrees k, of ascorbate-reduced minus succinate-reduced chromatophores or of anaerobic succinate-reduced minus aerobic succinate-reduced chromatophores suggested that two cytochromes c were present, with maxima at 547 and 549nm. When chromatophores frozen at 77 degrees k were illuminated both these cytochromes c were oxidized, indicating a close association with the photochemical reaction centre. A scheme involving two reaction centres is proposed to explain these results.

Antimycin A↗

PubMed2004

Somatolactin selectively regulates proliferation and morphogenesis of neural-crest derived pigment cells in medaka.

Species-specific colors and patterns on animal body surfaces are determined primarily by neural-crest-derived pigment cells in the skin (chromatophores). However, even closely related species display widely differing patterns. These contrasting aspects of chromatophores (i.e., the fixed developmental control within species and extreme diversity among species) seem to be a curious and suitable subject for understanding evolution and diversity of organisms. Here we identify a gene responsible for medaka "color interfere" mutants by positional cloning. These mutants do not show any obvious morphological and physiological defects other than defects in chromatophore proliferation and morphogenesis. The mutation has been identified as an 11-base deletion in somatolactin, which causes truncation 91 aa upstream of the C terminus of the protein's 230 aa. Somatolactin transcription changed dramatically during morphological body color adaptation to different backgrounds. This genetic evidence explains somatolactin function. Studying this mutant will provide further insights into the development and regulation of chromatophores and clues for reassessing other functions of somatolactin suggested in other fish.

Adaptation, Physiological↗

PubMed1975

Effects of pH indicators on various activities of chromatophroes of Rhodospirillum rubrum.

1. The effects of pH indicators on activities for ATP hydrolysis in the dark and ATP-Pi exchange in the dark were examined with chromatophores from Rhodospirillum rubrum. Of thirty-one pH indicators tested, eleven (metanil yellow, 2, 4-dinitrophenol, ethyl orange, bromocresol green, resazurin, neutral red, bromthymol blue, alpha-naphtholphthalein, o-cresolphthalein, phenolphthalein, and alizarin yellow G) almost completely inhibited the activities for ATP formation and ATP-Pi exchange at concentrations of 1 mM, and were studied in detail. 2. Of the eleven pH indicators, those other than alpha-naptholphthalein, o-cresolphthalein and phenolphthalein, when assayed at appropriate concentrations, inhibited ATP-Pi exchange, but not ATP hydrolysis. In ATP-Pi exchange, these eight pH indicators at the concentrations described above were competitive against Pi, and non-competitive against ATP. The remaining three kinds of pH indicators were non-competitive against either Pi or ATP, when assayed at concentrations of the dyes that inhibited both activities. 3. The amounts of pH indicators bound with chromatophores were measured. No correlation was found between the amounts of the bound dyes and the extents of their inhibition of either ATP formation or ATP-Pi exchange. 4. Ethyl orange (pKa=4.1) and 2, 4-dinitrophenol (pKa=3.9) stimulated ATP hydrolysis to the greatest extent. The latter dye was hardly bound with chromatophores. 5. The stimulatory effects of pH indicators on ATP hydrolysis were hardly affected by extraction of quinones from chromatophores. 6. Most of the pH indicators stimulated both succinate-cytochrome c2 and NADH-cytochrome c2 reductions in the dark. 7. The mechanism of uncoupling of the electron transfer system and the phosphorylation system by pH indicators and the mechanism of the coupling are discussed.

Adenosine Triphosphate↗

PubMed1977

Studies on the surface structure of the intracytoplasmic membrane in the photosynthetic purple bacterium Chromatium vinosum by means of chemical modification.

By means of a chemical modification technique, the surface structure of the intracytoplasmic membrane (chromatophores) of the photosynthetic bacterium Chromatium vinosum was investigated. Trinitrobenzenesulfonate was employed to modify the primary amino groups of phosphatidylethanolamine and proteins. The experimental results indicate that upon the chemical modification of intact cells, the amino groups on the inner surface of the chromatophores are trinitrophenylated, while upon the modification of isolated chromatophores, the amino groups of the outer surface are trinitrophenylated. Phosphatidylethanolamine is essentially equally distributed on the inner and outer surfaces of the chromatophores, while most proteins exist at the outer surface. In particular, a protein fraction, which is soluble in a mixture of chloroform/methanol, is located at the outer surface exposing a part of the amino groups in the aqueous phase.

Bacterial Chromatophores↗

PubMed1988

Diethylstilbestrol. Interactions with membranes and proteins and the different effects upon Ca2+- and Mg2+-dependent activities of the F1-ATPase from Rhodospirillum rubrum.

The hydrophobic compound diethylstilbestrol inhibits the generation of the proton gradient and the membrane potential in chromatophores from Rhodospirillum rubum and dissipates proton gradients over asolectin vesicle membranes. The Ca2+-ATPase activity of chromatophores, of purified F0F1-ATPase and of purified F1-ATPase is also decreased in the presence of diethylstilbestrol. Other repressed activities are the pyrophosphatase activity of soluble pyrophosphatase from yeast and the NADH oxidation by L-lactate:NAD oxidoreductase. We have previously reported that also ATP synthesis, PPi synthesis and PPi hydrolysis of R. rubrum chromatophores are inhibited by diethylstilbestrol [Strid et al. (1987) Biochim. Biophys. Acta 892, 236-244]. Addition of bovine serum albumin reverses or prevents diethylstilbestrol-induced inhibition of the activities tested. On the other hand, the Mg2+-ATPase activity of chromatophores, purified F0F1-ATPase and purified F1-ATPase are stimulated by low concentrations of diethylstilbestrol. On the basis of its hydrophobicity and the reversal of its inhibition by bovine serum albumin, diethylstilbestrol is proposed to act unspecifically on membranes and at hydrophobic domains of proteins. Such an attack upon the subunits of the F1-ATPase, altering the subunit interactions, is proposed to explain the different results obtained for the Ca2+-ATPase and the Mg2+-ATPase.

Adenosine Triphosphate↗

PubMed1992

Pigment cell refugia in homeotherms--the unique evolutionary position of the iris.

Homeotherms are generally considered to lack classical active dermal pigment cells (chromatophores) in their integument, attributable to the development of an outer covering coat of hair or feathers. However, bright colored dermal pigment cells, comparable to chromatophores of lower vertebrates, are found in the irides of many birds. We propose that, because of its exposed location, the iris is an area in which color from pigment cells has sustained a selective advantage and appears to have evolved independently of the general integument. In birds, the iris appears to have retained the potential for the complete expression of all dermal chromatophore types. Differences in cell morphology and the presence of unusual pigments in birds are suggested to be the result of evolutionary changes that followed the divergence of birds from reptiles. By comparison, mammals appear to have lost the potential for producing iridophores, xanthophores, or erythrophores comparable to those of lower vertebrates, even though some species possess brightly colored irides. It is proposed that at least one species of mammal (the domestic cat) has recruited a novel iridial reflecting pigment organelle originally developed in the choroidal tapetum lucidum. The potential presence of classical chromatophores in mammals remains open, as few species with bright irides have been examined.

Animals↗

PubMed1987

Transverse membrane topography of the B875 light-harvesting polypeptides of wild-type Rhodobacter sphaeroides.

Purified B875 light-harvesting complex, chromatophores, and spheroplast-derived vesicles from wild-type Rhodobacter sphaeroides were treated with proteinase K or trypsin, and the alpha and beta polypeptides were analyzed by electrophoretic, immunochemical, and protein-sequencing methods. With the purified complex, proteinase K digested both polypeptides and completely eliminated the A875 peak. Trypsin digested the alpha polypeptide and reduced the A875 by 50%. Proteinase K cleaved the beta polypeptide of chromatophores and the alpha polypeptide of spheroplast-derived vesicles. Sequence analyses of polypeptides extracted from proteinase K-treated chromatophores revealed that the beta polypeptide was cleaved between amino acids 4 and 5 from the N terminus. The N terminus of the alpha polypeptide was intact. We concluded that the N terminus of the beta polypeptide is exposed on the cytoplasmic membrane surface, and the difference in the digestion patterns between the spheroplast-derived vesicles and chromatophores suggested that the C terminus of the alpha polypeptide is exposed on the periplasmic surface.

Amino Acid Sequence↗