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E Mörschel

Publications and source records attributed to E Mörschel.

18 recordsLinked to original sources
PubMed2000

Ultrastructure of Acaryochloris marina, an oxyphotobacterium containing mainly chlorophyll d.

We present a detailed investigation of the ultrastructure of the chlorophyll a/d-containing unicellular oxyphotobacterium Acaryochloris marina, combining light and transmission electron microscopy and showing freeze fractures of this organism for the first time. The cells were 1.8-2.1 microm x 1.5-1.7 microm in size. The cell envelope consisted of a peptidoglycan layer of approximately 10 nm thickness combined with an outer membrane. Cell division was intermediate between the constrictive and the septum type. The nucleoplasm, which contained several carboxysomes, was surrounded by 7-11 concentrically arranged thylakoids, which were predominantly stacked, with the exception of distinct areas where phycobiliproteins were located. The thylakoids were perforated by channel-like structures connecting the central and peripheral portions of the cytoplasm and not yet observed in other organisms. In freeze fractures, the protoplasmic fracture faces of thylakoid membranes were densely covered with particles of inhomogenous size. The particle size histogram peaked at 10-11, 13 and 18 nm. The 18-nm particles are assumed to represent photosystem I trimers. The particles on exoplasmic fracture faces, proposed to represent photosystem II complexes, were significantly larger than the corresponding particles of cyanobacteria and clustered to form large aggregates. This kind of arrangement is unique among photosynthetic organisms.

Chlorophyll↗
PubMed1999

Molecular structure, localization and function of biliproteins in the chlorophyll a/d containing oxygenic photosynthetic prokaryote Acaryochloris marina.

We investigated the localization, structure and function of the biliproteins of the oxygenic photosynthetic prokaryote Acaryochloris marina, the sole organism known to date that contains chlorophyll d as the predominant photosynthetic pigment. The biliproteins were isolated by means of sucrose gradient centrifugation, ion exchange and gel filtration chromatography. Up to six biliprotein subunits in a molecular mass range of 15.5-18.4 kDa were found that cross-reacted with antibodies raised against phycocyanin or allophycocyanin from a red alga. N-Terminal sequences of the alpha- and beta-subunits of phycocyanin showed high homogeneity to those of cyanobacteria and red algae, but not to those of cryptomonads. As shown by electron microscopy, the native biliprotein aggregates are organized as rod-shaped structures and located on the cytoplasmic side of the thylakoid membranes predominantly in unstacked thylakoid regions. Biochemical and spectroscopic analysis revealed that they consist of four hexameric units, some of which are composed of phycocyanin alone, others of phycocyanin together with allophycocyanin. Spectroscopic analysis of isolated photosynthetic reaction center complexes demonstrated that the biliproteins are physically attached to the photosystem II complexes, transferring light energy to the photosystem II reaction center chlorophyll d with high efficiency.

Amino Acid Sequence↗
PubMed1997

Isolation and characterization of biliprotein aggregates from Acaryochloris marina, a Prochloron-like prokaryote containing mainly chlorophyll d.

Phycobiliprotein aggregates were isolated from the prokaryote Acaryochloris marina, containing chlorophyll d as major pigment. In the electron microscope the biliprotein aggregates appear as rod-shaped structures of 26.0 x 11.3 nm, composed of four ring-shaped subunits 5.8 nm thick and 11.7 nm in diameter. Spectral data indicate that the aggregates contain two types of biliproteins: phycocyanin and an allophycocyanin-type pigment, with very efficient energy transfer from the phycocyanin- to allophycocyanin-type constituent. The chromophore-binding polypeptides of the pigments have apparent molecular masses of 16.2 and 17.4 kDa. They crossreact with antibodies against phycocyanin and allophycocyanin from a red alga.

Bacterial Proteins↗
PubMed1997

Novel anaerobic ultramicrobacteria belonging to the Verrucomicrobiales lineage of bacterial descent isolated by dilution culture from anoxic rice paddy soil.

The use of dilution culture techniques to cultivate saccharolytic bacteria present in the anoxic soil of flooded rice microcosms allowed the isolation of three new strains of bacteria, typified by their small cell sizes, with culturable numbers estimated at between 1.2 x 10(5) and 7.3 x 10(5) cells per g of dry soil. The average cell volumes of all three strains were 0.03 to 0.04 microns3, and therefore they can be termed ultramicrobacteria or "dwarf cells." The small cell size is a stable characteristic, even when the organisms grow at high substrate concentrations, and thus is not a starvation response. All three strains have genomic DNA with a mol% G+C ratio of about 63, are gram negative, and are motile by means of a single flagellum. The three new isolates utilized only sugars and some sugar polymers as substrates for growth. The metabolism is strictly fermentative, but the new strains are oxygen tolerant. Sugars are metabolized to acetate, propionate, and succinate. Hydrogen production was not significant. In the presence of 0.2 atm of oxygen, the fermentation end products or ratios did not change. The phylogenetic analysis on the basis of 16S ribosomal DNA (rDNA) sequence comparisons indicates that the new isolates belong to a branch of the Verrucomicrobiales lineage and are closely related to a cloned 16S rDNA sequence (PAD7) recovered from rice paddy field soil from Japan. The isolation of these three strains belonging to the order Verrucomicrobiales from a model rice paddy system, in which rice was grown in soil from an Italian rice field, provides some information on the possible physiology and phenotype of the organism represented by the cloned 16S rDNA sequence PAD7. The new isolates also extend our knowledge on the phenotypic and phylogenetic depths of members of the order Verrucomicrobiales, to date acquired mainly from cloned 16S rDNA sequences from soils and other habitats.

Bacteria, Anaerobic↗
PubMed1993

Properties of the two isoenzymes of methyl-coenzyme M reductase in Methanobacterium thermoautotrophicum.

Methyl-coenzyme M reductase (MCR) catalyses the methane-forming step in the energy metabolism of methanogenic Archaea. It brings about the reduction of methyl-coenzyme M (CH3-S-CoM) by 7-mercaptoheptanoylthreonine phosphate (H-S-HTP). Methanobacterium thermoautotrophicum contains two isoenzymes of MCR, designated MCR I and MCR II, which are expressed differentially under different conditions of growth. These two isoenzymes have been separated, purified and their catalytic and spectroscopic properties determined. Initial-velocity measurements of the two-substrate reaction showed that the kinetic mechanism for both isoenzymes involved ternary-complex formation. Double reciprocal plots of initial rates versus the concentration of either one of the two substrates at different constant concentrations of the other substrate were linear and intersected on the abcissa to the left of the 1/v axis. The two purified isoenzymes differed in their Km values for H-S-HTP and for CH3-S-CoM and in Vmax. MCR I displayed a Km for H-S-HTP of 0.1-0.3 mM, a Km for CH3-S-CoM of 0.6-0.8 mM and a Vmax of about 6 mumol.min-1 x mg-1 (most active preparation). MCR II showed a Km for H-S-HTP of 0.4-0.6 mM, a Km for CH3-S-CoM of 1.3-1.5 mM and a Vmax of about 21 mumol.min-1 x mg-1 (most active preparation). The pH optimum of MCR I was 7.0-7.5 and that of MCR II 7.5-8.0. Both isoenzymes exhibited very similar temperature activity optima and EPR properties. The location of MCR I and of MCR II within the cell, determined via immunogold labeling, was found to be essentially identical. The possible basis for the existence of MCR isoenzymes in M. thermoautotrophicum is discussed.

Catalysis↗
PubMed1993

The unusual light-harvesting complex of Mantoniella squamata: supramolecular composition and assembly.

The supramolecular properties of the chlorophyll a/b/c light-harvesting protein complex of Mantoniella squamata were analyzed. The complex is built up of at least two subunits of M(r) 20,000 and 22,000, which are encoded in the nucleus as precursor proteins of M(r) 27,000. The chlorophyll a/b/c light-harvesting complex is the dominating protein of the thylakoids and is fractured with the protoplasmic membrane face as a 7.5 nm particle. These particles form paracrystalline arrays with a purported hexagonal arrangement in native thylakoids and form similar arrays when reconstituted in liposomes. The light-harvesting complexes are supposed to be trimers with a trigonal arrangement of the subunits. Preliminary amino acid sequence data show that the chlorophyll a/b/c light-harvesting complex of M. squamata is more related to the chlorophyll a/b complex of higher plants than to the light-harvesting complexes of chromophytan algae.

Amino Acid Sequence↗
PubMed1993

The atypical chlorophyll a/b/c light-harvesting complex of Mantoniella squamata: molecular cloning and sequence analysis.

cDNA species encoding precursor polypeptides of the chlorophyll a/b/c light-harvesting complex (LHC) of Mantoniella squamata were cloned and sequenced. The precursor polypeptides have molecular weights of 24.2 kDa and are related to the major chlorophyll a/b polypeptides of higher plants. Southern analysis showed that their genes belong to the nuclear encoded Lhc multigene family; the investigated genes most probably do not contain introns. The chlorophyll a/b/c polypeptides contain two highly conserved regions common to all LHC polypeptides and three hydrophobic alpha-helices, which span the thylakoid membrane. The first membrane-spanning helix, however, is not detected by predictive methods: its atypical hydrophilic domains may bind the chlorophyll c molecules within the hydrophobic membrane environment. Homology to LHC II of higher plants and green algae is specifically evident in the C-terminal region comprising helix III and the preceding stroma-exposed domain. The N-terminal region of 29 amino acids resembles the structure of a transit sequence, which shows only minor similarities to those of LHC II sequences. Strikingly, the mature light-harvesting polypeptides of M. squamata lack an N-terminal domain of 30 amino acids, which, in higher plants, contains the phosphorylation site of LHC II and simultaneously mediates membrane stacking. Therefore, the chlorophyll a/b/c polypeptides of M. squamata do not exhibit any light-dependent preference for photosystem I or II. The lack of this domain also indicates that the attractive forces between stacked thylakoids are weak.

Amino Acid Sequence↗
PubMed1993

Core substructure in phycobilisomes of red algae. II. The central part of the tricylindrical core--APCM--a constituent of hemidiscoidal phycobilisomes of Rhodella violacea.

The central part of the tricylindrical core of phycobilisomes from Rhodella violacea was isolated by hydroxylapatite adsorption chromatography followed by density gradient centrifugation. In the electron microscope negatively stained APCM complexes showed a tricylindrical face view with an edge length of 20 to 24 nm and a thickness of 9 to 10 nm in profile view. These complexes had a M(r) of 900,000, and a sedimentation coefficient 24S. The fluorescence emission maximum at room temperature lay at 671 nm when excited at 590 nm. The presence of the high molecular linker polypeptide LCM exclusively in APCM and the existence of beta AP19.5, alpha AP18, and beta AP17 were demonstrated in SDS-polyacrylamide gel electrophoresis. The presence of "trimeric" allophycocyanin complexes in a separate band, with a sedimentation coefficient 6S, confirms the uncoupling of these complexes from the core; their maximal fluorescence at 680 nm in the second derivative hints at alpha AP-8. The results indicate a high conformity in the molecular organization of the core of hemidiscoidal phycobilisomes of red algae (Rhodella violacea) and cyanobacteria (Mastigocladus laminosus).

Bacterial Proteins↗
PubMed1987

Purification and characterization of an 8-hydroxy-5-deazaflavin-reducing hydrogenase from the archaebacterium Methanococcus voltae.

A methylviologen and 8-hydroxy-5-deazaflavin(F420)-reducing hydrogenase was purified over 800-fold to near homogeneity from the archaebacterium Methanococcus voltae with 10 U mg-1 F420-reducing activity. It is the only hydrogenase in this organism. The enzyme showed Km values of 16 microM for F420 and 1.2 mM for methylviologen. A turnover number of 1050 min-1 was calculated for the minimal active unit. The protein tends to aggregate. The molecular mass of the minimal active unit is 105 kDa. Larger molecules of 745 kDa were regularly observed. The enzyme was resolved into subunits with molecular masses of 55 kDa, 45 kDa, 37 kDa and 27 kDa by SDS/polyacrylamide gel electrophoresis. Reversible conversion of an anionic into an uncharged form was observed by DEAE-cellulose chromatography with concomitant changes in substrate specificities. The methylviologen-reducing activity was heat-resistant up to 65 degrees C and was not affected by antiserum raised against the native enzyme, while F420 reduction was inactivated by both treatments. Nickel and selenium contents were determined as 0.6-0.7 mol each, FAD content as 1 mol and iron as 4.5 mol/mol protein (105 kDa), respectively. Electron micrographs taken from the purified enzyme show ring-shaped molecules of 18 nm diameter, which represent the high-molecular-mass species of the enzyme.

Archaea↗
PubMed1986

Methanogenesis and ATP synthesis in a protoplast system of Methanobacterium thermoautotrophicum.

When Methanobacterium thermoautotrophicum cells were incubated in 50 mM potassium phosphate buffer (pH 7.0) containing 1 M sucrose and autolysate from Methanobacterium wolfei, they were transformed into protoplasts. The protoplasts, which possessed no cell wall, lysed in buffer without sucrose. Unlike whole cells, the protoplasts did not show convoluted internal membrane structures. The protoplasts produced methane from H2-CO2 (approximately 1 mumol min-1 mg of protein-1) at about 50% the rate obtained for whole cells, and methanogenesis was coupled with ATP synthesis. Addition of the protonophore 3,5-di-tert-butyl-4-hydroxybenzylidenemalononitrile (SF-6847) to protoplast suspensions resulted in a dissipation of the membrane potential (delta psi), and this was accompanied by a parallel decrease in the rates of ATP synthesis and methanogenesis. In this respect protoplasts differed from whole cells in which ATP synthesis and methanogenesis were virtually unaffected by the addition of the protonophore. It is concluded that the insensitivity of whole cells to protonophores could be due to internal membrane structures. Membrane preparations produced from lysis of protoplasts or by sonication of whole cells gave comparatively low rates of methanogenesis (methylcoenzyme M methylreductase activity, less than or equal to 100 nmol of CH4 min-1 mg of protein-1), and no coupling with ATP synthesis could be demonstrated.

Adenosine Triphosphate↗
PubMed1985

Phosphorylation and phosphate-ATP exchange catalyzed by the ATP synthase isolated from Wolinella succinogenes.

The ATP synthase, isolated from Wolinella (formerly Vibrio) succinogenes could be fully incorporated into liposomes without significant cleavage of the enzyme or loss of activity. These proteoliposomes, but not the isolated enzyme, catalyzed phosphate-ATP exchange and the phosphorylation of ADP which was driven by an artificially imposed delta mu H across the liposomal membrane. Phosphorylation driven by light was catalyzed by proteoliposomes containing also bacteriorhodopsin. The three activities were similarly sensitive to protonophores or dicyclohexylcarbodiimide. This sensitivity was similar to that of the electron-transport-driven phosphorylation catalyzed by bacterial membrane vesicles. With a delta mu H value 280 mV to drive phosphorylation the turnover number of the enzyme was in the same order of magnitude as that measured in the electron-transport-driven phosphorylation catalyzed by the bacterial membrane. When the delta mu H was below 150 mV, the phosphorylation activity of the incorporated enzyme was two orders of magnitude slower, and was about as fast as light-driven phosphorylation or as the exchange reaction.

Adenosine Triphosphate↗
PubMed1983

Structural properties of the proteoliposomes catalyzing electron transport from formate to fumarate.

The electron-transport chain catalyzing fumarate reduction by formate has recently been reconstituted from the formate dehydrogenase complex and the fumarate reductase complex from Vibrio succinogenes, in a liposomal preparation containing vitamin K-1 (Unden, G. and Kröger, A. (1982) Biochim. Biophys. Acta 682, 258-263). We have now investigated the structural properties of this preparation. The preparation was found to consist of a homogeneous population of unilamellar proteoliposomes with an average diameter of about 100 nm and an internal volume of 2-4 ml/g phospholipid. The buoyant density (1.07 g/ml) was consistent with the protein/phospholipid ratio (0.2 g/g) of the preparation. Leakage of glucose from the internal spaces of the proteoliposomes was negligibly slow. Proteoliposomes prepared with either of the enzyme complexes showed peripheral projections mainly on the outer surface, when examined by electron microscopy after negative staining. The size, orientation and surface density of the projections were consistent with those of the enzymes. Most of the substrate and dye-reactive sites (70-90%) of the enzymes in the proteoliposomes were accessible to external non-permeant substrates. The proteoliposomes catalyzing electron transport were formed by freeze-thawing a mixture of liposomes and protein-phospholipid complexes which did not perform electron transport from formate to fumarate. Nearly the entire amount of the enzymes supplied (0.2 g protein/g phospholipid) was incorporated into the liposomes by this procedure. The transformation of liposomes into proteoliposomes was accompanied by exchange of the internal solutes with the external medium.

Aldehyde Oxidoreductases↗
PubMed1983

Reconstitution of cytochrome f/b6 and CF0-CF1 ATP synthetase complexes into phospholipid and galactolipid liposomes.

Cytochrome f/b6 and ATP synthetase (CF0-CF1) complexes from spinach chloroplasts have been reconstituted into liposomes prepared from soybean phospholipids and purified spinach galactolipids. Freeze-fracture analysis revealed homogeneous populations of particles spanning the lipid bilayers with their elongated axes perpendicular to the membrane plane. The lipid composition of the liposomes had no effect on the size of the reconstituted complexes, the average diameter of cytochrome f/b6 complex measuring 8.5 nm, and of the CF0 base piece of the ATP synthetase, 9.5 nm. When reconstituted cytochrome f/b6 complexes were cross-linked by means of antibodies prepared against the whole complex, the thus aggregated particles formed either hexagonal or square arrays. In both instances the center-to-center spacing of the particles was 8.3 nm, thereby suggesting that this value could be closer to the real diameter of the complexes than the one obtained from measuring individual particles. Assuming an ellipsoidal shape for these particles, and using a measured height of 11 nm, a molecular weight of approximately 280,000 could be calculated for the reconstituted cytochrome f/b6 complex, consistent with a dimeric configuration. In many instances the crystalline sheets of antibody-aggregated cytochrome f/b6 complexes were found to be free in the buffer solution; apparently the antibody-induced strains caused the sheet-like aggregates to pop out of the liposomal membranes. Agglutination studies of inside-out and right-side-out thylakoid vesicles revealed the antigenic determinants of the cytochrome f and cytochrome b6 polypeptides to be exposed on the inner thylakoid surface and to be present in stacked and unstacked membrane regions. The molecular weight calculated from the size of freeze-fractured CF0 base pieces was over twice the value determined by x-ray scattering data. This discrepancy may be caused by significant lipid domains within the base piece, or by an unusual fracturing behavior of the base piece in reconstituted liposomes.

Adenosine Triphosphatases↗
PubMed1980

Biliprotein assembly in the disc-shaped phycobilisomes of Rhodella violacea. Electron microscopical and biochemical analysis of B-phycoerythrin and B-phycoerythrin--C-phycocyanin aggregates.

Hexameric B-phycoerythrin (alpha beta)6 gamma is a double disc of about 10.7 x 4.3 nm; each single disc consists of a six membered periphery (alpha beta)3, the subunits of which are assumed to be associated in alternating positions with little or no staggering. A central subunit, almost certainly the gamma-subunit, penetrates both rings linking them tightly together. Hexameric C-phycocyanin (alpha beta)6 has the same construction but lacks this central subunit. In urea gel electrophoresis B-phycoerythrin I and II separate into three bands alpha, beta, and gamma in a relative molar ratio of 6:6:1. The molecular weights of the alpha-, beta-, gamma-subunits, estimated from SDS gels were 18 700, 18 700 and 29 200 and 18 300, 18 300 and 29 900 for B-phycoerythrin I and II, respectively, resulting in molecular weights of 253 600 and 249 500 for both hexameric aggregates. In density gradient centrifugation a sedimentation coefficient s20,w . 10(13) of 11.3 and a molecular weight of 244 000 were calculated. In sedimentation analyses of partially dissociated phycobilisomes a fragment consisting of two phycoerythrin hexamers with a sedimentation constant of 18 S (dodecamer) and tripartite units with two B-phycoerythrin hexamers associated with one polar C-phycocyanin hexamer with a sedimentation constant of 22 S were demonstrated. The corresponding molecular weight of the tripartite units, about 800 000, coincides well with morphological measurements on the basis of an average protein packing density and with earlier estimates on cross-linked biliprotein aggregates in gradient gel electrophoresis. The spaces of 1.2 to 3.0 nm between the hexamers give rise to a strong 6.0 nm periodicity within the tripartite units, the weak 3.0 nm periodicity originates from the double-rings of the constituent hexamers.

Centrifugation, Density Gradient↗
PubMed1978

Biliprotein assemble in the disc-shaped phycobilisomes of Rhodella violacea. On the molecular composition of energy-transfering complexes (tripartite units) forming the periphery of the phycobilisome.

Heterogeneous complexes with a molecular weight of about 790000 containing B-phycoerythrin (Bangiales phycoerythrin) and C-phycocyanin (Cyanophyceae phycocyanin) in a molar pigment ratio of 2:1 were isolated from purified, dissociated phycobilisomes. Electron microscopical investigations revealed structures of three discs aggregated face to face with an apparent distance of 1.5 nm between each disc. Two discs may represent phycoerythrin and one phycocyanin. The complexes are structurally identical with tripartite units of the phycobilisome periphery. Fluorescence data confirmed the integrity of isolated tripartite units. Excitation at 546 nm gives a fluorescence maximum at 644 nm, indicating intermolecular transfer of excitation energy from phycoerythrin to phycocyanin. Comparative subunit analyses and spectral data suggested that no allophycocyanin is present. Cross-linking experiments gave evidence for a polar arrangement of phycocyanin within the complex. This pigment itself is an aggregate of two smaller molecules each having a molecular weight of about 140000. Tripartite units contain all the phycoerythrin and phycocyanin of the phycobilisome. On this basis, a phycobilisome model is proposed which combines the aspects of biliprotein distribution, energy transfer and fine structure.

Macromolecular Substances↗
PubMed1975

Cryptomonad biliprotein: phycocyanin-645 from a Chroomonas species.

The properties of phycocyanin-645 from the fresh water cryptomonad Chroomonas spec. were investigated after the pigment was isolated and purified by a combination of differential ammonium sulphate fractionation, gel filtration chromatography and ammonium sulphate gradient elution. Phycocyanin-645 is characterized by absorption maxima at 645 nm, 584 nm, 369 nm, 275 nm and shoulders at 340 nm and 620 nm. The CD spectrum has a negative maximum at 645 nm and a positive maximum at 584 nm with a shoulder at 610 nm. The fluorescence emission spectrum is asymmetrical and shows a maximum at 660 nm and a shoulder at approximately 715 nm. The molecular weight of the native phycocyanin-645, estimated by gel filtration, is 45000 for all multiple pigment forms below. Phycocyanin-645 is heterogeneous as revealed by isoelectric focusing with pIs at 7.03, 6.17, 5.75, 5.25 and 4.88, respectively, the main bands lying at pI 7.03 and pI 6.17. This was confirmed by polyacrylamide gel electrophoresis; five pigment compoents differing in mobility were found. We propose the term "multiple pigment forms" for these five phycocyanin-645 modifications. Calibrated SDS gel electrophoresis shows phycocyanin-645 to consist of three subunits, two light chains (alpha1, alpha2), having molecular weights of 9200 and 10400, respectively, and one heavy chain (beta), having a molecular weight of 15 500. Suggesting a 1:1:2 ratio between the subunits, the quaternary structure of the pigment molecule is alpha1beta--alpha2beta1.

Eukaryota↗