bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chlorophyll‐protein complexes of barley photosystem I
Authors: BASSI Roberto , SIMPSON David 
Published: March 2005

Photosystem I (PSI) preparations with a chlorophyll a/b ratio of 6.0 were isolated from barley thylakoids using two different methods. The high‐molecular‐mass complex (CP1a*) which is resolved by non‐denaturing gel electrophoresis had the same properties as a PSI preparation (PSI‐200) isolated by Triton X‐100 solubilisation of thylakoids followed by sucrose gradient ultracentrifugation. This material had a chlorophyll:P700 ratio of 208:1 and was composed of three different chlorophyll‐protein complexes which could be separated from each other by solubilising the PSI preparation in dodecyl maltoside followed by sucrose gradient ultracentrifugation. Approximately half of the chlorophyll, including all the chlorophyll b, was located in two antenna complexes designated LHCI‐680 and LHCI‐730, which were identified by their characteristic low‐temperature fluorescence emission spectra. The rest of the chlorophyll a was associated with the PSI reaction centre, P700 Chla‐P1, which fluoresced at 720 nm. Each chlorophyll‐protein complex had a unique polypeptide composition and characteristic circular dichroic and absorption spectra. The use of dodecyl maltoside instead of dodecyl sulphate resulted in a less denatured form of LHCI‐680, which fluoresced at 690 nm at 77 K. One of the sucrose gradient fractions contained a complex consisting of only LHCI‐730 and P700 Chla‐P1 which fluoresced at 731 nm, indicating that LHCI‐730 is structurally associated with P700 Chla‐P1 and quenches its fluorescence. Approximately threequarters of the light‐harvesting antenna chlorophyll was in LHCI‐730, but only about one‐quarter of the normal complement of LHCI‐730 was required to quench the reaction centre.By reducing the amount of Triton relative to the chlorophyll concentration, a PSI preparation (chlorophyll a/b ratio of 3.5) with a chlorophyll:P700 ratio of 300:1 was isolated. It contained no photosystem II, but a significant amount of LHCII which was functionally connected to the PSI reaction centre. Reconstitution studies demonstrated that excitation energy transfer from LHCII to PSI requires the presence of LHCI‐680, and we propose that, in PSI, the following linear excitation energy transfer sequence occurs: LHCII → LHCI‐680 → LHCI‐730 → P700 Chla‐P1.
Phenobarbital‐mediated modulation of gene expression in rat liver
Authors: LECHNER Maria Celeste , SINOGAS Carlos , OSÓRIO‐ALMEIDA Maria Leonor , FREIRE Maria Teresa , CHAUMET‐RIFFAUD Philippe , FRAIN Monique , SALA‐TREPAT José M. 
Published: March 2005

Phenobarbital evoques a pleiotypic response in the liver characterized by cell hypertrophy and mono‐oxygenase induction. These phenomena arise through complex modulation mechanisms changing the pattern of protein synthesis, distinct from those triggered by other well known inducers, like steroid hormones or polycyclic hydrocarbons.To investigate the mechanisms involved in regulating the expression of the phenobarbital‐inducible tissue‐specific genes, we constructed two libraries of recombinant bacterial plasmids pBR322 in Escherichia coli. Each library contains cDNA copies of polysomal poly(A)‐rich RNA obtained from control and 16‐h phenobarbital‐induced rat liver. A thousand cloned sequences from each library were screened by double‐cross colony hybridization using [32P]cDNA prepared from homologous and heterologous poly(A)‐rich RNAs as the probes. The statistical analysis of the results revealed that phenobarbital treatment significantly changes the relative abundance of different polysomal mRNA classes in rat liver.Clones corresponding to mRNAs clearly induced following phenobarbital treatment have been further selected by plasmid DNA dot hybridization, and used as probes for measuring the changes in each mRNA concentration in the whole cell and in the polysomal RNAs from rat livers, at different times after phenobarbital treatment.The fact that changes in the concentration of each specific mRNA in the polysomes does not parallel the variation of its total concentration in the cell indicates that the induced modulation of protein synthesis in the liver is brought about by mechanisms involving both transcriptional and translational regulation, since besides the increases in whole cellular mRNA concentration a marked mobilization of mRNA into active polysomes could be demonstrated during the onset of the adaptive response to phenobarbital.
Structural analysis of 5S rRNA, 5S rRNA‐protein complexes and ribosomes employing RNase H and d(GTTCGG)
Authors: LORENZ Siegfried , HARTMANN Roland K. , PIEL Norbert , ULBRICH Norbert , ERDMANN Volker A. 
Published: March 2005

The hybridization of d(GTTCGG) to eubacterial 5S rRNAs, 5S rRNA‐protein complexes, 70S ribosomes and 50S and 30S ribosomal subunits was investigated. This oligonucleotide, which may be considered to be an analogue of the TΨCG loop of tRNAs, was chosen in order to investigate a possible interaction between tRNAs with ribosomal components during protein synthesis. The hybridization was analysed by RNase H hydrolysis studies and, in the case of the ribosomes and ribosomal subunits, in addition with the radioactively labelled oligodeoxyribonucleotide in binding studies.The results obtained lead to the conclusion that nucleotides in loop c, i.e. positions 42–47, are available for oligonucleotide interaction in free Escherichia coli and Bacillus stearothermophilus 5S rRNAs and not available in the corresponding 5S rRNA‐protein complexes. The 70S ribosomes and ribosomal subunits did not interact with the oligonucleotide. Under the assumption that d(GTTCGG) is an analogue of the TΨCG loop of tRNAs and in view of the results obtained, we conclude that in the unprogrammed ribosomes the TΨCG loop of tRNAs does not interact via standard Watson‐Crick base pairs with the ribosomal 5S, 16S or 23S RNAs.
Further studies on the structure of the glycogen‐bound form of protein phosphatase‐1 from rabbit skeletal muscle
Authors: HIRAGA Akira , KEMP Bruce E. , COHEN Philip 
Published: March 2005

We have reported previously that the glycogen‐bound form of protein phosphatase‐1 (termed PP‐1G) is a heterodimer, composed of the 37‐kDa catalytic (C) subunit complexed to a 103‐kDa G‐subunit that anchors the enzyme to glycogen [Strålfors, P., Hiraga, A. and Cohen, P. (1985) Eur. J. Biochem. 149, 295–303]. An antibody raised against a synthetic peptide corresponding to the phosphorylation site on the G‐subunit was found to immunoprecipitate PP‐1G specifically. No precipitation occurred if the antibody was preincubated with the synthetic peptide, or if PP‐1G was replaced by either the isolated C‐subunit or protein phosphatase‐2A. The results confirm by a new and independent method that the G‐subunit is complexed to the C‐subunit, and that it is not a contaminant.The G‐subunit is remarkably sensitive to proteolysis. At the final stage of purification, PP‐1G was eluted as a broad peak of activity. The leading fractions contained the 37‐kDa C‐subunit and 103‐kDa G‐subunit, while the central and trailing fractions comprised the 37‐kDa C‐subunit plus a number of bands with molecular masses ranging over 40–80 kDa. The 40–80‐kDa bands were phosphorylated by cyclic‐AMP‐dependent protein kinase and tryptic digestion generated the identical phosphopeptides obtained by trypsinisation of the 103‐kDa G‐subunit. Furthermore, antibody to the G‐subunit immunoprecipitated protein phosphatase activity quantitatively in the leading, central and trailing fractions. The results demonstrate that the 40–80‐kDa polypeptides are fragments of the G‐subunit, and that fragments as small as 40 kDa retain the sites of phosphorylation as well as the ability to interact with the C‐subunit and with glycogen.Khatra [J. Biol. Chem. (1986) 261, 8944–8952] reported that the glycogen‐bound form of protein phosphatase‐1 did not contain a G‐subunit and that it was a dimer composed of two identical C‐subunits. The present work has shown that this proposal is incorrect, and that proteolysis of the G‐subunit to fragments that stain very poorly with Coomassie blue can explain why this error was made.
Murein biosynthesis in synchronized cells of Proteus mirabilis
Authors: GMEINER Jobst , SARNOW Elke 
Published: March 2005

Cells of Proteus mirabilis, synchronized by sucrose density gradient centrifugation, were grown in complex medium containing radioactive N‐acetylglucosamine. At various times, labelled murein sacculi were isolated and digested with endo‐N,O‐acetylmuramidase from Chalaropsis. The murein fragments thus obtained were separated into disaccharide peptides as the monomeric subunits and into peptide‐cross‐linked subunits by gel filtration. The subunits were further differentiated into O‐acetylated and non‐O‐acetylated species, and into subunits containing anhydro‐N‐acetylmuramic acid which were glycan chain terminators in the native sacculi. Quantification of the subunit species gave the following results.1. At specific times during the cell cycle, murein subunits were lost from the polymer and a transient decrease in cross‐linkage was observed.2. The overall degree of cross‐linkage in mature murein, i.e. the ratio of peptide‐cross‐linked subunits versus uncross‐linked subunits, was 1.15 as determined by regression analysis.3. Anhydro‐N‐acetylmuramic‐acid‐containing murein subunits representing glycan chain terminators were found either peptide‐cross‐linked or uncross‐linked as monomers. Since these two subunit species were recovered in a defined ratio of 1.6, mature murein consisted of at least two different types of glycan chains. On average, each chain contained 15.4 murein subunits.4. About 60% of the murein subunits in mature murein were O‐acetylated and showed a higher degree of cross‐linkage than the non‐O‐acetylated portion.Finally, following the composition of the sacculus during the cell cycle revealed a complex precursor‐product relationship between non‐O‐acetylated and O‐acetylated subunits during murein maturation. The data allowed us to deduce several features of the assembly process of murein sacculi.
Examination of the structural requirements for proliferation of peroxisomes and mitochondria in mouse liver by hypolipidemic agents, with special emphasis on structural analogues of 2‐ethylhexanoic acid
Authors: LUNDGREN Bo , MEIJER Johan , DePIERRE Joseph W. 
Published: March 2005

We have found here that there are clear structural requirements for peroxisome proliferation (monitored as increases in carnitine acetyltransferase activity, cyanide‐insensitive palmitoyl‐CoA oxidation, catalase and increases in the protein designated PPA 80) in mouse liver. From the investigation of ten structural analogues of 2‐ethylhexanoic acid, it could be concluded that the most effective proliferators all have an ethyl group as the substituent on carbon 2 of the main chain, which consists of six carbons. The further observation from this group of compounds that a charged group is required for effective proliferation leads us to speculate that such a group is involved in the molecular mechanism as well.Many, but not all, of the effective peroxisome proliferators in a second group of compounds contain a phenoxy group, often with a substituted α carbon. Interestingly, the 2,4‐dichlorophenoxyacetic and 2,4,5‐trichlorophenoxyacetic acids are both effective peroxisome proliferators, but the closely related p‐chlorophenoxyacetic acid is inactive in this respect, indicating that the chlorine atom at position 2 must be essential to the process in these cases.The results presented here also indicate that the structural requirements for proliferation of mitochondria are similar to those for proliferation of peroxisomes. Certainly, the most effective peroxisome proliferators also cause large increases in ‘mitochondrial’ protein and cytochrome oxidase activity, i.e. there is an obvious qualitative correlation.
Fate of injected 125I‐labeled cholera toxin taken up by rat liver in vivo
Authors: JANICOT Michel , DESBUQUOIS Bernard 
Published: March 2005

Subcellular fractionation techniques have been used to assess the localization of injected 125I‐labeled cholera toxin (125I‐CT) taken up by rat liver in vivo, and to determine whether internalization of the toxin is required for the generation of the active A1 peptide.The uptake of injected 125I‐CT into the liver is maximal at 5 min (about 10% injected dose/g). At this time the radioactivity is for the most part recovered in the microsomal (P) fraction, but later on it progressively associates with the mitochondrial‐lysosomal (ML) and supernatant fractions. The radioactivity is enriched 7‐fold in plasma membranes at 5–15 min, and 15–60‐fold in Golgi‐endosome (GE) fractions at 15–60 min.On analytical sucrose gradients the radioactivity associated with the P fraction is progressively displaced from the region of 5′‐nucleotidase (a plasma membrane marker) to that of galactosyltransferase (a Golgi marker). On Percoll gradients, however, it is displaced towards acid phosphatase (a lysosomal marker). Density‐shift experiments, using Triton WR 1339, suggest that some radioactivity associated with the P fraction (at 30 min) and all the radioactivity present in the ML fraction (at 2 h) is intrinsic to ácid‐phosphatase‐containing structures, presumably lysosomes. Comparable experiments using 3,3′‐diaminobenzidine cytochemistry indicate that the radioactivity present in GE fractions is separable from galactosyltransferase, and thus is presumably associated with endosomes.The fate of injected 125I‐labeled cholera toxin B subunit differs from that of the whole toxin by a more rapid uptake (and/or clearance) of the ligand into subcellular fractions, and a greater accumulation of ligand in the ML fraction.Analysis of GE fractions by SDS/polyacrylamide gel electrophoresis shows that, up to 10 min after injection of 125I‐CT, about 80% of the radioactivity is recovered as A subunit and 20% as B subunit, similarly to control toxin. Later on there is a time‐dependent decrease in the amount of A subunit and, at least with the intermediate GE fraction, a concomitant appearance of A1 peptide (about 15% of the total at 60 min). In contrast the radioactivity associated with plasma membranes remains indistinguishable from unused toxin.It is concluded that, upon interaction with hepatocytes, 125I‐CT (both subunits A and B) sequentially associates with plasma membranes, endosomes and lysosomes, and that endosomes may represent the major subcellular site at which the A1 peptide is generated.
Purification and characterization of a ribonuclease specific for poly(U) and poly(C) from the larvae of Ceratitis capitata
Authors: SIDERIS Diamantis C. , FRAGOULIS Emmanuel G. 
Published: March 2005

A specific ribonuclease was detected and purified to homogeneity from six‐day‐old larvae of the insect Ceratitis capitata and its homogeneity was checked by analysis in polyacrylamide gels in the presence of sodium dodecyl sulfate.The nuclease specifically degrades poly(U) and poly(C) whilst it fails to do so with other single‐stranded homopolyribonucleotides. The enzyme has a pH optimum in the region 7–9 and relative molecular mass of about 25000.The effect of this ribonuclease on the integrity of RNAs isolated from six‐day‐old larvae or rat liver was also studied.
Identification and sequencing of cDNA clones for the rodent negative acute‐phase protein α1‐inhibitor 3
Authors: SCHWEIZER Michael , TAKABAYASHI Kenji , GEIGER Thomas , LAUX Thomas , BIERMANN Gereon , BUHLER Jean‐Marie , GAUTHIER Francis , ROBERTS Lilian M. , HEINRICH Peter C. 
Published: March 2005

Rat α1‐inhibitor 3 clones were isolated by immunological screening of a λ gt11 cDNA library prepared from rat liver poly(A)‐rich RNA. The recombinant cDNA clones were identified by the absence of their immunoprecipitable products following hybrid‐arrested in vitro translation. The size of the cognate poly(A)‐rich RNA was estimated to be roughly 5000 residues. Approximately 16 h after induction of inflammation the amount of α1‐inhibitor 3 poly(A)‐rich RNA decreases as shown by dot‐blot hybridization and Northern analyses. The response of this negative acute‐phase plasma protein to inflammation may therefore be considered to be at the pretranslational level.The characterized DNA constitutes an open reading frame of 225 amino acids followed by a canonical eucaryotic polyadenylation signal and a poly(A) tail. Sequence microheterogeneity, particularly in the 3′‐flanking region was observed. An amino acid homology of 70% for α1‐inhibitor 3 with human and rodent α2‐macroglobulin emphasizes the evolutionary relationship of the macroglobulins.
The site of inhibition of the chloroplast electron‐transport system by 2,3‐dithiopropan‐1‐ol (BAL)
Authors: SHAHAK Yosepha , HIND Geoffrey , PADAN Etana 
Published: March 2005

BAL (2,3‐dithiopropan‐1‐ol) treatment of chloroplasts has previously been reported to induce a block in electron transport from water to NADP+ at a site preceding plastocyanin [Belkin et al. (1980) Biochim. Biophys. Acta 766, 563–569]. In the present work the block was further characterized. The following properties of BAL treatment are described.a) Inhibition of electron transport from water to lipophilic acceptors but not to silicomolybdate.b) Inhibition of the slow, sigmoidal phase of chlorophyll a fluorescence induction.c) Inability of N, N, N′,N′,‐tetramethyl‐p‐phenylenediamine to bypass the inhibition of NADP+ photoreduction with water as the electron donor.d) Inhibition of electron transport from externally added quinols to NADP+e) Inhibition of cytochrome f reduction by photosystem II, but not its oxidation by photosystem I.f) Inhibition of cytochrome b6 turnover and cytochrome f rereduction after single‐turnover flash illumination under cyclic electron‐flow conditions.The BAL‐induced block is therefore located between the secondary quinone acceptor (QB) and the cytochrome b6f complex. It was further found that (a) the isolated cytochrome complex is not inhibited after BAL treatment; (b) BAL‐reacted plastoquinone‐1 inhibits electron transport in chloroplasts; (c) BAL does not inhibit electron transport in chromatophores of Rhodospirilum rubrum or Rhodopseudomonas capsulata. It is suggested that the inhibition of electron transport in chloroplasts results from specific reaction of BAL with the endogenous plastoquinone.
Characteristics of the redox‐linked proton ejection in beef‐heart cytochrome c oxidase reconstituted in liposomes
Authors: PAPA Sergio , CAPITANIO Nazzareno , De NITTO Emanuele 
Published: March 2005

In this paper a study is presented of the characteristics of redox‐linked proton ejection exhibited by isolated beef‐heart cytochrome c oxidase incorporated in asolectin vesicles. The enzyme was 90% oriented ‘right‐side out’ as in the mitochondrial membrane. The effects on the H+/e− stoichiometry of the modalities of activation of electron flow, the pH of the medium and its ionic composition were investigated. The results obtained show that, whilst ferrocytochrome c pulses of the aerobic oxidase vesicles at neutral pH and in the presence of saturating concentrations of valinomycin and K+ to ensure charge compensation produced H+/e− ratios around 1 (as has been shown previously), oxygen pulses of reduced anaerobic vesicles supplemented with cytochrome c, gave H+/e− ratios around 0.3.The H+/e− ratios exhibited, with both reductant and oxidant pulses, a marked pH dependence. Maximum values were observed at pH 7.0–7.7, which decreased to negligible values at acidic pH with apparent pKa of 6.7–6.3.Mg2+ and Ca2+ caused a marked depression of the H+/e− ratio, which in the presence of these cations and after a few ferrocytochrome pulses, became negligible.Analysis of cytochrome c oxidation showed that the modalities of activation of electron flow and divalent cations exerted profound effects on the kinetics of cytochrome c oxidation by oxidase vesicles. The observations presented seem to provide interesting clues for the nature and mechanism of redox‐linked proton ejection in reconstituted cytochrome c oxidase.
Light‐dependent accumulation and localization of photosystem II proteins in maize
Authors: SUTTON Ann , SIEBURTH Leslie E. , BENNETT John 
Published: March 2005

We have raised antibodies against several major components of photosystem II. These antisera, which are directed against the apoproteins of two chlorophyll‐binding proteins (CPa‐1 and CPa‐2), the apoprotein of lightharvesting complex II and the 33‐kDa extrinsic protein of the oxygen‐evolving complex, were used to examine the light regulation of photosystem II assembly in maize. The principal findings of this study are as follows.1. The 33‐kDa protein is present in dark‐grown maize and the content increases 5–10‐fold upon illumination.2. The level of the protein is mediated at least in part by phytochrome and is independent of the accumulation of chlorophyll.3. In contrast, none of the three chlorophyll‐binding proteins examined was detectable in leaves of maize grown in darkness or under other light regimes where chlorophyll does not accumulate.4. Even in the absence of photosystem II assembly, the 33‐kDa protein is properly transported across the thylakoid into the lumen. However, the protein does not attach in the normal way to the inner surface of the membrane under these conditions.
Nitrogen catabolite regulation of proline permease in Saccharomyces cerevisiae
Authors: JAUNIAUX Jean‐Claude , VANDENBOL Micheline , VISSERS Stephan , BROMAN Kathleen , GRENSON Marcelle 
Published: March 2005

The proline permease gene PUT4 has been cloned. Nitrogen‐source regulation (‘ammonia sensitivity’) of this and at least two other amino‐acid permeases is believed to occur at two distinct levels, i.e. permease synthesis and permease activity. Therefore, PUT4 transcription/messenger stability was examined in the ammonia‐and proline‐grown wild type as well as in mutant strains supposedly affected at only one or at both of these levels. We report transcript‐level repression of proline permease synthesis in ammonia‐grown cells. Repression is lifted at this level in gdhCR, glnlts and gdhA mutants which exhibit pleiotropically derepressed permease and catabolic enzyme activities.On the other hand, the npil and npi2 mutations, formerly called mut2 and mut4, relieve an inactivation process which seems only to affect permeases. These mutations do not affect the detected PUT4 RNA level. The only known positive factor in proline permease regulation, the nitrogen permease reactivator protein Npr1, is believed to counteract the inactivation process on derepressing media. This protein appears to have an additional, indirect effect on PUT4 transcription/messenger stability: it would actually mediate repression via its activating effect on ammonia uptake.
The titre of juvenile hormone during the pupal and adult stages of the life cycle of Drosophila melanogaster
Authors: BOWNES Mary , REMBOLD Heinz 
Published: March 2005

Using combined gas chromatography/selected‐ion mass spectroscopy, the titer of juvenile hormone was determined for whole‐body extracts at various morphologically defined stages of the life cycle of Drosophila melanogaster. Only juvenile hormone III (JH‐III) was detected.JH‐III is present in early metamorphosis but by mid‐metamorphosis it is below the level of detection (0.05 pmol/g). It then increases as the pharate adult matures and rises dramatically, beginning just prior to eclosion and reaching 5–7 pmol/g shortly after eclosion. The titer then begins to fall again as the adults mature in both males and females, though the decrease is more rapid in females. Preliminary studies show that low levels of JH‐III are present during all the larval instars but are absent from eggs.