kirjoittanut Hans von Berlepsch ; suomentanut ja suomalaisiin oloihin sovitellut A. J. Mela

Ilmestynyt aikaisemmin saksan, englannin, ranskan, italian ja ruotsin kielillä. Varustettu 8 väritaululla ja 17 tekstikuvall

Charakterisierung der vektoriellen Acylierung als Mechanismus des Fettsäuretransports in Synechocystis sp. PCC 6803

Transfer of fatty acids across biological membranes is a largely uncharacterized process. In unicellular organisms, like Escherichia coli or Saccharomyces cerevisiae vectorial acylation by acyl-activating enzymes is discussed as mechanism for fatty acid transport. In the present work, studies on the only acyl-acyl-carrier protein synthetase SynAas of Synechocystis sp. PCC 6803 with regard to fatty acid transport were performed. Cells deficient in SynAas were highly resistant to externally provided α-linolenic acid. Upon treatment with external α-linolenic acid the wild type showed continuous accumulation of α-linolenic acid in cellular lipids and as free fatty acid in the cell. Long-term incubation with α-linolenic acid for 10 hours led to structural changes in the integrity of thylakoid membranes and a dramatic increase in electron transport rate (ETR) in wild type cells. After 24 hours of incubation the accumulation resulted in bleaching and dying of the wild type cells, whereas the loss of function mutant ∆synaas was completely unaffected by this treatment. Furthermore, Saccharomyces cerevisiae wild type cells displayed sensitivity against α-linolenic acid, whereas the “loss of function” mutant in the fatty acid importer FAT1p showed resistance upon α-linolenic acid incubation. Heterologous expression of SynAas in yeast wild type and ∆fat1 mutant cells resulted in an increased sensitivity against exogenous α-linolenic acid, which implies elevated levels of uptake of toxic α-linolenic acid through SynAas. In addition, liposome assays provided direct evidence for the ability of purified SynAas protein to mediate [14C]-α-linolenic acid retrieval from preloaded liposome membranes. Taken together, the data show that the acyl-activating enzyme SynAas is necessary and sufficient to mediate transfer of fatty acids across a biological membrane. These facts were used to derive a model for α-linolenic acid uptake and metabolism in Synechocystis. In addition, the ABC- Transporter SynAbc could be identified as putative fatty acid exporter. The SynAbc “loss-of-function” mutant ∆synabc exhibited increased sensitivity upon α-linolenic acid treatment and massive accumulation of exogenously applied fatty acid, compared to wild type. The ∆synaas mutant secreted free fatty acids into the media. A simultaneous defect in the SynAbc gene completely prevented accumulation of fatty acids in the media, which gives rise to the assumption that SynAbc facilitates fatty acid export in Synechocystis

Stereochemistry‐Controlled Supramolecular Architectures of New Tetrahydroxy‐Functionalised Amphiphilic Carbocyanine Dyes

The syntheses of novel amphiphilic 5,5′,6,6‐tetrachlorobenzimidacarbocyanine (TBC) dye derivatives with aminopropanediol head groups, which only differ in stereochemistry (chiral enantiomers, meso form and conformer), are reported. For the achiral meso form, a new synthetic route towards asymmetric cyanine dyes was established. All compounds form J aggregates in water, the optical properties of which were characterised by means of spectroscopic methods. The supramolecular structure of the aggregates is investigated by means of cryo‐transmission electron microscopy, cryo‐electron tomography and AFM, revealing extended sheet‐like aggregates for chiral enantiomers and nanotubes for the mesomer, respectively, whereas the conformer forms predominately needle‐like crystals. The experiments demonstrate that the aggregation behaviour of compounds can be controlled solely by head group stereochemistry, which in the case of enantiomers enables the formation of extended hydrogen‐bond chains by the hydroxyl functionalities. In case of the achiral meso form, however, such chains turned out to be sterically excluded

Inhibition of peptide aggregation by means of enzymatic phosphorylation

As is the case in numerous natural processes, enzymatic phosphorylation can be used in the laboratory to influence the conformational populations of proteins. In nature, this information is used for signal transduction or energy transfer, but has also been shown to play an important role in many diseases like tauopathies or diabetes. With the goal of determining the effect of phosphorylation on amyloid fibril formation, we designed a model peptide which combines structural characteristics of α-helical coiled-coils and β-sheets in one sequence. This peptide undergoes a conformational transition from soluble structures into insoluble amyloid fibrils over time and under physiological conditions and contains a recognition motif for PKA (cAMP- dependent protein kinase) that enables enzymatic phosphorylation. We have analyzed the pathway of amyloid formation and the influence of enzymatic phosphorylation on the different states along the conformational transition from random-coil to β-sheet-rich oligomers to protofilaments and on to insoluble amyloid fibrils, and we found a remarkable directing effect from β -sheet-rich structures to unfolded structures in the initial growth phase, in which small oligomers and protofilaments prevail if the peptide is phosphorylated

Vibronic origin of long-lived coherence in an artificial molecular light harvester

Natural and artificial light harvesting processes have recently gained new interest. Signatures of long lasting coherence in spectroscopic signals of biological systems have been repeatedly observed, albeit their origin is a matter of ongoing debate, as it is unclear how the loss of coherence due to interaction with the noisy environments in such systems is averted. Here we report experimental and theoretical verification of coherent exciton-vibrational (vibronic) coupling as the origin of long-lasting coherence in an artificial light harvester, a molecular J-aggregate. In this macroscopically aligned tubular system, polarization controlled 2D spectroscopy delivers an uncongested and specific optical response as an ideal foundation for an in-depth theoretical description. We derive analytical expressions that show under which general conditions vibronic coupling leads to prolonged excited-state coherence

Com o diabo no corpo: os terríveis papagaios do Brasil colônia

Desde a Antiguidade, papagaios, periquitos e afins (Psittacidae) fascinaram os europeus por seu vivo colorido e uma notável capacidade de interação com seres humanos. A descoberta do Novo Mundo nada faria além de acrescentar novos elementos ao tráfico de animais exóticos há muito estabelecido pelos europeus com a África e o Oriente. Sem possuir grandes mamíferos, a América tropical participaria desse comércio com o que tinha de mais atrativo, essencialmente felinos, primatas e aves - em particular os papagaios, os quais eram embarcados em bom número. Contudo, a julgar pelos documentos do Brasil colônia, esses voláteis podiam inspirar muito pouca simpatia, pois nenhum outro animal - exceto as formigas - foi tantas vezes mencionado como praga para a agricultura. Além disso, alguns psitácidas mostravam-se tão loquazes que inspiravam a séria desconfiança de serem animais demoníacos ou possessos, pois só três classes de entidades - anjos, homens e demônios - possuíam o dom da palavra. Nos dias de hoje, vários representantes dos Psittacidae ainda constituem uma ameaça para a agricultura, enquanto os indivíduos muito faladores continuam despertando a suspeita de estarem possuídos pelo demônio. Transcendendo a mera curiosidade, essa crença exemplifica o quão intrincadas podem ser as relações do homem com o chamado “mundo natural”, revelando um universo mais amplo e multifacetado do que se poderia supor a princípio. Nesse sentido, a existência de aves capazes de falar torna essa relação ainda mais complexa e evidencia que as dificuldades de estabelecer o limite entre o animal e o humano se estendem além dos primatas e envolvem as mais inusitadas espécies zoológicas.Since ancient times, parrots and their allies (Psittacidae) have fascinated Europeans by their striking colors and notable ability to interact with human beings. The discovery of the New World added new species to the international exotic animal trade, which for many centuries had brought beasts to Europe from Africa and the Orient. Lacking large mammals, tropical America participated in this trade with its most appealing species, essentially felines, primates and birds - especially parrots - which were shipped in large numbers. It should be noted, however, that at times these birds were not well liked. In fact, according to documents from colonial Brazil, only the ants rank higher than parrots as the animals most often mentioned as agricultural pests. On the other hand, some of these birds were so chatty that people suspected them to be demonic or possessed animals, since only three classes of beings - angels, men and demons - have the ability to speak. Nowadays, several Psittacidae still constitute a threat to agriculture, and the suspicion that extremely talkative birds were demon possessed has also survived. More than a joke or a mere curiosity, this belief exemplifies how intricate man’s relationships with the “natural world” may be. In this sense, the existence of birds that are able to speak adds a further twist to these relationships, demonstrating that the problem of establishing a boundary between the animal and the human does not only involve primates, but also includes some unusual zoological species

Mitteilungen \ufcber neue und seltene s\ufcdamerikanische V\uf6gel

Start Page: 548End Page: 55