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Structural Prerequisites (structural + prerequisite)
Selected AbstractsFunctional Morphology of the Nasal Complex in the Harbor Porpoise (Phocoena phocoena L.)THE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 6 2009Stefan Huggenberger Abstract Toothed whales (Odontoceti, Cetacea) are the only aquatic mammals known to echolocate, and probably all of them are able to produce click sounds and to synthesize their echoes into a three-dimensional "acoustic image" of their environment. In contrast to other mammals, toothed whales generate their vocalizations (i.e., echolocation clicks) by a pneumatically-driven process in their nasal complex. This study is dedicated to a better understanding of sound generation and emission in toothed whales based on morphological documentation and bioacoustic interpretation. We present an extensive description of the nasal morphology including the nasal muscles in the harbor porpoise (Phocoena phocoena) using macroscopical dissections, computer-assisted tomography, magnetic resonance imaging, and histological sections. In general, the morphological data presented here substantiate and extend the unified "phonic lips" hypothesis of sound generation in toothed whales suggested by Cranford et al. (J Morphol 1996;228:223,285). There are, however, some morphological peculiarities in the porpoise nasal complex which might help explain the typical polycyclic structure of the clicks emitted. We hypothesize that the tough connective tissue capsule (porpoise capsule) surrounding the sound generating apparatus is a structural prerequisite for the production of these high-frequency clicks. The topography of the deep rostral nasal air sacs (anterior nasofrontal and premaxillary sacs), narrowing the potential acoustic pathway from the phonic lips to the melon (a large fat body in front of the nasal passage), and the surrounding musculature should be crucial factors in the formation of focused narrow-banded sound beams in the harbor porpoise. Anat Rec, 292:902,920, 2009. © 2009 Wiley-Liss, Inc. [source] Proximate, "Parallel-In-Plane" Preoriented Bis(diazenes) , In-Plane Delocalized Bis(homoconjugated) 4N/5(6)e AnionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 21 2003Eberhard Beckmann Abstract Synthetic details are presented for a series of more or less rigid, "parallel-in-plane" preoriented bis(diazenes), with N=N/N=N distances (d) of 3.3,2.9 Å and interorbital angles (,) of 142,164° (X-ray crystal structures). DFT calculations (B3LYP/6,31G*) and one-/two-electron reduction experiments with the two least preoriented, most "distant" bis(diazenes) (dN=N/N=N ca. 3.3 Å; , 142,146°) provide more insight into the structural prerequisites for bis(homoconjugative) in-plane electron delocalization in 4N/5e radical anions and 4N/6e dianions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Molecular mechanism of DNA replication-coupled inactivation of the initiator protein in Escherichia coli: interaction of DnaA with the sliding clamp-loaded DNA and the sliding clamp-Hda complexGENES TO CELLS, Issue 6 2004Masayuki Su'etsugu In Escherichia coli, the ATP-DnaA protein initiates chromosomal replication. After the DNA polymerase III holoenzyme is loaded on to DNA, DnaA-bound ATP is hydrolysed in a manner depending on Hda protein and the DNA-loaded form of the DNA polymerase III sliding clamp subunit, which yields ADP-DnaA, an inactivated form for initiation. This regulatory DnaA-inactivation represses extra initiation events. In this study, in vitro replication intermediates and structured DNA mimicking replicational intermediates were first used to identify structural prerequisites in the process of DnaA-ATP hydrolysis. Unlike duplex DNA loaded with sliding clamps, primer RNA-DNA heteroduplexes loaded with clamps were not associated with DnaA-ATP hydrolysis, and duplex DNA provided in trans did not rescue this defect. At least 40-bp duplex DNA is competent for the DnaA-ATP hydrolysis when a single clamp was loaded. The DnaA-ATP hydrolysis was inhibited when ATP-DnaA was tightly bound to a DnaA box-bearing oligonucleotide. These results imply that the DnaA-ATP hydrolysis involves the direct interaction of ATP-DnaA with duplex DNA flanking the sliding clamp. Furthermore, Hda protein formed a stable complex with the sliding clamp. Based on these, we suggest a mechanical basis in the DnaA-inactivation that ATP-DnaA interacts with the Hda-clamp complex with the aid of DNA binding. [source] Structural properties of orexins for activation of their receptorsJOURNAL OF PEPTIDE SCIENCE, Issue 4 2006Manja Lang Abstract The closely related neuropeptides orexin A and orexin B mediate their actions, including the regulation of sleep and appetite, by the activation of the orexin 1 and 2 receptors. To elucidate the structural prerequisites for receptor activation and subtype selectivity, we performed multiple amino acid substitutions within the sequence of orexin A and human orexin B-(6-28)-peptide and analyzed their solution structures by CD spectroscopy and their activity at both receptors in Ca2+ mobilization assays. For orexin A, we showed that the basic amino acids within the segment of residues 6,14 were important for the activation of both receptors. Furthermore, we showed that the restriction via disulfide bonds is not required to maintain the active structure of orexin A. The kink region of h orexin B has been shown to be important for Ox2R selectivity, which is not mediated by the restriction of the turn structure. Additionally, we showed that no particular secondary structure is required for receptor subtype selectivity. Copyright © 2005 European Peptide Society and John Wiley & Sons, Ltd. [source] | |||||||||||||