Mysterious bio-duck sound attributed to the Antarctic minke whale (Balaenoptera bonaerensis)

For decades, the bio-duck sound has been recorded in the Southern Ocean, but the animal producing it has remained a mystery. Heard mainly during austral winter in the Southern Ocean, this ubiquitous sound has been recorded in Antarctic waters and contemporaneously off the Australian west coast. Here, we present conclusive evidence that the bio-duck sound is produced by Antarctic minke whales (Balaenoptera bonaerensis). We analysed data from multi-sensor acoustic recording tags that included intense bio-duck sounds as well as singular downsweeps that have previously been attributed to this species. This finding allows the interpretation of a wealth of long-term acoustic recordings for this previously acoustically concealed species, which will improve our understanding of the distribution, abundance and behaviour of Antarctic minke whales. This is critical information for a species that inhabits a difficult to access sea-ice environment that is changing rapidly in some regions and has been the subject of contentious lethal sampling efforts and ongoing international legal action.     

Removal of the 9-methyl group of retinal inhibits signal transduction in the visual process. A Fourier transform infrared and biochemical investigation

The photoreaction of opsin regenerated with 9-demethylretinal has been investigated by UV-vis spectroscopy, flash photolysis experiments, and Fourier transform infrared difference spectroscopy. In addition, the capability of the illuminated pigment to activate the retinal G-protein has been tested. The photoproduct, which can be stabilized at 77 K, resembles more the lumirhodopsin species, and only minor further changes occur upon warming the sample to 170 K (stabilizing lumirhodopsin). UV-vis spectroscopy reveals no further changes at 240 K (stabilizing metarhodopsin I), but infrared difference spectroscopy shows that the protein as well as the chromophore undergoes further molecular changes which are, however, different from those observed for unmodified metarhodopsin I. UV-vis spectroscopy, flash photolysis experiments, and infrared difference spectroscopy demonstrate that an intermediate different from metarhodopsin II is produced at room temperature, of which the Schiff base is still protonated. The illuminated pigment was able to activate G-protein, as assayed by monitoring the exchange of GDP for GTP gamma S in purified G-protein, only to a very limited extent (approximately 8% as compared to rhodopsin). The results are interpreted in terms of a specific steric interaction of the 9-methyl group of the retinal in rhodopsin with the protein, which is required to initiate the molecular changes necessary for G-protein activation. The residual activation suggests a conformer of the photolyzed pigment which mimics metarhodopsin II to a very limited extent.     

Investigations of the rhodopsin/Meta I and rhodopsin/Meta II transitions of bovine rod outer segments by means of kinetic infrared spectroscopy

We have applied our recently developed technique of flash induced kinetic infrared spectroscopy to the rhodopsin/Meta I and rhodopsin/Meta II transitions. Features of the infrared spectrum reflecting the C=C-vibration and the isomeric form of the chromophore are in agreement with resonant Raman experiments. Different results are obtained for the C=N-vibration of the Schiff base retinal opsin link. They are interpreted in terms of a Schiff base protonated via an hydrogen bond. A proton transfer in the excited state is suggested to explain the deviating results. In addition we have obtained spectral changes which cannot be attributed to molecular changes in the chromophore. We assume that these spectral features reflect molecular events in the protein part of rhodopsin.     

Asp85 is the only internal aspartic acid that gets protonated in the M intermediate and the purple-to-blue transition of bacteriorhodopsin. A solid-state 13C CP-MAS NMR investigation.

High-resolution solid-state 13C NMR spectra of the ground state and M intermediate of the bacteriorhodopsin mutant D96N with the isotope label at [4-13C]Asp and [11-13C]Trp were recorded. The NMR spectra show that Asp85 is protonated in the M intermediate. The environment of Asp85 is quite hydrophobic. On the other hand, Asp212 remains deprotonated and a slight shift to lower field indicates a more hydrophilic environment. Asp85 also protonates in the purple-to-blue transition of bacteriorhodopsin in the deionized membrane, where it experiences a similar environment to M. The shift of Trp resonances in M reflect a conformational change of the protein in forming the M intermediate.     

Structural investigation of bacteriorhodopsin and some of its photoproducts by polarized Fourier transform infrared spectroscopic methods-difference spectroscopy and photoselection

The direction of selected IR-transition moments of the retinal chromophore of bacteriorhodopsin (BR) and functional active amino acid residues are determined for light- and dark-adapted BR and for the intermediates K and L of the photocycle. Torsions around single bonds of the chromophore are found to be present in all the investigated BR states. The number of twisted single bonds and the magnitude of these torsions decreases in the order K, L, light-adapted BR, dark-adapted BR. In the last, only the C₁₄—C₁₅ single bond is twisted. The orientation of molecular planes and chemical bonds of such protein side chains, which are perturbed during the transition of light-adapted BR to the respective intermediates, are deduced and the results compared with the current three dimensional model of BR. Trp 86 and Trp 185 are found to form a rigid part of the protein, whereas Asp 96 and Asp 115 perform molecular rearrangements upon formation of the L-intermediate.     

Enzymatic cleavage of the epsilon-peptide bond in alpha- and epsilon-substituted glycyl- and phenylalanyl-lysine peptides

Lysine peptides, X-Lys-OH (Formula: see text) were synthesized, following classic or non-classic routes. Some bacterial and mammalian enzymes, endo- and exo-peptide hydrolases of the enzyme nomenclature type EC 3.4., were tested for their ability to split the epsilon-peptide bond in the above substrates. Kinetic constants (Km,kcat) were evaluated with leucine aminopeptidase from hog kidney and eye lens with aminopeptidase I from yeast. Aminopeptidase M (hog pancreas) and hog intestinal aminopeptidase were additionally examined for their Ki values with the above substrates in comparison to the classic protease substrate leucine p-nitroanilide. Especially the intestinal mucosa hydrolases are shown to be efficient in cleaving epsilon-peptide bonds.