Temperature coefficients of peptides dissolved in hexafluoroisopropanol monitor distortions of helices

Summary Temperature coefficients are widely used as an indication of solvent accessibility to amide protons. Low temperature coefficients are related to low accessibility and are often interpreted as evidence for intramolecular hydrogen bonding. Conformational shifts, i.e. the difference between chemical shifts of a particular residue in a structured and in a random-coil conformation, provide information on secondary structure. In particular, negative CH^α conformational shifts are often used to delineate the extent of helical stretches. NH conformational shifts show large oscillations within a helix that have been interpreted as the result of helix distortions affecting hydrogen bond lengths. In the ocurse of the study of differnet peptides that adopt a helical structure in the presence of the structure-inducing solvent hexafluoroisopropanol (HFIP), we have found a strong correlation between temperature coefficients and amide conformational shifts. However, contrary to the initial expectations, lower temperature coefficients were associated to amide protons involved in longer, and presumably weaker, hydrogen bonds. The correlation can be explained, however, assuming that, in helical peptides dissolved in HFIP, temperature affects the chemical shift of amide protons mainly by changing the average length of intramolecular hydrogen bonds and changes in solvent accessibility play only a secondary role under these experimental conditions. The pattern of temperature coefficients in helical peptides can therefore be used to identify short or long hydragen bonds causing bending of the helix axis.     

The optical activity and circular dichroic spectra of diacetylenic phospholipid polymers

Phospholipids (phosphatidylcholines) which contain a diacetylene group in a single acyl chain and within both acyl chains have been synthesized. Upon irradiation with ultraviolet light, both types of lipid crosslink via the diacetylene groups to produce coloured polymers. The colour arises form the conjugated double and triple bonds which make up the polymer backbone. These phospholipid polymers can exhibit optical activity, as shown by their circular dichroic spectra. The optical activity is thought to stem from asymmetric packing of the polydiacetylene chains, a packing of one particular screw sense being favoured by the chiral glycerol moiety of the lipid. The presence of an intrinsic membrane protein within the liposome structure affects the CD spectra of polymer produced by irradiation.     

The diet and distribution of Pentacoelum kazukolinda (Kawakatsu & Mitchell, 1984), a maricolan planarian with a freshwater ecology

Among the marine triclads or Maricola, the genus Pentacoelum represents one of the few exceptions in that species occur in brackish water or in freshwater. We examined specimens of a maricolan triclad that externally looked remarkably similar to the continental Spanish representatives of freshwater Pentacoelum hispaniense, albeit that these new samples came from habitats in Germany, the Netherlands, Mallorca and Japan. Comprehensive comparative morphological studies revealed that the animals from these populations are identical to a species described earlier from Hawaii, viz. Oahuhawaiiana kazukolinda Kawakatsu & Mitchell, 1984. It is argued that the species now should be called Pentacoelum kazukolinda (Kawakatsu & Mitchell, 1984) comb. nov. Remarkably, Dutch and German specimens of P. kazukolinda almost completely lack any signs of the presence of the lateral gonopore system, being the defining feature of their taxonomic family, the Bdellouridae. The reason for this reduction or even complete absence of this structure remains obscure. Nonetheless, morphological similarities and 18S rDNA sequences strongly suggest that all animals belong to the same species. Analyses of the mitochondrial gene sequences Cox1 and 16SrDNA of the gut content of P. kazukolinda revealed that the flatworm has a preference for different species of gastropods, while in one population annelids were detected. Our study suggests that gastropods may form the food refuge of P. kazukolinda. Circumstantial evidence suggests that the worldwide distribution of P. kazukolinda may result from human‐mediated transport of the aroid Colocasia esculenta and/or the introduced snail Potamopyrgus antipodarum. The use of P. antipodarum as a food resource may have facilitated the spread and establishment of new populations of P. kazukolinda.     

Incorporating pressure–volume traits into the leaf economics spectrum

In recent years, attempts have been made in linking pressure–volume parameters and the leaf economics spectrum to expand our knowledge of the interrelationships among leaf traits. We provide theoretical and empirical evidence for the coordination of the turgor loss point and associated traits with net CO₂ assimilation (A_n) and leaf mass per area (LMA). We measured gas exchange, pressure–volume curves and leaf structure in 45 ferns and angiosperms, and explored the anatomical and chemical basis of the key traits. We propose that the coordination observed between mass-based A_n, capacitance and the turgor loss point (π_tlp) emerges from their shared link with leaf density (one of the components of LMA) and, specially, leaf saturated water content (LSWC), which in turn relates to cell size and nitrogen and carbon content. Thus, considering the components of LMA and LSWC in ecophysiological studies can provide a broader perspective on leaf structure and function.     

Long range temporal correlations in EEG oscillations of subclinically depressed individuals: their association with brooding and suppression

Long-range temporal correlations (LRTC) in brain oscillations have been found to be associated with depression severity in clinically depressed patients. Less is known, however, about the relationships between LRTC and proneness to engage in depression-related cognitive emotion regulation (ER) strategies which characterize both clinically and subclinically depressed (SBD) people. In this study we applied detrended fluctuation analysis to the amplitude envelope of broad band, theta band, and alpha band spontaneous EEG oscillations of a group of SBD individuals and a group of non-depressed individuals (both groups from a sample of healthy adults, N = 120), to whom brooding and thought suppression questionnaires were administered. Between-groups differences were not found for any band scaling exponents at any brain location, but linear correlations pointed out several associations between exponents at frontal, central, parietal, temporal, and occipital sites and maladaptive ER strategies. These results suggest that alterations in brain dynamics are related with the proneness that depressive individuals show to engage in brooding and thought suppression in order to cognitively regulate their emotions.     

The effect of nuclease on transformation efficiency in Serratia marcescens

No differences in the efficiency of transformation were observed from both plasmid and chromosomal DNA in Serratia marcescens 2170 and an extracellular nuclease defective isogenic strain. The efficiency of transformation was the same for Escherichia coli 5K and E. coli containing a recombinant plasmid conferring the ability to synthesize a S. marcescens nuclease. From these results we conclude that the extracellular nuclease of S. marcescens 2170 is not the main cause of the low efficiency of transformation observed in this bacterium.