Co-oligopeptides of aromatic amino acids and glycine with variable distance between the aromatic residues. VII. Enzymatic synthesis of N-protected peptide amides

Several N-protected peptide amides, containing two aromatic residues spaced by one glycyl residue, have been enzymatically synthesized starting from P-Ar-OH and H-Gly-Ar-NH₂ (P is the protecting group and Ar is the aromatic residue) and using α-chymotrypsin as the catalyst for the coupling step. Reactions have been carried out in water solution, at room temperature, and afford yields ranging between 20 and 75% ca. This coupling reaction occurs in a much more restricted set of conditions than the hydrolysis reaction, e.g., only within a small pH range (ca. 6.5–7.5) and with particular buffering agents. The advantages and limitations of this type of reaction, compared with conventional coupling procedures, are discussed.     

Temperature dependence of the effects of some monohydric alcohols on the oxygen affinity of hemoglobin: Determination and analysis of thermodynamic parameters

We studied the effects of methanol, ethanol, iso-propanol, and n-propanol on the reaction of hemoglobin with oxygen at various temperatures. The analysis of the results in terms of the Monod-Wyman-Changeux model allowed determination of the overall contribution of the alcohols to the standard enthalpy and entropy differences between the T and R states of hemoglobin. A phenomenological approach allowed us to obtain separately the contributions related to the variations of the bulk dielectric constant of the solvent (bulk electrostatic contributions) and the contributions related to other effects (non-bulk-electrostatic contributions). The values of non-bulk-electrostatic contributions to ΔΔH and ΔΔS supported the suggestion that these contributions are mainly related to protein-solvent hydrophobic interactions.     

Etude de la dynamique des populations de cilies d'un torrent experimental pendant deux annees

The sampling of Ciliates performed in a little experimental torrent through two years, showed a great similarity of the two annual cycles. This similarity concerns both the species composition as well as the dynamics of the Ciliates populations. The basic species which affect the community structure are as follows: Ctedoctema acanthocrypta, Mesodinium acarus, Cyclidium glaucoma, Cinetochilum margaritaceum, Pleuronema coronatum, Lacrymaria pupula, Aspidisca costata and Holosticha vernalis. The dynamics of the ciliated Protozoa living in this environment seem to be influenced by the speed of the current, the temperature and the amount of dissolved organic matter in the water.

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Etude de la dynamique des populations de cilies d'un torrent experimental pendant deux annees

     

Co-oligopeptides containing two aromatic residues spaced by glycyl residues. X. Proton magnetic resonance study of co-oligopeptides of tryptophan and glycine

The ¹H-nmr spectra of co-oligopeptides of tryptophan and glycine with structure H-Gly-Trp-(Gly)_n-Trp-Gly-OH (n = 0–2) and those of several di- and tripeptides have been recorded at 360 MHz with CD₃OD solutions containing 0.1N NaOD. The assignment of resonance signals was generally possible by comparing the spectra of structurally related peptides with each other. In order to solve the remaining ambiguities in the assignment, H-(αL,βS)(α,β-d₂)Trp-OH, H-Trp-(αL,βS)(α,β-d₂)Trp-OH, and H-Trp-(δ¹,ε²,ζ²,ζ³,η²-d₅)Trp-OH have been prepared and their spectra compared with those of the undeuterated compounds. The distribution of rotamers around the χ₁ and (in two cases) χ₂ torsion angles of the side chains has been obtained from the vicinal coupling constants ³J and from the long-range coupling constants ⁴J. These data and an analysis of the chemical shifts of the Gly-C^α protons suggest that the orientation of the aromatic side chain is influenced by the following order of decreasing interaction with the functional groups at N- and C-side: -NH₂ > –NHCO– > –CONH–> –COO^?. This rule does not hold for the second Trp residue of di- and tripeptides containing the -Trp-Trp- sequence, which has tentatively been attributed to steric effects.     

In vitro T cell-mediated killing of Pseudomonas aeruginosa. I. Evidence that a lymphokine mediates killing

Previous studies have demonstrated in vivo that T cells can provide protective immunity, in the absence of antibody, against infection with the extracellular Gram-negative bacterium Immunotype 1 (IT-1) Pseudomonas aeruginosa. We established an in vitro system in which immune T cells, after reexposure to bacterial antigens and to macrophages, secrete a product that kills the bacteria. Although macrophages are required for in vitro killing, they function neither as antigen-presenting nor as phagocytic cells in this system. T cells from animals immunized against a different P. aeruginosa immunotype will not kill IT-1 organisms; but the supernatants produced by IT-1 immune T cells after exposure to macrophages and IT-1 P. aeruginosa organisms are nonspecifically effective in killing unrelated bacteria. Because the supernatants from immune T cells lose their bactericidal properties upon minimal dilution, we conclude that if this mechanism is active in vivo, it must play a role in local immunity.     

Lack of molecular relationships between lipid peroxidation and mitochondrial DNA single strand breaks in isolated rat hepatocytes and mitochondria

We investigated the molecular relationships between lipid peroxidation and mitochondrial DNA (mtDNA) single strand breaks (ssb) in isolated rat hepatocytes and mitochondria exposed to tert-butylhydroperoxide (TBH). Our results show that mtDNA ssb induced by TBH are independent of lipid peroxidation and dependent on the presence of iron and of hydroxyl free radicals. These data contribute to the definition of the mechanisms whereby mtDNA ssb are induced and provide possible molecular targets for the prevention of this kind of damage in vivo.     

Generalization of the QST framework in hierarchically structured populations: Impacts of inbreeding and dominance

Q_ST is a differentiation parameter based on the decomposition of the genetic variance of a trait. In the case of additive inheritance and absence of selection, it is analogous to the genic differentiation measured on individual loci, F_ST. Thus, Q_ST?F_ST comparison is used to infer selection: selective divergence when Q_ST > F_ST, or convergence when Q_ST < F_ST. The definition of Q‐statistics was extended to two‐level hierarchical population structures with Hardy–Weinberg equilibrium. Here, we generalize the Q‐statistics framework to any hierarchical population structure. First, we developed the analytical definition of hierarchical Q‐statistics for populations not at Hardy–Weinberg equilibrium. We show that the Q‐statistics values obtained with the Hardy–Weinberg definition are lower than their corresponding F‐statistics when F_IS > 0 (higher when F_IS < 0). Then, we used an island model simulation approach to investigate the impact of inbreeding and dominance on the Q_ST?F_ST framework in a hierarchical population structure. We show that, while differentiation at the lower hierarchical level (Q_SR) is a monotonic function of migration, differentiation at the upper level (Q_RT) is not. In the case of additive inheritance, we show that inbreeding inflates the variance of Q_RT, which can increase the frequency of Q_RT > F_RT cases. We also show that dominance drastically reduces Q‐statistics below F‐statistics for any level of the hierarchy. Therefore, high values of Q‐statistics are good indicators of selection, but low values are not in the case of dominance.