Heterodetic bicyclic decapeptide cyclo (Glu1 -Leu2 -Pro3-Gly4-Ser5-Ile6-Pro7-Ala8) cyclo-(1γ-5β) Phe9-Gly10

Bycyclic peptides are useful model molecules that can mimic the constrained local folding of a great number of natural peptides and proteins, such as ionophoric peptides, enzyme active site, and ligand-receptor active site. The synthesis of the bicyclic title compound with the liquid phase method is described with experimental details. Of particular interest is the heterodetic closure of the second ring. The peptide showed a complexing activity with metal cations like Ba²⁺, Ca²⁺, and Mg²⁺ . The free bicyclic peptide conformation in solution has been studied by means of NMR spectroscopy and a plausible structure model worked out with model building on NMR constraints is proposed.     

ESBRA-NORDMANN 1996 AWARD LECTURE: ETHANOL DRINKING BEHAVIOUR IN SARDINIAN ALCOHOL-PREFERRING RATS

Sardinian alcohol-preferring (sP) rats have been selectivelybred for high ethanol preference and consumption over 16 yearsand 39 generations. The present paper briefly reviews some recentstudies from this laboratory characterizing ethanol drinkingbehaviour in this rat line. Under the two-bottle regimen offree choice between 10% (v/v) ethanol and water, sP rats consumedaily >4 g of ethanol/kg and avoid water almost completely.Relevant features of ethanol drinking behaviour in sP rats are:(a) attainment of high ethanol intake from the first day ofexposure to ethanol, suggestive of an immediate disclosure andacquisition of ethanol reinforcement; (b) titration of dailyethanol intake in distinct binges during the nocturnal phaseof the light/dark cycle, indicative of their ability to regularizeboth ethanol dose and administration time; (c) achievement ofpharmacologically relevant blood ethanol levels at each drinkingepisode; (d) substitution of the calories provided by ethanolfor a part of those taken from food; (e) maintenance of constantethanol intake (in g/kg/day) in the presence of ethanol concentrationsvarying from 7 to 30% (v/v). These results suggest that voluntaryethanol intake in sP rats is sustained by the search for specificpharmacological effects of ethanol. Anxiolysis is likely tobe one of these effects; indeed, voluntarily consumed ethanolreversed the innate, high levels of anxiety in sP rats. Theseresults portray sP rats as a valid model for investigating theassociation between ethanol drinking and anxiety. Finally, thebreeding programme as well as results of neurochemical studiesare also described.     

Synthesis of cyclic tryptathionine peptides

The helicity of the tryptathionine moiety of the phallotoxins has been recognized by comparison with cyclic tryptathionine tripeptides. In order to investigate the influence of the configuration of the component amino acids on the conformation of the cyclic peptides, six analogue thioether tripeptides containing L- and D-alanine and L- and D-cysteine, respectively, have been synthesized. The CD spectra of the peptides are very similar to each other, showing mirror images of the CD of phalloidin and, therefore, negative helicity. The spectra of the D-cysteine containing compounds differ from the L-cysteine containing compounds by their weakly positive ellipticity values around 270 nm. The cyclization reaction of Boc-Hpi-D-Ala-D-Cys(STrt)OCH₃, along with the cyclic tripeptide, afforded a cyclic hexapeptide by dimerization. The CD spectrum of the dimer is very similar to that of phalloidin, thus pointing to a positive helicity of its two tryptathionine moieties. The dimeric thioether peptide forms a rather strong complex with Cu²⁺ ions.     

Internal Cardioversion of Chronic Atrial Fibrillation in Patients

Transvenous internal cardioversion of chronic AF using a right atrium (RA) coronary sinus (CS) vector requires more energy than cardioversion of paroxysmal AF. Chronic AF is not terminated in 25% of patients using biphasic shocks up to 10 J. We therefore evaluated efficacy, safety, and tolerability of internal cardioversion using a "unipolar' configuration (RA to skin patch) and biphasic shocks in patients with long-lasting AF and different heart disease. In each patient, biphasic R have synchronous shocks were delivered between a large defibrillating surface area electrode in the RA and a skin patch in the left prepectoral position. Defibrillation protocol started with a test shock of 0.4 J. Shocks were repeated and increased until termination of AF or a maximum of 34 J. Sedation was used when the patient described the shock as painful. This study included 11 patients with a mean age of 67 ± 8 years (range 56–83). AF duration was ± 1 month in all patients with a mean duration of 11 ± 11 months (range 2–36). Underlying heart disease was present in all patients and the mean left atrial dimension was 43 ± 9 mm (range 26–57). AF was terminated in 10 of 11 patients (91 %) with a mean delivered energy of the successful shocks of 18.7 ± 8.7 J (median energy 16.9 J; range 7.3–32.5) and a mean leading edge voltage of 564 ± 129 V. The mean shock impedance at the defibrillation threshold was 71 ± 13 Ω, (range 59–103). A total of 131 shocks were delivered without any complication and proarrhythmia episodes. We conclude that low energy "unipolar" internal cardioversion is a simple, safe, and effective technique for termination of chronic AF in patients with heart disease. The procedure is often tolerated under light sedation.     

Crystallographic characterization of geometry and conformation of TOAC,a nitroxide spin-labelled Cα,α-disubstituted glycine,in simple derivatives and model peptides *

The molecular and crystal structures of one derivative and two oligopeptides of TOAC, a nitroxide spin-labelled C^αα-disubstituted glycine, have been determined by X-ray diffraction. The derivative is the 5(4H)-oxazolone from Piv-TOAC-OH; the oligopeptides are Z-TOAC-(L-Ala)₂-NHtBu sesquihydrate and p BrBz-TOAC-(L-Ala)₂-TOAC-L-Ala-NHtBu hemihydrate. Incipient and fully developed right-handed 3₁₀-helical conformations are formed by both independent molecules in the asymmetric unit of the terminally blocked tripeptide amide and the terminally blocked pentapeptide amide, respectively. The average geometry and preferred conformation for the piperidine ring of the TOAC residues are also discussed in detail. © Munksgaard 1996.     

Probing the structure of human growth hormone by limited proteolysis

Digestion of human growth hormone (hGH) with the Glu-specific protease from Staphylococcus aureus V8 was performed at 20-22°C or 37°C at a 1:20 ratio (by weight) at pH 7.8 with or without 0.2% SDS. There are 14 Glu-residues evenly distributed along the polypeptide chain of hGH as possible sites of proteolytic cleavage of V8-protease. The pattern of fragmentation of hGH was analyzed by electrophoresis and reversed-phase HPLC, and the identity of the proteolytic fragments isolated to homogeneity was established by their partial sequencing and amino acid analysis after acid hydrolysis. Kinetic analysis of the proteolytic digestion process allowed to establish that initial nicking of the protein occurs at Glu³³ and subsequently at Glu⁵⁶ and Glu⁶⁶. Much slower cleavages occur at G1u³⁰ and Glu¹⁸⁶. These cleavage sites are located at chain loops in the hGH molecule, and in particular outside the helical segments of the four-helix bundle of the crystal structure of hGH. Fragments 1-33 and 67-191 comprising entirely the N-terminal helix and the three C-terminal helices of hGH, respectively, were isolated to homogeneity in amounts useful for subsequent conformational and functional studies. The results of this study and of previous ones [Li, C.H. (1982) Mol. Cell. Biochem. 46 , 31-41] describing limited proteolysis of hGH by various proteases have been interpreted on the basis of the three-dimensional structure and dynamics of hGH. Overall, it is shown that proteolytic enzymes preferentially cleave hGH at exposed and flexible loops only, thus emphasizing the fact that proteases can be used as reliable probes of protein structure and dynamics. © Munksgaard 1995.     

Suggestions of Altered Balance: Possible Equivalence of Imagery and Perception

Hypnotic suggestions describing an altered perception induce congruent changes in the subject’s experience and behavior. However, it is not known whether an implicit suggestion, only indirectly referring to an altered perception, induces a behavioral response corresponding to that of the real situation. In this study, an implicit suggestion of backward falling (IMP) was given to high hypnotizable participants not exposed (W-Highs) and exposed (H-Highs) to a hypnotic induction and a group of low hypnotizable individuals (W-Lows). Their posture was evaluated through an elite system. The results after the IMP were compared with those after an explicit suggestion of backward falling (EXP). In both W-Highs and H-Highs, the IMP elicited the backward body sway expected in the corresponding real situation, whereas no response was found in W-Lows. The results are discussed in terms of a possible equivalence of imagery and perception or of a lack of the motor inhibition normally associated with motor imagery.