Synthesis and platelet aggregation inhibition activity of a series of enantiomeric bicyclo[3.2.0]heptane-6-oximinoacetic acids (1)

Opening of racemic epoxide (3) with (3S)- or (3R)-dimethyl-3-(dimethyl-t-butylsilyloxy)oct-1-ynyl aluminum gave two regioisomers, which were separated chromatographically. The separated regioisomers, themselves mixtures of chromatographically inseparable diastereoisomers, were converted into their dicobalthexacarbonyl complexes, which were easily resolved and isolated by chromatography. The individual diastereoisomers were deprotected to give bicyclo[3.2.0]heptan-3-ones, whose absolute stereochemistry was assigned using circular dichroism. One of these compounds, (1R,2R,3S,5R,3'S)-3-(3'-hydroxyoct-1'-ynyl)-bicyclo[3.2.0]++ +heptan-2-ol-6- oximinoacetic acid (11a) was 4.5 times more potent than PGE1 in inhibiting the ADP-induced aggregation of human platelets. The next most potent compound in this series was the "ent-15-epi" compound (11b), which was 0.034 times the potency of PGE1 in the platelet aggregation assay.     

Further studies on bilitranslocase,a plasma membrane protein involved in hepatic organic anion uptake

Bilitranslocase, a plasma membrane protein involved in bilirubin and other organic anion uptake by the liver, exhibits a high molecular weight (170 000) when isolated in the presence of deoxycholate. This value is decreased to approx. 100 000 if deoxycholate is not included in the isolation medium. Both preparations can be resolved into two kinds of subunit, α and β, of 37 000 and 35 500, respectively, by reduction with 2-mercaptoethanol and addition of sodium dodecyl sulfate. Under these conditions the two subunits are still capable of high-affinity sulfobromophthalein binding and, despite the presence of the detergent, may be isolated by preparative polyacrylamide gel electrophoresis still associated with the dye. It may be suggested that the physiological subunit composition of bilitranslocase is α₂-β.     

Lysis protein S of phage lambda functions in Saccharomyces cerevisiae.

The lambda S lysis gene was cloned into a Saccharomyces cerevisiae expression vector under GAL1 control. Induction with galactose in S. cerevisiae terminated cell growth and prevented colony formation. Several membrane proteins immunoreactive with anti-S antibody accumulated in the membranes, indicating that sodium dodecyl sulfate-resistant oligomers of S are formed, similar to those observed in the membranes of Escherichia coli cells killed by expression of the S gene. These observations suggest that the S gene product functions as a cytotoxic protein in the yeast cytoplasmic membrane as it does in the bacterial membrane.     

Stabilization of the ternary complex EF-Tu.GTP.valyl-tRNA by ammonium salts

In a search for crystallizing conditions for the ternary complex EF-Tu.GTP.valyl-tRNA^val, the influence of various salts on its stability has been examined by measuring the rate of deacylation of the aminoacyl-tRNA in the complex. The most striking result is the general higher stability in solutions of ammonium salts and, in particular, the enhancement of this effect by sulphate and citrate. Thus sodium sulphate and citrate lead to destabilization of the complex, as expected from conventional considerations of adding salt, whereas the corresponding ammonium salts stabilize the complex as shown, for example, by an increase in the half-life of the valyl-tRNA^val in the complex from about 20 hours to at least 300 hours in the presence of 1.2 M ammonium sulphate. These results suggest that ammonium sulphate and ammonium citrate might be very suitable precipitants for crystallization studies of the ternary complex.     

Nanisme écologique de deux espèces d'échinides irréguliers dans l'Hauterivien de la région de Castellane (Alpes-de-Haute-Provence)

Three species of irregular see-urchins form the settlement of a marly level (lower Hauterivian) of the Castellane area. Two of them are strongly smaller than the norm. Their stunting is prouved by ontogenic, mecanical, sedimentological and ecological arguments. The ecological grounds of stunting are discussed.     

Conformational properties of the N-terminal residues of S-peptide. I. The ribonuclease S′ system

The contribution of the 1–6 N-terminal sequence to the conformational properties of the S-peptide (the 1–20 sequence of ribonuclease A) was assessed by determining in the ribonuclease S′ system the helical content and the binding capability of synthetic [Orn¹⁰]-S-peptide analogs, in which lysine¹, glutamic² and threonine³ were progressively deleted, alanine⁴ and alanine⁵were alternatively replaced by serine, and alanine⁶ was substituted by serine or proline. Both the deletion of the three N-terminal residues and the alanine⁶/proline replacement produces the loss of the helical structure up to lysine⁷. No or minor effects are found in all other cases. From the comparison of the binding data, the energy for the conformational stabilization of the N-terminal region was calculated to amount to 1.4 kcal/mol. The results are discussed in comparison with the known x-ray data of the enzyme, with some predictive rules of secondary structure which were applied to this region and with the known phylogenetic variance of the residues in this region.     

The influence of amino acid side-chains on α-helix stability: S-peptide analogues and related ribonucleases S′

In order to determine the influence of amino acid side-chains on α-helix stability, in relation to the protein folding process, the coil-helix transitions of some synthetic [Orn 10]-S-peptide analogues, containing, in position 8, Phe, Tyr, Ile, Ala, cpGly² and Gly, were investigated by the technique of circular dichroism under two different sets of conditions. First, the transitions of the Speptide analogues in water/trifluoroethanol mixtures were recorded. From the pattern of the transitions and from the ellipticity values in 97% trifluoroethanol, the following increasing order of amino acids as α-helix formers was found: Gly < Tyr ≤ Phe < cpGly < Ala < Ile. This finding indicates that the conformational parameters (Chou & Fasman, 1974) of the residues in position 8 play an important but not exclusive role in α-helix stability, since the hydrophobicity of the side-chain (Nozaki & Tanford, 1971) of residue 8 exerts a strong influence. From the second approach, studying the capability of the S-peptide analogues to bind to S-protein, the following increasing order was found: (Gly, Ala) < Ile < cpGly < Tyr < Phe. This result reveals that the conformational parameters of the residues in position 8 play no role, whereas their hydrophobic character and side-chain interactions with surrounding residues in the S-protein portion are the determining binding factors. This finding explains the reason for the Phe8 invariance in RNAase A during evolution, and furnishes evidence for the relevant role of long-range interactions in the protein folding process.