Un modèle d'ontogenèse: La croissancede Toxaster granosus kiliani (Lambert)), échinide spatangoide du Valanginien

A complete study of the ontogeny of the irregular urchin Toxaster granosus kiliani (Lambert)) was achieved from an important lower cretaceous sample. In a first time, ontogenic variations of each character were analysed versus length chosen as size reference. This first step had shown that very important changes in shape take place during the development of the young urchin: increase in height, downward migration of the periproct, forward movement of the peristome… In a second time, a growth crisis was proved and described. Such a crisis occurs, from 12 mm to 16 mm length, as a momentary acceleration of the growth (i.e. the rate of growth increases during a short time). The reality of this crisis was demonstrated by both mathematical and biological ways and also by comparing with other actual and fossil populations. The whole of these results leads to a synthetical pattern of growth divided into three main stages which are successively a juvenile, a preadult and an adult stage. This division was proved also by a principal components analysis.     

Euphorigenic drugs: effects on the reward pathways of the brain.

This report summarizes a number of experiments designed to examine the changes in the threshold for intracranial self-stimulation (ICSS) in the rat after the administration of morphine and a number of narcotic agonist-antagonists, as well as three nonnarcotic drugs that have extensive nonmedical use (cocaine, d-amphetamine, and phencyclidine). The results of these experiments clearly indicate that morphine lowers the threshold for ICSS and, furthermore, there appears to be little or no tolerance to this effect. The only mixed agonist-antagonist that consistently lowered the ICSS threshold was pentazocine. Cocaine, d-amphetamine, and to a lesser degree, phencyclidine also lowered the ICSS threshold. These results suggest that the abuse liability of these agents may be directly related to their ability to sensitize the neural substrate involved with natural reward.     

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.     

Effect of ethyl acetate on the transport of sodium and glucose in the hamster small intestine in vitro.

The effect of ethyl acetate on Na+, water and glucose transport, as well as on glucose and electrolyte intracellular concentrations in everted and cannulated sacs of hamster jejunum, have been studied.Ethyl acetate, a substance that easily penetrates and delivers energy to the cell, strongly stimulates net glucose and Na+ transport. The explanation of the experimental results takes into account the possibility of the existence of an active extrusion of glucose at the level of the basolateral membrane of the enterocyte.     

Effect on ethyl acetate on the transport of sodium and glucose in the hamster small intestine in vitro

The effect of ethyl acetate on Na⁺, water and glucose transport, as well as on glucose and electrolyte intracellular concentrations in everted and cannulated sacs of hamster jejunum, have been studied.Ethyl acetate, a substance that easily penetrates and delivers energy to the cell, strongly stimulates net glucose and Na⁺ transport.The explanation of the experimental results takes into account the possibility of the existence of an active extrusion of glucose at the level of the basolateral membrane of the enterocyte.     

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.     

Studies on cytochrome c. XI. Circular dichroism studies on synthetic peptides related to the C-terminal region of baker's yeast iso-1-cytochrome c

Circular dichroism studies on synthetic peptides related to the C-terminal region of yeast iso-1-cytochrome c were carried out and compared with conformational studies on horse cytochrome c fragments. Evidence is presented for a weaker predisposition for ordered structure in the former peptides when compared with the corresponding region in horse cytochrome c. These findings agree with theoretical predictions and with observations that yeast and other mammalian type cytochromes c differ in several minor respects.     

Energy transduction in photosynthetic bacteria. VIII. Activation of the energy-transducing ATPase by inorganic phosphate

ATPase activity and ATP-induced energization of photosynthetic membranes from Rhodopseudomonas capsulata are stimulated by phosphate; the maximum stimulatory effect occurs at a concentration between 1 and 2 mM.The sensitivity of the ATPase to oligomycin increases in the presence of phosphate since all the P_i-stimulated activity is inhibited by this antibiotic. Aurovertin, which has no effect on ATPase in the absence of phosphate, inhibits completely the activity elicited by this anion.The addition of P_i induces a substantial increase in the V of ATPase activity without changing the affinity of the enzyme for ATP or ADP.Arsenate, at the same concentrations, produces effects very similar to those of phosphate. The stimulation by arsenate of the transfer of energy from ATP to the membrane suggests a non-hydrolytic role of this anion as a modifier of the ATPase activity.