Pierre Pellegrin

Cell cycle dependent toxicity of an amphiphilic synthetic peptide

The cytotoxic properties of an amphiphilic synthetic peptide are presented. Comparative analysis of proliferating, differentiated and confluent H9C2 adherent cells and L1210 cells in suspension shows a correlation between toxicity and cell stage (proliferating cells). Electrophysiological measurements on Xenopus laevis oocytes bathed in the peptide also demonstrated the induction of cationic currents, which is voltage and phosphate dependent. These results allow us to hypothesize that the observed toxicity is related to membrane hyperpolarization of proliferating cells at the G1/S cell cycle phase transition.

Mathematics and the Physical World in Aristotle

I would like to start with a historical question or, more precisely, a question pertaining to the history of science itself. It is a widely accepted idea that Aristotelism has been an obstacle to the emergence of modern physical science, and this was for at least two reasons. The first one is the cognitive role Aristotle is supposed to have attributed to perception. Instead of considering perception as an origin of error (even if this may be the case in exceptional situations, if the perceiving subject is sick for instance), Aristotle thinks that our senses provide us with a reliable image of the external world. The perceptive knowledge is a kind of knowledge in its own right, and the theoretical knowledge is, in fact, the continuation of the perceptive knowledge in some way. The second reason is the presumed inability of the Aristotelian philosophers to apply mathematics to the physical world. This was a formidable obstacle because modern physics came to be but as a mathematical physics. Aristotelianism had therefore to be, so to speak, superseded by the Platonic movement that originated in Florence around Ficino in order to give modern physics the conditions of its appearance. Galileo had to say that “Nature is written with mathematical letters” and Descartes that “our senses do not teach us what things are, but to what extent they are useful or harmful to us”. Alexandre Koyre is right to consider Galilean physics to be basically Platonic. The theoretical justification Aristotle offers for the impossibility of a convergence between mathematics and physics seems to be based on some fundamental features of his philosophy, i.e. he rejects the Platonic conception of a unique science, encompassing all things, and replaces it with the doctrine of the incommunicability of genera, whose corollary is that there is but one science for each genus.

RETINOL AND RETINOIC ACID VECTORIZATION WITH A SYNTHETIC PEPTIDE FORMING β‐BARREL STRUCTURE

We built a peptide which autoassociates as beta-barrels (under defined conditions), The secondary structure is elucidated by CD, PTIR and fluorescence spe@oscopy measurements. When phosphate ions are present (> for&f, pH 7.2) and for peptide concentrations below 5mM, the peptide is autoassociated as antiparallel g-sheets. The fluorescence studies concerning all tram retinol and all tram retinoi’c acid with this peptidic structure show that~ ten antiparailel strands beta barrels bind retinolds with a dissociation constant (Ko = 3.10” mo1.l’) very close to natural ~Retino’ids Binding Proteins (Cogan LJ., Kopelman M., Mokady S. and Shi&zky M.(1976) Eur.J. &&em. ,65,?1-78 ; LaLonde J. M. , Bemlohr D. A. and Banaszak L. J.(I994) FASEB J. 8, 1240-1247). Thus, we mimic perfectly endogenous proteins which bind retino’ids.