Vibrational spectra of angiotensinamide 11, some constitutive peptides, and an analog, are presented. Comparison of data for the solid hormone with those for the subunits yielded amide vibrations of the former in the 500-1700 cm-l range. Angiotensinamide I1 was shown to adopt a preferential antiparallel , ! ? conformation in both the solid state and concentrated aqueous solutions. Conformational information obtained by other methods are discussed together with the present results.The data pertinent to the behavior of hormone specific receptor sites [l] delineate with increasing accuracy their mechanical character. They require an agonist of very precise structure, which by being locked in the receptor frame may be submitted to structural changes and induce conformational variations. To define the structure of the hormone itself before and after such an event in the receptor is an exciting challenge and the more so when the hormone is a peptide. Therefore, a better knowledge of the conformational characteristics of a peptidic hormone placed in a variety of conditions seems to be a preliminary step towards the solution of the problem defined above.I n addition it is very likely that no additive energy besides that resulting from interactions with the receptor, the surrounding medium and within the molecule itself, is required to give the hormone its specific structure.On these bases we undertook study of angiotensin I1 conformations as this molecule seemed to afford an interesting example of the environmental influence. As a matter of fact, this octapeptide of linear primary structure appears to adopt in dilute aqueous solution two main conformations detectable by di- [S]. The required folding of the molecule was assigned principally to the hydrophobic interactions between the 3 and 5 valine and the 8 phenylalanine side-chains and to the cis conformation of the histidine-proline peptide bond. Interestingly enough, dry films of angiotensin I1 yielded circular dichroism spectra also reminiscent of a pleated sheet structure. We wished to check these conclusions with independent techniques in order to assess the validity of the approach used.The present paper is devoted to a study of angiotensin I1 in the solid state and concentrated aqueous solutions by infrared and Raman spectroscopy.Early infrared work had suggested empirical relations between the vibration bands of the peptide bonds and the structure of polypeptides [9,10]. The theory of Rliyazawa [ll, 121, despite some possible inadequacies [ 131, rationalized the amide bands conformation correlations for homopolypeptides [14], and also permitted fruitful investigations of protein

141 (1984). La reaction du MgBrz anhydre sur le N-methylacetamide en solution dans CCll a t t t suivie par spectromttrie infrarouge mettant ainsi en evidence la formation progressive d'un compost d'addition NMA-MgBr?.SIMONE BLANCHARD and ANNE-MARIE TISTCHENKO. Can. J. Chem. 62, 141 (1984). The reaction between anhydrous MgBrz and N-methylacetamide (NMA) in CCI, solution has been studied by infrared spectrometry. The temporal variation of the spectra has been followed and the final spectrum is attributed to a compound of structure L'action des ions Mg" sur les protkines ou les peptides est un sujet de recherche de grande importance en biologie animale ou vkgttale. La spectrometric infrarouge nous a permis de suivre dans le temps la transformation du N-mCthylacCtamide (NMA) en solution dans CCl, en prtsence de MgBr, anhydre. Nous avons pu a l'aide du spectre infarouge du compost final montrer la formation d'un organomagnesien de formule: Conditions experimentalesLe bromure de magnesium anhydre est prepare par action du magnesium sur le dibromoithane en solution dans I'tther Cthylique anhydre. Le NMA est un produit Merck, redistill6 sous azote; le CCI, est un produit Merck, les dernikres traces d'eau sont CliminCes a I'aide de PZOs pulverulent; toutes les solutions sont faites en boite a gants a balayage d'azote. Les spectres infrarouge sont enregistrts sur un Perkin-Elmer 180.