Applications biologiques de la spectroscopie Raman de résonance et de la spectroscopie micro-Raman de résonance

Advantages are given to illustrate the possibilities of resonance Raman spectroscopy in the studies of biological systems.A relation giving the size of porphinato-core of metalloporphyrins from resonance Raman frequency is proposed. It can be applied to heme, even in lived state.By illuminating the sample through a microscope, resonance Raman effect can be collected from 1 (μm)² of sample. Spectra of a vegetal-cell wall (pimento) and of a red corpuscle (hemoglobin) are shown as examples.     

Analyse des pedigrees et calcul des coefficients d'identité par les arbres géniques

Two genes in a pedigree are identical by descent if they are two copies of a common ancestor gene. To obtain an unambiguous definition of the set of genes, at some autosomal locus, any gene is defined as an ordered pair of zygotes: the zygote who carries the gene, and the parent who transmitted it. The natural ordered structure on the set of zygotes yields an ordered structure upon the set of genes. Any event of the mendelian segregation splits down the set of genes into non-overlaping classes of identical genes: when considered as an ordered sub-set of genes, each class is shown to have the algebraic properties of a tree. Given a sub-set ?? of genes, a family of exclusive events ensuring identity between all genes of ?? is identified as a family of genic trees with some property. This relationship between segregational events and genic trees is extended to the case where two sub-sets ?? and ??′ of genes are considered together. As a consequence, a general method is obtained to compute either identity coefficients involving any number of genes splitted into one or two identity classes, or the fifteen coefficients defined among four genes, whichever the relationships between zygotes and genes might be. Using this approach to deal with the allelic structure in a set of genes carried by related zygotes is suggested.     

Etude,par spectroscopie infra-rouge,de la conformation de quelques composés peptidiques modèles

Some experimental data are given on the infrared spectra between 3300 and 3500 cm^?1 of dilute solutions in carbon tetrachloride of three types of model compounds: CH_3?CONH-CH(R₁)-CONH(R₂), (I); CH₃-CON(CH₃)-CH(R₁)-CONH(R₂), (II) and CH₃-CONH-CH(R₁)-CON(R₂)₂, (III). In studying the N-H stretching bands, it was found that there are two types of intramolecular hydrogen bonds in these molecules; these result in two different cyclized conformations, C₅ and C₇, which contain respectively, five and seven atoms in the ring. By using model substances I, II, and III, in which the nitrogen atoms are unequally substituted, it is possible to identify the N-H stretching bands which are to be ascribed to the N-H oscillators included in the two different chelated conformations. It is found also that the stretching frequency of a free N-H oscillator depends upon the substituent on the nitrogen atom. Thus, it is possible to observe, with some of the model compounds I, four different absorption bands located at 3340, 3420, 3440, and 3460 cm^?1. The first two are ascribed to the N-H oscillators included in the H? bonds which lock the C₇ and C₅ conformations; the last two correspond to free N-H which differ with the substituent on the nitrogen atom.     

Modalités de l'inhibition de la croissance et de la synthèse des acides nucléiques des plantules de blé par l'acide abscissique

The growth of wheat seedlings (Triticum sativum) is inhibited by abscisic acid (ABA). The inhibition increases with the concentration of ABA (from 10^-6M to 5 × 10^-5M) and is stronger in the case of coleoptiles and first leaves than in roots. In contrast, naphthaleneacetic acid (ANA), at 10^-5M, exerts its greatest inhibitory effect on the roots. The inhibitory effect of ABA on coleoptiles can be partially overcome by kinetin and to a much smaller degree by gibberellic acid. Neither of these two compounds, at 10^-5M, had any effect on the ABA-induced inhibition of root growth. The RNA and DNA contents per plant organ are considerably reduced after treatment of the seedlings with ABA, particularly in the coleoptiles and the first leaves. The incorporation of uracil-2-¹⁴C and uridine T (G) into RNA of treated seedlings is reduced in the case of coleoptiles and first leaves, but considerably enhanced in roots. The mechanism of the action of ABA is discussed in the light of these results.     

Etude par spectroscopie infrarouge de la transformation hélice–chaîne statistique des polypeptides. II. Etude de l'interaction de quelques polypeptides à chaînes latérales polaires avec l'acide trifluoracétique

The various polymer–acid solvation possibilities occuring in the helix–coil transition process of polypeptides with polar side chains were systematically analyzed by infrared spectroscopy. The following samples have been considered: poly-γ-benzyl-L -glutamate (PBLG), alternating poly-γ-benzyl-D ,L -glutamate (PBD-LG), and poly-β-benzyl-L -as-partate (PBLA). The behavior of the amide A, I, II, and νC?O ester absorptions of each polymer dissolved in trifluoroacetic acid–chloroform mixtures was studied in depth. The classical assumptions concerning the interaction between a polypeptide and a proton donor solvent are discussed. This interaction was previously proposed in a theoretical model of helix–coil transition. For PBLG, the spectral characteristics of the cooperative transition are evidenced by the amide bands. These bands also show main chain–acid hydrogen bonding (I) Quantitative analysis of phenomenon (I) was performed in order to localize the “binding sites” of the polymer. In agreement with the theory, only the complexation of peptide units belonging to random coil and terminal helical regions were observed. However, in contrast to the theory in which the association constants KCO and KNH of these residues are generally kept equal, the present results have shown that the main binding site is the carbonyl group (KNH ? 0 or « KCO ). The behavior of the polar side chains of these polypeptides were analyzed during the transition. Similarly to the peptide backbone, they bind the acid by hydrogen bonding (II) Furthermore, this association is more important when the side chains are localized in the coiled regions than in the helical ones. This result suggests, by analogy with the main chain behavior, that the helix–coil transition theory should take into account two more association constants for polar side chains, namely k₁ for the helical regions and k₂ > k₁ for the coiled ones.     

Conformations et spectre Raman de l'acide ribonucléique de transfert, tRNA

The structure of yeast tRNA^Asp in aqueous solution has been studied in sight of Raman spectra recorded between 5 and 82°C. A conformational change is evidenced at 20°C and an endomelting is found around 70°C. This melting temperature, much higher than in tRNA-^Phe (near 50°C) is interpreted by the presence of a higher number of G-C bases in tRNA^Asp.At a same temperature, the Raman spectrum of a tRNA^Asp crystal is quasi-identical than that of an aqueous solution, indicating a high structural similarity except bands corresponding to G,C bases which show a more effective stacking of these bases in the solid.     

Étude de la fixation de faible affinité du Ca par les membranes externe et interne des mitochondriest et par le réticulum endoplasmique lisse et rugueux de foie de rat

Two classes of low-affinity Ca²⁺-binding sites have been shown to exist. One type dissociates as pH rises, thereby increasing the amount of bound Ca²⁺. The other type, which does not change in number, has an affinity for Ca²⁺ which is dependent on ionic strength. The former is possibly a phospholipid, the latter possibly a protein.Under our experimental conditions, the inner mitochondrial membrane contained binding sites of the second class ony while other membranes contain both types. Rough endoplasmic reticulum contains yet another class of sites at the ribosomal level.

Résumé

L'existence de deux catégories de sites de fixation de faible affinité du Ca²⁺ a été mise en évidence. Les uns se dissocient de plus en plus quant le pH s'éléve permettant une augmentation des quantités de Ca²⁺ fixé, les autres sont invariables en nombre, mais leur affinité pour le Ca²⁺ est dépendante de la force ionique du milieu. Les premiers pourraient étre de nature phospholipidique, les seconds de nature protéique.Dans nos conditions expérimentales, la membrane interne des mitochondries possède uniquement des sites de la seconde catégorie. Les autres membranes renferment simultanément les deux sortes de sites. Le réticulum endoplasmique rugueux possède des sites supplémentaires au niveau des ribosomes.     

Variation du taux d'acide abscissique chez deux variétés de poiriers, la Passe-Crassane et la Doyenne du Comice, en fonction de l'induction de la parthénocarpie par l'acide gibbérellique

The content of abscisic acid in the developing fruits of two cultivars of pear (Pyrus communis L.) was determined by UV spectrophotometry and by a colorimetric method based on the possibility of the lactone corresponding to abscisic acid to give a purple colour when sodium hydroxide is added. The young fruits were harvested either from trees treated with gibberellic acid (GA₃), for the purpose of inducing parthenocarpy, or from untreated trees. High levels of abscisic acid were associated with abortion and abscission of young fruits (June drop). There was little difference between fruits of GA₃-treated and untreated trees of the cultivar Passe-Crassane. In the other cultivar, ‘Doyenne du Comice’, the level of abscisic acid in the fruits of GA₃-treated trees was about twice as high as in control fruits and seemed to be directly related to the number of fruits per tree.     

Cartographie de restriction comparée de la séquence d''ADN hautement répétée coupée par Bam HI chez Papio papio et P. cynocephalus

Highly repeated DNA sequences from two baboon species (Papio papio and P. cynocephalus) have been compared using restriction endonucleases. The two species share a 343 base pairs tandemly repeated DNA, that is cut once by Bam HI. Papio cynocephalus differs from P. papio by loss of an EcoRI star site in the repeated sequence.