L'ultrastructure du testicule de lézard vivipare (Reptile,Lacertilien)

Résumé Les cellules de Sertoli du testicule de Lacerta vivipara ont été étudiées en microscopie électronique chez des animaux récoltés entre le printemps et l'automne pendant deux années et chez des animaux hypophysectomisés en automne.Ces cellules contiennent de nombreuses mitochondries de petite taille à crêtes lamellaires, des ribosomes libres, un reticulum endoplasmique lisse moyennement développé, plusieurs petits dictyosomes formant l'appareil de Golgi, des liposomes et des microtubules. Elles renferment aussi de nombreux corps denses de grande taille qui paraissent être de nature lysosomiale. Le glycogène a été particulièrement étudié. Il est formé de particules dispersées au hasard dans le hyaloplasme. Des variations saisonnières dans la teneur en glycogène ont été notées. Chez les hypophysectomisés, les cellules de Sertoli contiennent de grandes quantités de ce métabolite dont les particules sont concentrées dans des petites plages, souvent autour des liposomes.Les rôles possibles des cellules de Sertoli sont discutés: soutien et apport de nourriture aux cellules germinales, production d'hormones et phagocytose des corps résiduels. Les variations de la teneur en glycogène sont également discutées.

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The fine structure of the lizard testisII. The Sertoli cells. Study of the glycogen

Summary Sertoli cells of the testis of Lacerta vivipara have been studied electron microscopically in animals obtained between spring and autumn during two years and in animals hypophysectomized in autumn.These cells contain numerous small mitochondria with lamellar cristae, free ribosomes, smooth endoplasmic reticulum moderately developed, several small dictyosomes forming the Golgi complex, lipid droplets and microtubules. There are numerous dense bodies of large size with an heterogeneous content which seem to be of lysosomial nature. Glycogen consists of particles dispersed at random in the hyaloplasm. Seasonal variations in the content of glycogen are noted. In hypophysectomized animals Sertoli cells contain large amounts of that metabolite whose particles are concentrated in small areas often around the lipid droplets.Possible role of the Sertoli cells concerning mechanical support and nutrition of the germinal cells, production of hormones and phagocytosis of residual bodies are discussed. The variations in the glycogen content are also discussed.

     

pH effect on electron microscopical contrast with iron salts solutions

Summary Various iron salts solutions have been used to contrast blocks of renal tissue prior to their dehydration and embedment. Pure ferric ammonio-sulphate solutions give a strong contrast of the nuclear chromatin, of the mitochondria and of the basement membranes, but the electron microscopical appearance of the tissue is bad, because of the acidity of the solution. At higher pH, obtained in mixtures of ferric ammonio-sulphate and potassium sodium tartrate, the preservation is improved, the contrast of the chromatin, of the mitochondria and of the membranes decreases from a pH of 4.5. On the contrary, the cytoplasmic matrix becomes more electron-opaque and takes a granular appearance.The advantages of the block-staining are discussed. Specimens contrasted by this method can be observed in the light microscope, after addition of haematoxylin to the dehydrating ethanol series. In that case, there is a complete similarity between the light-stained and the electron-contrasted areas. Moreover, the understanding of the contrast is easier after block-staining: in the case of iron, the metal is complexed by the phosphate and the sulphate radicals of the tissue, with a contrasting solution at a pH value up to 4.5. For higher pH values, the iron-tartrate complex ions play an important role, possibly even in the cationic sites of the tissue. They can thus be considered as anionic metallic contrasting agents.Dedicated to Prof. G. Wolf-Heidegger, on the occasion of his 60th birthday, this work has been supported by a grant (No. 3.141.69) of the Swiss Fonds national pour le développement de la recherche scientifique.Our warmest thanks are due to Prof. C Rouiller, who kindly accepted to give his critical evaluation and his advices on the raw material from which the present work has been extracted.The technical skill of Mr. Michel Delley and of Mr. Mrinal Chakrabarthy are gratefully acknowledged.     

Barnase has subsites that give rise to large rate enhancements.

Barnase is found to have a series of subsites for binding its substrates that confers large rate enhancements. Ribonucleotide substrates of the type Zp0Gp1Xp2Y have been synthesized, where p is phosphate, X, Y, and Z are nucleosides, and G is guanosine. G occupies the primary specificity site. The most important subsite is for p2, followed by that for Y. There appears to be no subsite for the Z or p0 positions. Occupation of the subsite for p2 gives rise to a 1000-fold increase in kcat/Km, composed of a 100-fold increase in kcat and a 10-fold decrease in Km. The Y subsite gives rise to further 20-fold increase in kcat/Km. Rates approaching diffusion control for kcat/Km are observed. kcat for the dinucleotide monophosphate GpU = 0.55 s-1, and Km = 240 microM; this compares with 53 s-1 and 20 microM for GpUp, and 3.3 x 10(3) s-1 and 17 microM for GpApA (the best substrate tested). Cleavage occurs at the 3'-phosphate of guanosine in all cases. There are differences in base specificity at the two subsites for X and Y downstream of the scissile bond. The binding energies of different substrates have been analyzed using thermodynamic cycles. These show that the contributions of the X and Y sites are nonadditive.     

Comparative Study of 35 Bacteriophages of Lactobacillus helveticus: Morphology and Host Range

This survey included 23 phages isolated from cheese whey and 12 temperate phages induced with mitomycin from their lysogenic host strains. All of the phages had an isometric head and a tail with a contractile sheath. In addition, short-tailed (160-nm-long) and long-tailed (260-nm-long) phages were distinguished. Short-tailed phages were by far the most widespread in French cheese factories (32 of the 35 phages studied). The study of phage relationships enabled two large groups of strains to be distinguished: those not or slightly sensitive to phages and those very sensitive to phages. There was an obvious relationship in the first group between phage sensitivity (or resistance) and the geographic origin of the strains. The second group contained primarily strains from large international collections and those isolated from commercial starters. The relationships among short-tailed phages, either temperate or isolated as lytic, suggest that lysogenic strains could be the major source of phages in French cheese factories.     

La theorie du controle du metabolisme controle et regulation

Resume La théorie du Contróle du Métabolisme (Kacser & Bums, 1973; Heinrich & Rapoport, 1974) décrit comment un réseau métabolique répond à de petites perturbations au voisinage d'un état stationnaire. Deux types de coefficients sont définis: les coefficients d'élaslicité qui quantifient les variations des vitesses des étapes isolées et les coefficients de contrôle qui expriment la réponse globale du réseau aux perturbations d'une étape donnée. Des relations entre ces coefficients existent (Relations de sommation et relations de connexion) (pour une revue, voir Mazat et Jean-Bart (1988)).On ne fait pas toujours la distinction entre Contrôle et Régulation. En fait, il apparait que la notion de régulation, si elle est trés claire lorsqu'il s'agit de la régulation de l'activité d'un enzyme, West plus du tout définie lorsqu'il s'agit d'un réseau métabolique dans son ensemble.Le but de l'exposé est de proposer une définition de la régulation d'un réseau métabolique et de montrer quelles relations peuvent exister entre lee phénomènes de régulation et la théorie du contrôle du métabolisme.Quelques exemples seront donnés pour illustration.     

Atypical human liver alcohol dehydrogenase: the beta 2-Bern subunit has an amino acid exchange that is identical to the one in the beta 2-Oriental chain

The "atypical' human liver alcohol dehydrogenase dimer, homogeneous for beta 2-Bern chains, was isolated from human liver of Caucasian individuals. It is derived from an allelic variant at the ADH2 gene locus and exhibits a considerably higher specific activity and lower pH optimum than its "typical' counterpart (isoenzyme beta 1 beta 1) from the beta 1-chain predominant in Caucasians. Peptides were prepared by trypsin or CNBr cleavage, and were purified by exclusion chromatography and reverse-phase high-performance liquid chromatography (RP-HPLC). Structural analysis of the peptides showed that beta 2-Bern differs at one position from beta 1. Thus, Arg-47 in beta 1 is substituted by His in beta 2-Bern. This exchange, compatible with a one-base mutation, explains all functional differences by altered interactions with the pyrophosphate moiety of the coenzyme. The difference is also structurally identical to that found for another atypical beta 2-subunit, the beta 2-Oriental type of major Asian occurrence, linking these two atypical forms of human alcohol dehydrogenase.     

Tertiary structure of animal tRNATrp in solution and interaction of tRNATrp with tryptophanyl-tRNA synthetase

Alkylation in beef tRNATrp of phosphodiester bonds by ethylnitrosourea and of N-7 in guanosines and N-3 in cytidines by dimethyl sulfate and carbethoxylation of N-7 in adenosines by diethyl pyrocarbonate were investigated under various conditions. This enabled us to probe the accessibility of tRNA functional groups and to investigate the structure of tRNATrp in solution as well as its interactions with tryptophanyl-tRNA synthetase. The phosphate reactivity towards ethylnitrosourea of unfolded tRNA was compared to that of native tRNA. The pattern of phosphate alkylation of tRNATrp is very similar to that found with other tRNAs studied before using the same approach with protected phosphates mainly located in the D and T psi arms. Base modification experiments showed a striking similarity in the reactivity of conserved bases known to be involved in secondary and tertiary interactions. Differences are found with yeast tRNAPhe since beef tRNATrp showed a more stable D stem and a less stable T psi stem. When alkylation by ethylnitrosourea was studied with the tRNATrp X tryptophanyl-tRNA synthetase complex we found that phosphates located at the 5' side of the anticodon stem and in the anticodon loop were strongly protected against the reagent. The alkylation at the N-3 position of the two cytidines in the CCA anticodon was clearly diminished in the synthetase X tRNA complex as compared with the modification in free tRNATrp; in contrast the two cytidines of the terminal CCA in the acceptor stem are not protected by the synthetase. The involvement of the anticodon region of tRNATrp in the recognition process with tryptophanyl-tRNA synthetase was confirmed in nuclease S1 mapping experiments.     

Nouvelle synthèse de spiro-orthoesters d-glucosidiques par photocyclisation stéréoselective d'hydroxyalkyl-d-glucosides

Irradiation of hydroxyalkyl glucosides in the presence of mercury(II) oxide and iodine gave glucosidic C-1-spiroorthoesters. Where the starting glycoside had CH₂OH, the cyclization was regio- and stereo-specific by α-attack. The C-1-spiroorthoesters were readily available in a “one-pot synthesis” starting from glucosyl halides.     

Crosslinking of elongation factor Tu to tRNA(Phe) by trans-diamminedichloroplatinum (II). Characterization of two crosslinking sites in the tRNA.

Trans-diamminedichloroplatinum (II) was used to induce reversible crosslinks between EF-Tu and Phe-tRNA(Phe) within the ternary EF-Tu/GTP/Phe-tRNA(Phe) complex. Up to 40% of the complex was specifically converted into crosslinked species. Two crosslinking sites have been unambiguously identified. The major one encompassing nucleotides 58 to 65 is located in the 3'-part of the T-stem, and the minor one encompassing nucleotides 31 to 42 includes the anticodon loop and part of the 3'-strand of the anticodon stem.