Biosynthese in vitro d'iodothyronines a partir du diiodo-3,5-L-tyrosyl-diiodo-3,5-L-tyrosine

In vitro biosynthesis of iodothyronines from diiodo-3,5-L-tyrosyl-diiodo-3,5-L-tyrosine A comparative study of two types of in vitro synthesis of iodothyronines has been done from 3,5-diiodotyrosine and from diiodo-3,5-L-tyrosyl-diiodo-3,5-L-tyrosine (Tyr(I)₂-Tyr(I)₂) (equimolecular in tyrosyl rings).Incubations are made with rat thyroid gland minces in Eagle's medium or with thyroid microsomal fraction.Synthesis of thyroid hormones from Tyr(I)₂-Tyr(I)₂ is faster and more important than from diiodo-3,5-L-tyrosine (Tyr(I)₂).A mechanism of iodothyronine formation via Tyr(I)₂ - Tyr(I)₂ and different from the one occuring for Tyr(I)₂ is suggested.     

In vitro biosynthesis of iodothyronines from diiodo-3,5-L-tyrosyl-diiodo-3,5-L-tyrosine (author's transl)]

A comparative study of two types of in vitro synthesis of iodothyronines has been done from 3,5-diiodotyrosine and from diiodo-3,5-L-tyrosyl-diiodo-3,5-L-tyrosine (Tyr(I)2-Tyr(I)2) (equimolecular in tyrosyl rings). Incubations are made with rat thyroid gland minces in Eagle's medium or with thyroid microsomal fraction. Synthesis of thyroid hormones from Tyr(I)2-Tyr(I)2 is faster and more important than from diiodo-3,5-L-tyrosine (Tyr(I)2). A mechanism of iodothyronine formation via Tyr(I)2-Tyr(I)2 and different from the one occuring for Tyr(I)2 is suggested.     

Induction by 3, 5, 3′ l-triiodothyronine of l-ornithine decarboxylase in rat heart muscle

Injection of 3,5,3′ l-triiodothyronine (15 μg/100 g) induces a biphasic enhancement of rat heart ornithine decarboxylase (EC. 4.1.17) activity after 4 and 21 hours. This induction is observed after each daily injection, but to a lesser extent.The properties of partially purified basal enzyme and induced enzyme, at 21h, after single injections have been compared.

1) Affinity for ornithine is the same for both enzymes, but affinity for pyridoxal-phosphate is 40-fold higher for the induced one.

2) Thermostability studies suggest that basal and induced enzymes have different conformations.

3) The two enzymes have similar immunoreactivity.

4) The comparisons of the time-dependent activity curve after injection and of the antigen/activity ratio suggests that triiodothyronine induces the synthesis of new molecules of enzymes and that an inhibition of the enzyme activity also occurs which explains the biphasic induction.

Mechanism of an in vitro biosynthesis of thyroid hormones from 3,5-diiodo-l-tyrosyl-3,5-diiodo-l-tyrosine: II. Role of the pyridoxal phosphate and of the peroxidase

In this paper several details of the in vitro pathway of synthesis of hormones from 3,5-diiodo-l-tyrosyl-3,5-diiodo-l-tyrosine, I₂Tyr-I₂Tyr, have been investigated.

1. 1. We showed by incubations of I₂Tyr-I₂Tyr with a tautomerase that a phenylpyruvic form of the dipeptide did not occur.

2. 2. The reaction required pyridoxal phosphate: this coenzyme acts as an activator of the molecule.

3. 3. The peroxidase is involved in the reaction, since in the absence of a hydrogen peroxidase-generationg system there is no synthesis of iodothyronines when I₂Tyr-I₂Tyr is used as a precursor.

The significance of these findings is discussed and in particular it is concluded that such a mechanism cannot be transposed completely to conditions in vivo.     

Mechanism of an in vitro biosynthesis of thyroid hormones from 3,5-diiodo-l-tyrosyl-3,5-diiodo-l-tyrosine: I. Manifestation of the elimination of the alanine side chain of the N-terminal diiodotyrosine

It was previously shown that 3,5-diido-l-tyrosyl-3,5-diiodo-l-tyrosine, I₂Tyr-I₂Tyr, acts as a precursor in the in vitro synthesis of thyroid hormones, and a mechanism of syntheis was proposed.We investigated this pathway by incubations of I₂Tyr-I₂Tyr with microsomal solubilized thyroid proteins. I₂Tyr-T₂Tyr was doubly labeled: iodinated with ¹³¹I on the ring and tritiated either on the alanine side-chain of the N- or C-terminal diidotyrosine. It is shown that only the C-terminal alanine participates in the synthesis, the N-terminal alanine being eliminated.The result proved that I₂Tyr-I₂Tyr acts as precursor through a mechanism which is different from the one involving I₂Tyr. This mechanism consists of: Schiff base formation with pyridoxal; free radical formation and cyclization; peptide bond cleavage and removal of the pyridoxal · alanine complex.     

A new locality of Late Cretaceous snakes, mammals and other vertebrates in Africa (western Libya)

s sp. nov. (Reptilia sp. nov. (Reptilia, Serpentes, Simoliopheidae) is described from the Upper Cretaceous ‘unnamed’ beds of the Mizdah Formation (Santonian-Campanian) at Draa Ubari in western Libya. The accompanying fauna consists of an undetermined mammal represented by a caudal vertebra, of hybodontoid, ganopristid and lamnoid sharks, as well as dipnoans, lepisosteids, pycnodonts, enchodontids, turtles, crocodiles and ?dinosaurs.

Résumé

Une nouvelle localité de serpents, mammifères et autres vertébrés du Crétacé supérieur en Afrique (Libye occidentale). s sp. nov. (Reptilia sp. nov. (Reptilia, Serpentes, Simoliopheidae) est décrit dans des grès de la formation Mizdah (Santonien-Campanien), à Draa Ubari en Libye occidentale. Les mêmes couches ont livré une vertèbre caudale de mammifère indéterminé, ainsi que des restes de requins hybodontoïdes, ganopristidés et lamnoïdes, de dipneustes, lépisostéïdes, pycnodontes, enchodontidés, tortues, crocodiles et? dinosaures.     

From the cholinergic gene locus to the cholinergic neuron

The cholinergic gene locus (CGL) was first identified in 1994 as the site (human chromosome 10q11.2) at which choline acetyltransferase and a functional vesicular acetylcholine transporter are co-localized. Here, we present recent neuroanatomical, developmental, and evolutionary insights into the chemical coding of cholinergic neurotransmission that have been gleaned from the study of the CGL, and its protein products VAChT and ChAT, which comprise a synthesis-sequestration pathway that functionally defines the cholinergic phenotype.

Résumé

Le locus génétique cholinergique (cholinergic gene locus, CGL) a été identifié en 1994 et regroupe les gènes de la choline acétyltransférase et d'un récepteur vésiculaire d'acétylcholine (chromosome humain 10q11.2). Nous présentons ici des données sur la neuroanatomie, le développement et l'évolution de la neurotransmission cholinergique obtenus à partir de l'étude du CGL et de ses produits protéiques, VAChT et ChAT: ce système de synthèse-séquestration définit fonctionnellement le phénotype cholinergique.     

Nouveaux restes postcrâniens d'hominoidea du miocène inférieur de napak, ouganda hommage à w. w. bishop

During reorganisation of the palaeontology collections at the Department of Antiquities and Museums, Kampala by the Uganda Palaeontology Expedition, several primate postcranial remains from Napak, an Early Miocene site, were found. Several large limb bones are attributed to Proconsul major, already known, already known from the locality on the basis of dental and gnathic remains, but hitherto poorly known postcranially. One specimen belongs to a smaller species of hominoid not represented at Napak by teeth and jaws. Both hominoids show quadrupedal and climbing adaptations, but they differ from each other. Thus Proconsul major praticed ‘power’ climbing whereas the smaller hominoid would have been more ‘agile’. In both cases, the hominoids moved frequently between the trees and the ground, and both were well adapted to their palaeoenvironment, which was dry forest. A further important result of this study is that the postcranial remains of r indicat indicate that it was heavier than had previously been envisaged on the basis of its dental remains. It would have weighed about the same as female gorillas, between 75 and 90 kg. The small species weighed about 20 kg.

Resumé

Lors d'un réaménagement des anciennes collections paléontologiques de l'Uganda Museum, des restes postcrâniens de primate provenant du site Miocène inférieur de Napak ont été retrouvés. Certaines pièces de grandes dimensions sont attribuées à Proconsul major, déjà signalé sur le site à partir de restes dentaires et gnathiques, mais dont l'anatomie postcrânienne était mal connue. D'autres spécimens sont rapportés à un Hominoidea de plus petite taille et non représenté par des dents ou des mâchoires. Les deux hominoïdes montrent des caractéristiques de quadrupèdes pratiquant le grimper mais de façons différentes. Alors que r pratique un gr pratique un grimper puissant, l'Hominoidea de petite taille pratique un grimper plus agile. Quoi qu'il en soit, ces deux espèces se déplaçaient souvent et activement au sol et dans les arbres. Ils vivaient dans une forêt sèche. Cette étude confirme que r, Hominoidea de, Hominoidea de grande taille, avait une masse corporelle plus importante que celle envisagée auparavant à partir des mesures dentaires. Il devait avoir une masse équivalente à celle d'un gorille femelle et peser entre 75 et 90 kg. L'espèce plus petite, quant à elle, aurait pesé 20 à 25 kg environ.     

Synthesis and glycogen phosphorylase inhibitory activity of N-(β-d-glucopyranosyl)amides possessing 1,4-benzodioxane moiety

A series of N-(β-d-glucopyranosyl)amides 5d–i were synthesized by PMe₃ mediated Staudinger reaction of O-peracetylated β-d-glucopyranosyl azide (1) followed by acylation with carboxylic acids 3d–i and subsequent Zemplén deacetylation. The new compounds were tested for their inhibitory activity against rabbit muscle glycogen phosphorylase and the structure–activity relationships of these compounds are also discussed in this paper.     

Revision of the Early Miocene Hyracoidea (Mammalia) of East Africa

Three genera of hyracoids were recorded from the Early Miocene of East Africa by Whitworth [18], but there has been considerable divergence of opinion about their status. Despite differences in cranial and dental morphology from Megalohyrax and Bunohyrax, Whitworth [18] classified two species in these genera that are recorded from much earlier deposits (Early Oligocene) in the Fayum, Egypt. One of his genera (Meroehyrax) was new. His classification has been the subject of debate, with some researchers [6,13] doubting the hyracoid status of one of his species (Bunohyrax sp), and changing the generic status of another (Megalohyrax championi). Meyer [6] recorded a fourth genus (Prohyrax) from Kenya, linking it to material from Namibia described by Stromer [16,17]. New samples of two hyracoid species collected by the Uganda Palaeontology Expedition throw light on their systematic position and taxonomy. It is concluded that there are three hyracoid genera (Afrohyrax, Brachyhyrax and Meroehyrax) in the Early Miocene deposits of East Africa, the first two of which are new. A fourth genus (Prohyrax) occurs in southern Africa, but is not reliably known from East Africa. To cite this article: M. Pickford et al., C. R. Palevol 3 (2004).

Résumé

Révision des Hyracoidea (Mammalia) du Miocène inférieur de l'Afrique de l’Est. Trois espèces d’Hyracoidea ont été signalées dans le Miocène inférieur d’Afrique orientale par Whitworth [18]. Malgré des différences importantes de la morphologie cranio-dentaire, deux des espèces kenyanes étaient classées dans Megalohyrax et Bunohyrax, genres connus dans les dépôts beaucoup plus anciens du Fayoum en Égypte. Le troisième genre décrit par Whitworth (Meroehyrax) était nouveau. La classification proposée [18] a été débattue ; certains auteurs [6,13] ont remis en cause le statut d’Hyracoïde d’une de ses espèces et ont modifié le statut générique d’une autre. Meyer [6] a signalé un quatrième genre (Prohyrax) au Kenya, sur la base des ressemblances avec le genre namibien décrit par Stromer [16,17]. De nouveaux spécimens récoltés par l’Uganda Palaeontology Expedition permettent d’éclaircir la position systématique et la taxonomie de deux des espèces. Nous concluons qu’il n’existe que trois genres d’Hyracoïdes dans les dépôts du Miocène inférieur d’Afrique orientale (Afrohyrax, Brachyhyrax et Meroehyrax), dont les deux premiers sont nouveaux. Par ailleurs, un quatrième genre (Prohyrax) est connu d’Afrique australe. Pour citer cet article : M. Pickford et al., C. R. Palevol 3 (2004).     

Theropithecus atlanticus (Thomas, 1884) (Primates: Cercopithecidae) from the late Pliocene of Ahl al Oughlam, Casablanca, Morocco

The site of Ahl al Oughlam near Casablanca, Morocco, dated to ca. 2·5 Ma, has yielded a good sample of Theropithecus atlanticus (Thomas, 1884), a North African late Pliocene species previously known only by its holotype, a lower molar from Algeria. Theropithecus atlanticus, which can now be much better defined, is clearly distinct from other species of the genus, which is thus more diverse than previously thought. The mandible of T. atlanticus has a very characteristic deep and long post-molar sulcus and a deep and well excavated supra-lateral triangular depression of the ramus, with a sharp postero-inferior ridge. The upper and lower canines are rather large but low. The male P₃is very wide, with well developed posterior crests; the P₄is rounded, with a large talonid and weak notches and clefts. Median lingual notches of the lower molars form an acute angle. Although our incomplete knowledge of T. atlanticus precludes a detailed phylogenetic analysis, we suggest that it arose by clado-genesis from the T. darti–T. oswaldi lineage; it is replaced by the latter species in the Pleistocene.Le gisement de Ahl al Oughlam près de Casablanca (Maroc), daté d'environ 2,5 Ma, a livré une belle collection deTheropithecus atlanticus (Thomas, 1884), espèce du Pliocène supérieur nord-africain qui n'était jusque là connue que par son holotype, une molaire inférieure d'Algérie. T. atlanticus, qui peut maintenant être bien mieux défini, se distingue bien des autres espèces du genre, dont la diversité est ainsi accrue. La mandibule de T. atlanticus est très caractéristique par son espace rétro-molaire vaste et profond, et sa dépression supra-latérale de la branche montante également très profonde, avec un rebord inférieur aigu. Les canines supérieures et inférieures sont grosses mais basses. La P₃mâle est très large, avec des crêtes postérieures très développées; la P₄est arrondie, avec un grand talonide et des sillons peu profonds. Sur les molaires inférieures, le débouché de la vallée médiane forme un angle aigu. Bien que notre connaissance imparfaite de T. atlanticus interdise une analyse phylétique détaillée, nous suggérons une dérivation par cladogenèse à partir de la lignée T. darti–T. oswaldi; cette dernière espèce le remplace au Pléistocène.     

Culture condition for production of glucoamylase from rice bran byAspergillus terreus

Summary Optimal conditions for the production of glucoamylase from rice bran usingAspergillus terreus in stationary culture were a medium containing 20 g rice bran/l, 0.3% (w/v) (NH₄)₂SO₄ and 0.2% (w/v) peptone at 30°C with an initial pH of 3.0. Enzymatic activity was maximal after 4 d. Glucose was the major reducing sugar produced by hydrolysis of starch. Carbohydrates favouring induction of glucoamylase were, in order: maltose, starch, cellobiose, lactose, glucose, fructose and galactose. Amino acids, in particular glycine, lysine, isoleucine and histidine, were vital for glucoamylase synthesis. Tween 80 and Triton X-100 enhanced the growth but suppressed glucoamylase synthesis.

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Conditions de culture pour la production de glucoamylase à partir de son de riz parAspergillus terreus

Résumé Les conditions optimales pour la production de glucoamylase à partir de son de riz en utilisantAspergillus terreus en culture en état stationnaire, consistent en un milieu contenant 20 g de son de riz par litre, 0.3 % (poids/vol.) de (NH₄)₂ SO₄ et 0.2 % (poids/vol.) de peptone, à 30 °C avec un pH initial de 3.0. L'activité enzymatique est maximum après 4 jours. Le glucose est le principal sucre réducteur produit par hydrolyse de l'amidon. Les hydrates de carbone qui favorisent l'induction de la glucoamylase, sont, dans l'ordre: le maltose, l'amidon, la cellobiose, le lactose, le glucose, le fructose et le galactose. Les acides aminés, en particulier la glycine, la lysine, l'isoleucine et l'histidine sont vitales pour la synthèse de glucoamylase. Le tween 80 et le triton X-100 augmentent la croissance mais suppriment la synthèse de glucoamylase.

     

Mesure in vivo de la radioactivite thyroïdienne apres injection d'iode radioactif 131I chez les colombides

Résumé La mesure précise in vivo de l'iode radioactif fixé par la thyroïde du Pigeon en fonction du temps après injection de ¹³¹I est délicate, en raison, d'une part, de la position anatomique de la thyroïde, d'autre part, de la masse des tissus juxtathyroïdiens, dont la radioactivité interfère avec celle de la glande.Nous avons conu un appareil de contention, qui, en immobilisant l'animal non anesthésié, permet de placer et de maintenir la glande dans une position identique par rapport au compteur, lors de chaque mesure.La radioactivité des tissus juxtathyroïdiens est évaluée à partir de celle d'une zone abdominale bien déterminée.La reproductibilité des mesures de radioactivité dans la zone thyroïdienne est comparable à celles d'autres méthodes d'étude in vivo chez les Mammifères. L'erreur effectuée sur la mesure de la radioactivité thyroïdienne, exprimée en % de la dose injectée, est en moyenne de 10%.     

Les Oppeliidae (Ammonitina) de l'horizon à Collotiformis (Callovien supérieur, zone à Athleta) de la région dijonnaise (Côte-d'Or, France)

In the Dijon area, the top of the Athleta zone contains rich ammonite fauna dominated quantitatively by two families: Perisphinctidae and Oppeliidae. The Oppeliidae are diversified and make up a numerically larger proportion of the ammonite fauna than in the underlying strata (up to 57 %). The exceptional state of preservation of the ammonites has permitted a precise study to be made of ontogenesis and intraspecific variability. Four sub-families are found (Oppeliinae, Hecticoceratinae, Distichoceratinae and Taramelliceratinae), within which sexual dimorphs have been recognised. One small form, characterized by lappets and a body chamber with ellipticoidal-trending coiling, is interpreted as the microconch dimorph of the Paralcidia genus which was unknown until now. One specimen of Creniceras, the oldest collected in Côte-d'Or, can be interpreted as the microconch dimorph of Taramelliceras.

Résumé

Dans la région dijonnaise, le sommet de la zone à Athleta renferme une riche faune ammonitique, quantitativement dominée par deux familles : Perisphinctidae et Oppeliidae. Par rapport aux niveaux sous-jacents, la famille des Oppeliidae est diversifiée et représente une part numériquement plus importante de la faune ammonitique (jusqu'à 57 %). L'excellente conservation des ammonites a autorisé une étude précise de l'ontogenèse et de la variabilité intraspécifique au sein de la famille. Quatre sous-familles sont représentées (Oppeliinae, Hecticoceratinae, Distichoceratinae et Taramelliceratinae), au sein desquelles les dimorphes sexuels ont été reconnus. Une petite forme, caractérisée par des apophyses jugales et une chambre d'habitation à enroulement à tendance ellipticoïde, est interprétée comme le dimorphe microconque, inconnu jusqu'à présent, du genre Paralcidia. Un spécimen de Creniceras, le plus ancien récolté en Côte-d'Or, pourrait correspondre au dimorphe microconque des Taramelliceras.     

Miocene Sanitheriidae (Suiformes, Mammalia) from Namibia and Kenya: systematic and phylogenetic implications

Sanitheres are enigmatic small suoids with bunoselenodont cheek teeth and a tendency for complication of the premolars by polycuspy and polycristy. Until a few years ago virtually nothing was known about their anterior dentition, but recent discoveries in Greece, Kenya and Namibia have thrown light on their incisor and canine morphology, and reveals among other things that the canines are highly sexually dimorphic, and the dm/1 is replaced by a p/1. Material from Kipsaraman, Kenya, collected between 1997 and 2003, consists of parts of mandibles and many isolated teeth, including elements of the deciduous dentition, a significant proportion of which are unworn. These new finds confirm the aberrant nature of the sanithere dentition within a suoid framework, and support their classification as a family separate from Suidae and Palaeochoeridae (= Old World Tayassuidae).

Résumé

Les sanithères sont de petits Suoïdes aux dents jugales bunosélénodontes avec des prémolaires qui présentent une tendance à la multiplication des cuspides et des crêtes (“polycuspidie” et la “polycristie”). Jusqu’à récemment, on ne connaissait rien sur la morphologie de leur dentition antérieure, mais des découvertes récentes réalisées en Grèce, au Kenya et en Namibie, lèvent le voile sur la morphologie de leurs incisives et de leur canine. Ainsi, il apparaît que les canines sont très dimorphes et que la dm/1 inférieure est remplacée par une p/1. Le matériel de Kipsaraman au Kenya, récolté entre 1997 et 2003, consiste en des fragments de mandibules et de nombreuses dents isolées, dont des dents déciduales, qui pour la plus grande part ne sont pas usées. Ces nouveaux fossiles confirment la nature aberrante de la dentition des sanithères au sein des Suoidea, et supporte leur classification dans une famille distincte des Suidae, et des Palaeochoeridae (= Tayassuidae de l’Ancien Monde).     

Purification and properties of a wheat leaf N-acetyl-β-d-hexosaminidase

An N-acetyl-β-d-hexosaminidase has been purified from primary wheat leaves (Triticum aestivum L.) by freeze-thawing, (NH₄)₂SO₄ precipitation, methanol precipitation, gel filtration, cation exchange chromatography and affinity chromatography on concanavalin A-Sepharose. The activity of the purified preparations could be stabilised by addition of Triton X-100 and the enzyme was stored at -20°C without significant loss of activity. The enzyme hydrolysed pNP-β-d-GlcNAc (optimum pH 5.2, K_m 0.29 mM, V_max 2.56 μkat mg⁻¹) and pNP-β-d-GalNAc (optimum pH 4.4, K_m 0.27 mM, V_max 2.50 μkat mg⁻¹). Five major isozymes were identified, with isoelectric points in the range 5.13–5.36. All five isozymes possessed both N-acety-β-d-glucosaminidase and N-acetyl-β-d-galactosaminidase activity. Inhibition studies and mixed substrate analysis suggested that both substrates are catalysed by the same active site. Both activities were inhibited by GlcNAc, 2-acetamido-2-deoxygluconolactone, GalNAc and the ions of mercury, silver and copper. The K_is for inhibition of N-acetyl-β-d-glucosaminidase activity were: GlcNAc (15.3 mM) and GalNAc (3.4mM). For inhibition of N-acety-β-d-galactosaminidase activity the corresponding values were: GlcNAc (18.2 mM) and GalNac (2.5 mM). The enzyme was considerably less active at releasing pNP from pNP-β-d-(GlcNAc)₂ and pNP-β-d-(GlcNAc)₃ than from pNP-β-d-GlcNAc. The ability of the N-acetyl-β-d-hexosaminidase to relase GlcNAc from chitin oligomers (GlcNAc)₂ (optimum pH 5.0) and (GlcNAc)₃₋₆ (optimum pH 4.4) was also low. Analysis of the reaction products revealed that the initial products from the hydrolysis of (GlcNAc)_n were predominantly (GlcNAc)_n−1 and GlcNAc.     

Synthesis and antitumor activity of new d-seco and d-homo androstane derivatives

Starting from 3β-hydroxy-17-oxo-16,17-secoandrost-5-ene-16-nitrile (1), the new 16,17-secoandrostane derivatives 4–9 were synthesized. On the other hand, 3β-hydroxy-17-oxa-d-homoandrost-5-ene-16-one (10) yielded the new d-homo derivatives 12, 13 and 15. In vitro antiproliferative activity of selected compounds against three tumor cell lines (human breast adenocarcinoma ER+, MCF-7, human breast adenocarcinoma ER−, MDA-MB-231, prostate cancer AR−, PC-3, and normal fetal lung fibroblasts, MRC-5) was evaluated. Compounds 3 and 12 showed strong antiproliferative activity against PC-3 cells, the IC₅₀ values being 2 μM and 0.55 μM, respectively. Compounds 6 (10 μM) and 14 (9 μM) showed moderate activity against MDA-MB-231 cells. The synthesized compounds 1–3, 5–8, 10 and 12–15 were not toxic to normal fetal lung fibroblasts cells, MRC-5.     

Four acetylcholinesterase genes in the nematode Caenorhabditis elegans

Whereas a single gene encodes acetylcholinesterase (AChE) in vertebrates and most insect species, four distinct genes have been cloned and characterized in the nematode Caenorhabditis elegans. We found that ace-1 (mapped to chromosome X) is prominently expressed in muscle cells whereas ace-2 (located on chromosome I) is mainly expressed in neurons. Ace-x and ace-y genes are located in close proximity on chromosome II where they are separated by only a few hundred base pairs. The role of these two genes is still unknown.

Résumé

À l'inverse de la situation des vertébrés et de la majorité des insectes, chez qui un gène unique code pour l'acétylcholinestérase (AChE), quatre gènes d'AChE ont été clones et caractérisés chez Caenorhabditis elegans. Le gène ace-1 (localisé sur le chromosome X) et le gène ace-2 (chromosome I) assurent respectivement l'expression de l'AChE dans les tissus musculaire (ace-1) et nerveux (ace-2). Les gènes ace-x et ace-y ne sont séparés que de quelques centaines de paires de bases sur le chromosome II et leur rôle est pour l'instant inconnu.     

The crystal and molecular structure of 1,6-anhydro-β-d-mannopyranose

The crystal structure of 1,6-anhydro-β-d-mannopyranose, C₆H₁₀O₅, is orthorhombic, P2₁2₁2₁, with a = 10.971(2), b = 13.935(3), c = 9.012(1) Å, V = 1377.76 »³ (MoKα, λ = 0.7107 Å), Z = 8, D_x = 1.563 M.gm⁻³, D_m = 1.565 M.gm⁻³. the structure was solved by MULTAN and refined to R(F) = 0.043 for 2355 reflections. The two symmetry-independent molecules in the unit cell have similar conformations, except for the orientation of one of the three hydroxyl groups. The conformation of the pyranose rings is ¹C₄ distorted towards E_o, and that of the anhydro rings is E. There are significant differences between the two molecules in two of the four C---O bond-lengths. These occur where there are important differences in the hydrogen-bonding environment of the oxygen atoms. The molecules are hydrogen-bonded by three linear and three bifurcated O---H···O interactions which form four-membered loops linked into infinite chains. Empirical force-field calculations with MMI-CARB reproduced the geometry of the molecules within the variations observed experimentally between the two molecules, except for a C---O bond in one of the molecules. The effect of excluding the anomeric effect from the theoretical calculations was not significant. Calculations for an intramolecularly hydrogen-bonded molecule were also carried out as a model for the molecules in a non-polar solvent.