La ouate comme source de facteur de croissance de microorganisme.

Sans résumé     

Controle de la chaine de biosynthese de la threonine chezE. coli

Resume Le travail décrit dans cet article s'appuie sur la théorie du contrôle du métabolisme et a pour but la mesure des coefficients de contrôle des différentes étapes sur le flux de production de thréonine. Le coefficient de contrôle d'une étape sur un flux mesure quantitativement la réponse du flux aux variations de l'étape. Cette notion est donc particulièrement importante aussi bien dans les situations pathologiques (diminution de l'activité d'une étape) qu'en biotechnologies où au contraire les étapes sont amplifiées.La mesure des coefficients de contrôle des étapes d'une chaîne métabolique permet donc de connaître celle(s) dont l'amplification doit entraîner une augmentation concomitante du flux.Nous avons appliqué ces concepts à l'étude de la voie de biosynthèse de la thréonine à partir de l'aspartate.La voie de la biosynthèse de la thréonine à partir de l'aspartate est constituée de cinq étapes catalysées par cinq activités enzymatiques: l'aspartokinase (AK), l'aspartate semi-aldéhyde déshydrogénase (ASA-DH), l'homosérine déshydrogénase (HDH), l'homosérine kinase (HK) et la thréonine synthase (TS).La mesure du coefficient de contrôle de la première étape (AK, insensible à la rétro-inhibition par la thréonine dans la souche étudiée) a montré qu'elle était faiblement contrôlante. L'étude a révélé la présence d'une inhibition jusqu'alors inconnue de l'homosérine kinase par la lysine.Un début de modélisation de cette chaîne de biosynthèse permet d'expliquer les résultats expérimentaux.

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This paper deals with the application of the metabolic control theory, especially the measurement of control coefficients, to the threonine pathway inE. coli. The control coefficient of a step on a metabolic flux quantitatively assesses the flux response to the step variations. This concept is particularly relevant both in pathological situations (decrease in the activity of an enzymatic step in the metabolism) and in biotechnologies, where, on the contrary steps are amplified.Measurement of the control coefficients of the steps of a metabolic network makes it possible to know those whose amplification should lead to a simultaneous increase in the fluxes.We have applied these concepts to threonine biosynthesis from aspartate inE. coli. The threonine pathway starting from aspartate involves five steps catalyzed by five enzyme activities: aspartokinase (AK), aspartate-semialdehyde-dehydrogenase (ASA-DH), homoserine dehydrogenase (HDH), homoserine kinase (HK) and hreonine synthetase activity (TS).Measurement of the control coefficient of the first step (AK, insensitive to threonine inhibition in the studied strain) has shown that it controls threonine production weakly. Our study has revealed a hitherto unknown inhibition of homoserine kinase activity by lysine.Mathematical modeling of this metabolic pathway has been undertaken to better understand our experimental results.

     

Estimation de l'agressivite de differents isolats de fusarium oxysporum f. sp. lycopersici (schlecht) sn. et h.

The author intends to compare, as precisely as possible, the respective agressiveness of several strains of Fusarium osysporum f. sp. lycopersici with regards to varying susceptibility among several varieties of tomatoes.The criteria used to estimate the pathogenicity of a strain is the decrease in growth which occurs in the epicotyl part of infected plantlets.The importance of the differences between the groups of plants is discussed.     

Hybrides de Cobayes sauvages et de cobayes domestiques.

Ohne Zusammenfassung     

Influence de l'oxygene sur les transferts d'electrons de la photosynthese. I. Influence de diverses concentrations d'oxygene sur quel ques reactions de Hill

Influence of oxygen on the electron transfers of photosynthesis. I. Influence of some oxygen concentrations on some Hill reactions

The influence of O₂ concentrations on the Hill reactions in the presence of p-benzoquinone, ferricyanide, NADP⁺, NADP⁺ plus ferredoxin has been studied with isolated spinach chloroplasts.

Because of the partial reoxidation of the hydroquinone, which is depending upon the O₂ concentration, it does not seem possible to localize a site of action for O₂.

With ferricyanide the influence of O₂ is weak. However, the rate of ferricyanide reduction is increased in the presence of O₂. The observed stimulation is greater for 21% O₂ than for 70% O₂. Bicarbonate stimulates the ferricyanide reduction and decreases the stimulating effect of 21% O₂.

O₂ decreases the rate of NADP⁺ reduction. Ferredoxin as well as bicarbonate stimulate the NADP⁺ reduction and reduce the O₂ inhibition.

These results seem to indicate that O₂ may enter the electron transport chain at a site situated near Photosystem I and before the ferredoxin's site.

The inhibitory effect of O₂ on the Hill reactions with p-benzoquinone and NADP⁺ is depending upon the plants' growth conditions. It is greater with plants grown under weak light.     

Cestodes d'oiseaux de Côte-d'Ivoire. II. Parasites de Coraciiformes et Piciformes

Résumé Les cestodes récoltés en Côte d'Ivoire chez deux ordres d'oiseaux, les Coraciiformes et les Piciformes, sont présentés. Un nouveau genre, Thaumasiolepis (Hymenolepididae, Hymenolepidinae), est créé et discuté. Il comprend des cestodes récoltés chez différentes espèces de Capitonidae et caractérisés par des crochets rostraux spiniformes tout à fait originaux. L'espèce T. microarmata est créée pour ce matériel. D'autre part deux nouveaux Raillietina de Picidae, R. (S.) campetherae et R. (P.) yapoensis sont décrits. R. (S.) campetherae est la première espèce de ce sous genre trouvée chez les Piciformes. Biuterina meropina macrancistrota est trouvé chez Merops albicollis. Ce taxon est élevé au rang d'espèce et devient par conséquent B. macrancistrota Fuhrmann, 1908. Skrjabinoporus merops (Woodland, 1928) Spassky & Borgarenko, 1960 est retrouvé. Cette espèce peu commune est redécrite et sa position parmi les Metadilepididae confirmée. Enfin, Raillietina cf (P.) bargetzii Mahon, 1954 est signalé chez Gymnobucco calvus.

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Cestodes collected in the two bird orders, the Coraciiformes and the Piciformes, in the Ivory Coast are presented. The new genus Thaumasiolepis (Hymenolepididae, Hymenolepidinae) is created and discussed. It includes cestodes collected in two species of the Capitonidae. Its main characteristic is the presence of very unusual spiniform hooks. The species T. microarmata is created for this material. We also describe two new species of Raillietina parasitising the Picidae, R. (P.) yapoensis and R. (S.) campetherae, the latter being the first species of this subgenus recorded from the Piciformes. In addition, Biuterina meropina macrancistrota has been found in Merops albicollis. We recognize a full specific status for this taxon which becomes B. macrancistrota Fuhrmann, 1908. Skrjabinoporus merops (Woodland, 1928) Spassky & Borgarenko, 1960 has been rediscovered. This rare species is redescribed and its position among the Metadilepididae is confirmed. Finally, Raillietina cf (P.) bargetzii Mahon, 1954 is recorded from Gymnobucco calvus.

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Ce travail fait partie de la thèse du premier auteur.     

La laparotomie dans la maladie de Hodgkin: signification de l'atteinte de la rate.

We retrospectively reviewed 224 cases of Hodgkin''s disease, in 120 of which staging laparotomy was performed. The surgical findings in cases of clinical stage I or II disease with supradiaphragmatic presentation or clinical stage III disease did not influence the treatment plans. Of the 64 patients with positive results of laparotomy (splenic or lymph node involvement or both) 51 had splenic involvement; their 5-year survival rate, 57%, was similar to that of the patients with clinical or pathological stage III disease - 58% and 54% respectively. At laparotomy 11 patients with pathological stage III disease were found to have isolated splenic involvement; their 5-year survival rate, 64%, was not appreciably different from that of the patients with clinical stage II disease, 70%; both groups were treated with radiotherapy only. From this study we can conclude that splenic involvement in Hodgkin''s disease has no deleterious effect on survival and that splenic irradiation seems to be as effective as splenectomy in controlling the disease.