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.

     

Etude par la R. M. N. de la germination de la Graine d’Avoine

The time-evolution of germination of oat seeds, suspended in the standard 5mm N. M. R. tube and supplied by water, was investigated continuouslyin vivo by the pulsed N. M. R. of water protons at the level of the seed. The results show that the spin- lattice relaxation time T1 yield the physiological information: in the germinated (living) seeds, the T¹’s are higher than in the killed seeds.      

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.     

Sur la fermentation de la glucose parCl. Tetani

Conclusion Selon nous nos recherches ne forment ni une confirmation ni une amplification de l'observation dePrévot etBoorsma, mais nous combattons les conclusions que ces auteurs ont tirées de leurs recherches. La souche 132 est impure sans parler de son origine. Il en suit que la faculté de cette souche de fermenter la glucose manque de toute force de démonstration à l'égard de la question posée. Conformément à la grande majorité des auteurs qui travaillent dans ce domaine nous sommes toujours d'avis que les souches tétaniques normales ne fermentent pas la glucose.      

Mr. de la Roche replies

Review of the literature reveals sporadic but true increases in the prevalence and death rates for asthma over the past 25 years. Although changes in hereditary, allergic and environmental factors must be considered as possible causes of this increase, its suddenness points to risk factors that change rapidly. Such is the case with atmospheric pollutants, notably nitrogen dioxide and particles, both of which have been shown to have adverse effects on the tracheobronchial tree. These pollutants tend to concentrate inside homes, especially since the early 1980s, when the energy crisis brought about changes in the home environment.     

Structures de la cabuamine et de la vincorine

Cabuamine is identified as O-methyl-hydrogeno akuammine.