Argovithyris nov. gen. ET A. Birmensdorfensis (Brachiopoda) des couches a spongiaires de l'oxfordien moyen du Jura

The «Couches de Birmensdorf give, in Argovie (Switzerland) as in southern FrenchJura, a small Terebratulid: T. birmensdorfensisMoesch for which a new genus is defined: Argovithyris nov. gen. because it cannot be assigned to genus Loboidothyris.     

Gastric (H,K)-ATPase

Gastric acid secretion results from the activity of a specific ATPase, the (H+,K+)-ATPase. This enzyme, discovered in 1973, exchanges H+ for K+. It has two ATP binding sites, both involved in enzyme activity, whose affinities vary as a function of the H+ and K+ concentrations. Hydrolysis of ATP at the highest affinity site leads to the synthesis of a covalent aspartyl phosphate which accumulates in the absence of K+. The presence of this cation accelerates dephosphorylation resulting in the stimulation of ATPase (and PNPPase) activity. The structure of membranous (H+,K+)-ATPase is poorly defined. n-Octylglucoside solubilizes an active enzyme of 390-420 kDa which can be partly depolymerized using cholate. The monomer, characterized in SDS has a 95 kDa molecular mass and is inactive. In the presence of magnesium, (H+,K+)-ATPase catalyzes the active and neutral exchange of H+ for K+ at the expense of ATP. In the absence of ATP, (H+,K+)-ATPase acts as a passive transporter exchanging K+ for K+ at maximal rate and H+ for K+ at a 20 times slower rate.     

One-Electron Reduction of Daunorubicin Intercalated in DNA or in A Protein : A Radiolysis Study

The one-electron reduction of daunorubicin, an anthracycline antibiotic, intercalated in DNA or in the apoprotein of the riboflavin binding protein, was studied by y radiolysis. The two reduction mechanisms appear very similar to the one found for the non-intercalated drug. Hydrogen peroxide, which oxidizes non-intercalated hydroquinone daunorubicin with two electrons in one step (C. Houee-Levin, M. Gardes-Albert and C. Ferradin, FEBS lett. 173 27-30, (1984), reacts with daunorubicin hydroquinone in DNA but not in the protein. It appears thus that the site accessibility to hydrogen peroxide in DNA is better than in the protein. Biological consquences are discussed.     

Nouveaux repères biostratigraphiques à terebratulidés (Brachiopodes) dans le Tithonien inférieur ouest-européen

The discovery of a new species of Terebratulid (Xestosina sera nov. sp.) in the Lower Tithonian allows to specify the biostratigraphical subdivision of the Gigas Zone. This also allows to improve the correlations, when ammonites are lacking, among the Tithonian deposits of Aquitaine, the northern Jura and the eastern border of the Paris Basin. The critical revision of the Xestosina genus gives a nomenclatural setting argued to the index-species of biozones. It constitutes a brachiopods based parallel scale for the Kimmeridgian and Tithonian Stages.     

Association of the quinate : NAD+ oxidoreductase with one dehydroquinate hydro-lyase isoenzyme in corn seedlings

A quinate : NAD⁺ oxidoreductase has been purified from cornseedlings. This enzyme co-migrates with a dehydroquinate hydro-lyaseisoenzyme whatever separation technic is used. This is strongevidence that the two activities are associated in an enzymecomplex or in a bifunctional enzyme, in addition to the previouslycharacterized association of the shikimate : NADP⁺ oxidoreductaseand another dehydroquinate hydro-lyase isoenzyme. The purifiedquinate : NAD⁺ oxidoreductase has a poor affinity for quinicacid and is only active in the presence of NAD⁺. The associateddehydroquinate hydro-lyase isoenzyme is strongly activated invitro by shikimic acid in a pH-dependent process. The possible role of this new association is discussed in thelight of previous results from alicyclic metabolism studiesin plants and microorganisms. (Received July 18, 1980; )     

Diversity of H2/CO2-Utilizing Acetogenic Bacteria from Fecesof Non-Methane-Producing Humans

The purpose of this work was to study H₂/CO₂-utilizing acetogenic population in the colons of non-methane-producing individuals harboring low numbers of methanogenic archaea. Among the 50 H₂-consuming acetogenic strains isolated from four fecal samples and an in vitro semi-continuous culture enrichment, with H₂/CO₂ as sole energy source, 20 were chosen for further studies. All isolates were Gram-positive strict anaerobes. Different morphological types were identified, providing evidence of generic diversity. All acetogenic strains characterized used H₂/CO₂ to form acetate as the sole metabolite, following the stoichiometric equation of reductive acetogenesis. These bacteria were also able to use a variety of organic compounds for growth. The major end product of glucose fermentation was acetate, except for strains of cocci that mainly produced lactate. Yeast extract was not necessary, but was stimulatory for growth and acetogenesis from H₂/CO₂. Received: 28 December 1995 / Accepted: 30 January 1996