Characterization of gastric ATPase vesicle transport

The microsomal fraction of both dog and hog gastric mucosa contains a K⁺ activated ATPase. ATP phosphorylates a peptide of c̅ 100,000 Mᵣ in both species, and dephosphorylation is stimulated by K⁺. By a combination of differential and zonal density gradient centrifugation a membrane fraction is produced containing almost exclusively this peptide region. These vesicles, upon the addition of ATP, take up H⁺ and extrude K⁺. The action of ionophores such as nigericin or valinomycin and the uptake of lipid permeable anions such as thiocyanate or anilino-naphthosulfonic acid indicate the lack of a potential difference during transport. Reconstitution of this material into a planar bilayer indicates that ATP activates a K⁺ conductance and hence, in the presence of K⁺ also a low potential difference is observed. These data suggest that this H⁺ pump is non-electrogenic as prepared in the vesicular form. Using an antibody obtained from rabbits immunized with the highly purified membrane fractions, it was demonstrated that this membrane was derived uniquely from gastric parietal cells. Hence, based on the ability of this ATPase to actively transport H⁺, its cellular origin and on the well known K⁺ requirement for acid secretion in amphibia and mammals, it is concluded that this ATPase is a component of the HCl secretory mechanism of gastric mucosa.Paper I Secretion by in Vitro Amphibian Gastric Mucosa. IN: Physiology of Gastric Secretion: NATO Institute, Myren, J., ed, p. 186 -202, Oslo Press, 1968. • Paper II Frog Gastric Mucosal ATPase. Proc. Soc. Exptl. Biol. Med. 119: 1023 -1027, 1965. • Paper III Action of SCN on Rat Liver Mitochondria. Proc. Soc. Exptl. Biol. Med. 133: 456 -459, 1970. • Paper IV Action of Thiocyanate on Gastric Mucosa in Vitro. Biochim. Biophys. Acta 173: 509 -517, 1969. • Paper V Role of ATP and ATPase in Gastric Acid Secretion. IN: Gastric Secretion, (Sachs, G., Heinz, E., Ullrich, K.J., eds), Academic Press, New York, pp. 321 -343, 1972. • Paper VI Properties of ATPase of Gastric Mucosa. V. Preparation of membranes and mitochondria by zonal centrifugation. Biochim. Biophys. Acta 311: 545 -564, 1973. • Paper VII Characterization of Gastric Mucosal Membranes. VI. The presence of channel- forming substances. Biochim. Biophys. Acta 332: 233 -247, 1974. • Paper VIII Characterization of Gastric Mucosal Membranes. Composition of gastric cell membranes and poly - peptide fractionation using ionic and nonionic detergents. Arch. Biochem. Biophys. 161: 456 -471, 1974. • Paper IX Pronase Method for Isolation of Viable Cells From Necturus Gastric Mucosa. Gastroenterology 61: 189 -200, 1971. • Paper X Specific Effect of Acetylsalicylic Acid on Cation Transport of Isolated Gastric Mucosal Cells. Am. J. Physiol. 235: E16 -E21, 1978. • Paper XI Studies on Adenyl Cyclase in Necturus Gastric Mucosa. Arch. Biochem. Biophys. 143: 123 -126, 1971. • Paper XII Adenyl and Guanyl Cyclase in Rabbit Gastric Mucosa. Am. J. Physiol. 225: 1359 -1363, 1973. • Paper XIII Action of Cholinergic Drugs on Necturus Gastric Mucosa. Am. J. Physiol. 210: 1056 -1060, 1970. • Paper XIV Action of Burimamide, a Histamine Antagonist, on Acid Secretion in Vitro. Am. J. Physiol. 226: 898- 902, 1974. • Paper XV Effects of Sodium Removal on Acid Secretion by the Frog Gastric Mucosa. Proc. Soc. Exptl. Biol. Med. 123: 47 -52, 1966. • Paper XVI Ion Transport by Amphibian Antrum in Vitro. I. General Characteristics. Am. J. Physiol. 228: 1188 -1198, 1975. • Paper XVII Quantitation of Conductance Pathways in Antral Gastric Mucosa. J. Gen. Physiology 65: 645 -662, 1975. Paper XVIII Properties of Gastric Antrum. III. Selectivity and modification of shunt conductance. Gastroenterology 72: 72 -77, 1977. • Paper XIX A Molecular Approach to Epithelial Conductance: Gastric Mucosa. Aired Benzon Symp. V. Transport Mechanisms in Epithelia, Munksgaard, Copenhagen, pp. 257 -274, 1973. • Paper XX Conductance Pathways in Epithelial Tissues. Exp. Eye Res. 16: 241 -249, 1973. • Paper XXI Electrical Properties of Isolated Cells of Necturus Gastric Mucosa. Biochim. Biophys. Acta 241: 261 -272, 1971. • Paper XXII Microelectrode Studies of Gastric Mucosa and Isolated Gastric Cells. Symp. Med. Hoechst. IN: Electrophysiology of Epithelial Cells, p. 257 -279, 1971. • Paper XXIII Microelectrode Studies of Fundic Gastric Mucosa: Cellular Coupling and Shunt Conductance. J. Membr. Biol. 19: 105 -128, 1974, • Paper XXIV The Action of Amytal on Frog Gastric Mucosa. Biochim. Biophys. Acta 143: 522 -531, 1967. Paper XXV Metabolism of Dog Gastric Mucosa. I. Nucleotide Levels in Parietal Cells. J. Biol. Chem. 250: 8321 -8329, 1975. • Paper XXVI Metabolism of Dog Gastric Mucosa. Levels of glycolytic citric acid cycle and other intermediates. J. Biol. Chem. 252: 8572 -8581, 1977. • Paper XXVII Redox Involvement in Acid Secretion in the Amphibian Gastric Mucosa. J. Membr. Biol. 35: 189 -204, 1977. • Paper XXVIII REVIEW: H⁺ Transport by a Non-electrogenic Gastric ATPase as a Model for Acid Secretion. Rev. Physiol. Biochem. Pharmac. 79: 133 -167, 1977. • Paper XXIX Characterization of Gastric Mucosal Membranes. VIII. Localization of peptides by iodination and phosphorylation. J. Biol. Chem. 250: 4802 -2809, 1975. • Paper XXX Characterization of Gastric Mucosal Membranes. IX. Fractionation and Purification of K⁺- ATPase containing vesicles by zonal centrifugation and free flow electrophoresis technique. Biochim. Biophys. Acta. 465: 311 -330, 1977. • Paper XXXI A Non -electrogenic H⁺ Pump in Plasma Membranes of Hog Stomach. J. Biol. Chem. 251: 7690 -7698, 1976. • Paper XXXII Proton Transport by Gastric Membrane Vesicles. Biochim. Biophys. Acta 464: 313 -327, 1977. • Paper XXXIII Cation Transport by Gastric H⁺ + K⁺ ATPase. J. Membr. Biol. 32: 361 -381, 1977. • Paper XXXIV Use of l-anilino-8-naphthalene sulfonate as a Probe of Gastric Vesicle Transport. J. Membr. Biol. 32: 301 -318, 1977. • Paper XXXV Reconstitution of a Proton Pump from Gastric Mucosa. J. Membr. Biol. 35: 285 -301, 1977. • Paper XXXVI Metabolic and Membrane Aspects of Gastric H⁺ Transport. Gastroenterology 73: 931 -940, 1977. • Paper XXXVII Tissue and Cell Localization of Hog Gastric Plasma Membrane by Antibody Technique. Proc. Symp. Gastric. Ion Transport, Special Suppl. Acta Physiol. Scand (Obrink, K.J. and Flemstrom,-G., eds) p. 293 -305, 1978. • Paper XXXVIII Transport Parameters of Gastric Vesicles. Proc. Symp. Gastric Ion Transport, Special Suppl. Acta Physiol. Scand. (Obrink, K.J. and Flemstrom, G., eds) p. 409 -426, 1978. • Paper XL Enzymic Modification of Gastric Transport ATPase. IN: Frontiers of Biological Energetics (Dutton, P.L., Leigh, J., Scarpa, A., eds) Academic Press, New York, Vol. 1, p. 545 -554, 1978. • Paper XLI Transport Characteristics of Frog Gastric Membranes Biochim. Biophys. Acta 551: 432 -447, 1979. • Paper XLII Quantitation of Hydrogen Ion and Potential Gradients in Gastric Plasma Membrane Vesicles. Biochemistry 17: 3345 -3353, 1978

pH-dependent gating mechanism of the Helicobacter pylori urea channel revealed by cryo-EM.

The urea channel of Helicobacter pylori (HpUreI) is an ideal drug target for preventing gastric cancer but incomplete understanding of its gating mechanism has hampered development of inhibitors for the eradication of H. pylori. Here, we present the cryo-EM structures of HpUreI in closed and open conformations, both at a resolution of 2.7 Å. Our hexameric structures of this small membrane protein (~21 kDa/protomer) resolve its periplasmic loops and carboxyl terminus that close and open the channel, and define a gating mechanism that is pH dependent and requires cooperativity between protomers in the hexamer. Gating is further associated with well-resolved changes in the channel-lining residues that modify the shape and length of the urea pore. Site-specific mutations in the periplasmic domain and urea pore identified key residues important for channel function. Drugs blocking the urea pore based on our structures should lead to a new strategy for H. pylori eradication

Structure of the proton-gated urea channel from the gastric pathogen Helicobacter pylori.

Half the world's population is chronically infected with Helicobacter pylori, causing gastritis, gastric ulcers and an increased incidence of gastric adenocarcinoma. Its proton-gated inner-membrane urea channel, HpUreI, is essential for survival in the acidic environment of the stomach. The channel is closed at neutral pH and opens at acidic pH to allow the rapid access of urea to cytoplasmic urease. Urease produces NH(3) and CO(2), neutralizing entering protons and thus buffering the periplasm to a pH of roughly 6.1 even in gastric juice at a pH below 2.0. Here we report the structure of HpUreI, revealing six protomers assembled in a hexameric ring surrounding a central bilayer plug of ordered lipids. Each protomer encloses a channel formed by a twisted bundle of six transmembrane helices. The bundle defines a previously unobserved fold comprising a two-helix hairpin motif repeated three times around the central axis of the channel, without the inverted repeat of mammalian-type urea transporters. Both the channel and the protomer interface contain residues conserved in the AmiS/UreI superfamily, suggesting the preservation of channel architecture and oligomeric state in this superfamily. Predominantly aromatic or aliphatic side chains line the entire channel and define two consecutive constriction sites in the middle of the channel. Mutation of Trp 153 in the cytoplasmic constriction site to Ala or Phe decreases the selectivity for urea in comparison with thiourea, suggesting that solute interaction with Trp 153 contributes specificity. The previously unobserved hexameric channel structure described here provides a new model for the permeation of urea and other small amide solutes in prokaryotes and archaea

Werkstoffbewertung und Konstruktionsanforderung : Festvortrag anläßlich der Gauß-Gedenkfeier in Braunschweig am 30. April 1957

The design of a construction in a new material is a very difficult task, because of the complexities of design requirements, on the one hand, and the peculiar properties of most high strength materials, on the other hand. It is now practically impossible to integrate the three different types of endeavor which lead to a successful design, namely the experimental procurement of design data and laws, their mathematical evaluation, and the utilization of these efforts by the designer. Therefore, a great need exists for specific experimentation aimed at establishing the material behavior under conditions incorporating one or several service variables. Examples of such work, combining service and laboratory tests, are described, which relate to different design efforts, namely: the simulation of service conditions for super-high strength steels by means of the notch tension test; the surface rolling of steel and magnesium and the specific conditions to be maintained, hereby, in order to arrive at maximum strength. The calculation of the service life of turbine buckets, based on stress rupture tests. Modell tests with lead and other low melting metals to arrive at the load-carrying capacity, as well as at forging conditions, for high melting metals

Unitary evolution of perturbations of a two-dimensional black hole

We discuss massive scalar perturbations of a two-dimensional dilaton black hole. We employ a Pauli-Villars reqularization scheme to calculate the effect of the scalar perturbation on the Bekenstein-Hawking entropy. By concentrating on the dynamics of the scalar field near the horizon, we argue that quantum effects alter the effective potential. We calculate the two-point function explicitly and show that it exhibits Poincare recurrences.Comment: 11 page

Do Development Economists Matter?

SUMMARY If appropriate policies, rather than initial economic conditions, have produced successful development, why are appropriate policies not more widely adopted by developing country governments — or, why has the advice of most development economists not been heeded? The ‘new (neoclassical) political economy’ offers a systematic explanation of why policy?makers behave as they do. Instead of assuming that governments are agencies for promoting the public interest, the new political economy's models endogenise the policy?maker in states characterised variously as predatory (‘the Leviathan state’), as factional, or as bureaucratic. The limitations of these models are addressed, and their relevance to developing countries is questioned. A more eclectic approach to political economy is, therefore, suggested, in which older elements are combined with the new. Such an approach is then applied to the political economy of trade policy. RESUME Les économistes spécialisés dans le domaine du développement sont?ils importants? Si des mesures appropriées, plutôt que des conditions économiques initiales ont produit un développement qui a eu du succès, pourquoi des mesures adéquates ne sont?elles pas adoptées plus largement par les gouvernements des pays en voie de développement. — ou pourquoi le besoin de l'assistance de la plupart des economistes spécialisés dans les problèmes de développement ne s'est?elle pas fait sentir? La nouvelle politique économique (néo?classique) offre une explication systématique expliquant pourquoi ceux qui prennent les décisions se comportent comme ils le font. Au lieu d'assumer que les gouvernements sont des agences pour la promotion de l'intérêt publique, les nouveaux modèles d'économie politique endogénisent ceux qui prennent les décisions, les charactêrisant de prédateurs (‘l’état du Leviathan'), de fonctionel, ou de bureaucratique. Les limitations de ces modèles sont adressés, et leur pertinence concernant les pays en voie de développement sont mis en question. Une approche plus ecclectique à l'economie politique est donc, suggérée, dans laquelle des éléments plus anciens sont associés avec les nouveaux. Une telle approche est ensuite appliquée à l'économie politique du commerce. RESUMEN ¿Importan los economistas del desarrollo? Si el desarrollo exitoso ha sido producido más bien por políticas adecuadas que por condiciones económicas iniciales ¿por qué aquellas no son más ampliamente adoptadas por los gobiernos de los países en desarrollo o por qué no ha sido escuchado el consejo de muchos economistas del desarollo? La “nueva política económica (neoclásica)” ofrece una explicación sistemática del comportamiento de los diseñadores de política. En lugar de suponer que los gobiernos son agencias para promover el interés público, los nuevos modelos de economía política endogenizan el diseño de política en estados caracterizados como predatorios (“el estado Leviathan”), faccionales o burocráticos. Se consideran las limitaciones de estos modelos y se cuestiona su relevancia para los países en desarrollo. En consecuencia, se sugiere un enfoque más ecléctico que combina elementos antiguos con los nuevos aplicándose luego tal enfoque a la política comercial