Thermodynamics of ouabain binding to human erythrocytes

A previous study reported that the uptake and release kinetics of ouabain by human erythrocytes in suspension could well be explained by a physical model which involves the slow Langmuir binding of the drug to the erythrocyte membrane. The purpose of the present investigation was to assess quantitatively the thermodynamics of this drug-membrane receptor interaction in order to evaluate the consistency of these parameters with the proposed kinetics model.Cellular drug uptake and release experiments were conducted at 20, 30 and 40°C, and the Langmuir adsorption and desorption rate constants as well as the Langmuir adsorption isotherms determined from the rate data. With the knowledge of these Langmuir parameters, it was possible to estimate the magnitude of all relevant thermodynamic properties by the use of established physicochemical theories.The activation energies and entropies for the ouabain adsorption and desorption processes were computed as 105 kJ/mol, 231 J/K per mol, 180 kJ/mol and 245 J/K per mol, respectively. The kinetic and isosteric heats of adsorption were found to be ?75.0 and ?72.4 kJ/mol, respectively. These findings suggest that the ouabain-erythrocyte membrane interaction represents a case of activated chemisorption which follows the Langmuir isotherm, thus, further underscoring the appropriateness of the Langmuir binding kinetics model.     

Genetic fine structure of the pyrE region containing the genes for ribosomal proteins L28 and L33 in Escherichia coli

Summary Temperature-sensitive mutants harbouring alterations in ribosomal proteins L28 and L33 have been isolated and used in mapping the genes coding for the two proteins. It was found that they mapped very close to each other and near pyrE at 80.7 min on the E. coli genetic map. The genes affected by the mutations have been concluded to be the structural genes for proteins L28 (rpmB) and L33 (rpmG) by constructing merodiploids heterozygous for pyrE and for the two ribosomal proteins. Various transduction studies with P1kc phages indicate the gene order in this region to be (rpmB, rpmG)-pyrE-spoT-gltC.     

The initiation of chromosome replication in a dnaAts46 and a dnaA+ strain at various temperatures

Summary The regulation of chromosome replication initiation was studied at various temperatures with an E. coli dnaA46 strain and its dnaA ⁺ parent. We find that, in both strains, the initiation mass varies depending upon growth temperature while the replication time remains constant relative to the cell doubling time. In the permissive temperature range, the initiation mass of the dnaA46 mutant strain is larger by a constant factor than that for a dnaA ⁺ strain. We conclude that, even at temperatures permissive for growth of the dnaA46 strain, the activity of the dnaA46 product is lower than that of the wild-type protein. The dnaA gene product, therefore, plays an important role in regulating initiation.     

Analysis of bromine-oxidised dextran by 13C-n.m.r. spectroscopy

Dextran T 10, elaborated by Leuconostoc mesenteroides NRRL B-512, was oxidised with aqueous bromine at pH 7.0. The resulting oxodextran and its methoximated derivative were analysed by ¹³C-n.m.r. spectroscopy. The total amount of keto groups and their positions were established. Assignments of the ¹³C signals were made by referring to spectra of the corresponding methyl glucosiduloses and an oxodextran having most of the carbonyl groups at position 3 of the glycopyranosyl residues. In accordance with the mechanism for bromine oxidation of mono- and di-saccharides, the glucopyranosyl residues of dextran were oxidised mainly at C-2 and C-4. Over-oxidation resulted in a small proportion of acidic, ring-cleavage products.     

An impregnation technique for studying distribution of mitochondria in central nervous system

Summary An impregnation technique for demonstration of mitochondria in central nervous system has been described. Formol perfused material is being chromated, embedded in paraffin and impregnated with a modified Nauta's method. The reaction is specific since reduced silver particles are deposed within the matrix of mitochondria. Phenomenon of complete and incomplete impregnation is discussed. Mitochondria in perikarya of neurons, dendrites and glia tend to be unstained if the impregnation is incomplete, while axonic and praesynaptic ones are labelled. In neuropil of different regions of the brain various types of mitochondrial aggregates appear in complete impregnation. The method may be a valuable tool for studying brain architecture and synaptology.With a grant of Alexander von Humboldt-Stiftung at the II. Institute of Anatomy, Berlin.     

Fettsäuregehalte in Lichtkulturen von Rhodospirillum rubrum während der Thylakoidmorphogenese

Zusammenfassung Der Zusammenhang zwischen der Ausbildung des intracytoplasmatischen Membransystems und dem Gehalt der Zellen an Fettsäuren und Lipid-Phosphor wird an Rhodospirillum rubrum untersucht. Trotz Steigerung des Membrangehaltes nach der Überführung aerober thylakoidfreier Dunkelzellen in anaerobe Lichtbedingungen bleibt der Gehalt an Fettsäuren und Lipid-Phosphor pro Gesamtzellprotein unverändert. Das gleiche Resultat ergibt sich, wenn eine Steigerung des Thylakoidgehaltes im System anaerob Normallicht (4000 Lux) anaerob Schwachlicht (400 Lux) hervorgerufen wird. Dieses Resultat eines konstanten Fettsäurespiegels wird nicht durch eine Änderung des Bezugsystems Protein erzielt. Der Quotient Proteingehalt pro Volumen dichtgepackter Bakterien bleibt während der Membransynthese konstant. Aus Licht- und Dunkelzellen werden eine Rohmembranund eine Rohzellwandfraktion angereichert. Die Wandfraktion aus aeroben Dunkelzellen enthält einen höheren Anteil der Gesamtfettsäuren der Zelle als die Wandfraktion aus anaeroben Lichtzellen. (2-¹⁴C)-Acetat wird von wachsenden Zellen unter Normallichtbedingungen (4000 Lux) in hoher Rate eingebaut. Nach der Umschaltung auf Schwachlicht (400 Lux) wird diese Aufnahme zugleich mit dem Wachstum gestoppt. Werden aerobe Dunkelzellen in semiaerobe Lichtbedingungen über-führt, wird der Gehalt an Fettsäuren und Lipid-Phosphor um 70% erhöht. Die Ergebnisse werden im Rahmen der Hypothese diskutiert, daß ein großer Teil der Zellfettsäuren in der Wand lokalisiert ist und daß dieser Anteil koordiniert mit dem Membrangehalt verändert werden kann.

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Contents of fatty acids in light cultures of Rhodospirillun rubrum during the synthesis of thylakoids

Summary The correlation between the formation of the intracytoplasmic membrane system and the content of fatty acids and lipid phosphorus in cells of Rhodospirillum rubrum is investigated. After induction of thylakoid synthesis by transferring aerobic dark grown cells into anaerobic light conditions, the content of fatty acids and lipid phosphorus per protein of the cells remains unchanged. The same result is found if the increase of thylakoid content is induced by lowering the light intensity from moderate (4000 lux) to low (400 lux) light intensity under anaerobic conditions. The constant level of lipids during the morphogenesis of thylakoids is not conditioned by a change of the protein content of the cells. The ratio protein to volume unit of wet packed bacteria is not changed during the synthesis of thylakoids. Crude cell wall and membrane fractions are isolated from light and dark grown cells. The wall fraction from dark aerobic grown cells contains more fatty acids than that of anaerobic light grown cells. Label from (2-¹⁴C)-acetate is rapidly incorporated by growing cells cultivated under moderate light intensity. After transfer to low light conditions acetate incorporation and growth stop immediately. If aerobic dark grown cells are transferred to semiaerobic light conditions the content of fatty acids and lipid phosphorus in the cells is increased by 70%. The results are discussed from the view that a great part of the fatty acids of the cells is localized in the cell wall and that this amount can be altered in coordination with the membrane content of the cells.

     

Book reviews

Ohne Zusammenfassung

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Book reviews

     

Ultrastruktur des Pseudoculus vonEosentomon (Protura,Insecta)

Zusammenfassung In der Feinstruktur unterscheidet sich der Pseudoculus vonEosentomon nicht wesentlich von dem der Acerentomiden. Durch einen Endokutikulaporus treten die dendritischen Fortsätze zweier Sinneszellen, jeweils umgeben von einer Hüllzelle, in den Außenraum des Pseudoculus ein. Der Außenraum wird nach distal von einer äußeren Kutikulaschicht — vermutlich Epikutikula — abgeschlossen. Sie vermittelt durch regelmäßig angeordnete lange Spalten die Verbindung zur Außenwelt. Am Grunde der Spalten finden sich Porentubuli, die mit den Hüllzellen oder den distalen Fortsätzen der Dendriten Kontakt haben können. Aus der Feinstruktur kann geschlossen werden, daß der Pseudoculus als Chemo-, Hygro- und/oder Thermorezeptor fungiert.

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Ultrastructure of the pseudoculus ofEosentomon (Protura, Insecta)

Summary Concerning its fine structure the pseudoculus of Eosentomon is quite similar to that of Acerentomide Protura. There are two sensory cells innervating the organ. From each of them one dendritic process derives, surrounded by one enveloping cell. The processes of these four cells enter the distal cavity of the pseudoculus through a pore in the endocuticular layer. The cuticular layer of the cap seems to consist of epicuticle only. It is furrowed by long clefts connecting the distal cavity of the organ with the outside. Poretubules insert at the base of the clefts and may have contact with the cell membranes of both enveloping cells and dendritic processes. According to its structure the pseudoculus may function as chemo-, hygro- and/or thermoreceptor.

Für technische Mitarbeit danke ich Frau G. Raabe, für die Anfertigung der Zeichnung Frau C. St. Friedemann.     

Beitrag zur Kenntnis der Sinnesorgane von Symphylen (Myriapoda)

Zusammenfassung Das Tömösvárysche Organ von Scutigerella immaculata wurde elektronenmikroskopisch untersucht. Es liegt in einer Epidermisinvagination direkt hinter der Basis der Antenne. Die Grube des Organs ist mit Kutikula ausgekleidet und steht durch eine rundliche Öffnung mit der Außenwelt in Verbindung. Zwei Drittel des Grubenraumes sind angefüllt mit einem Gitterwerk kutikulärer Stäbe, die distale Fortsätze von Sinneszellen enthalten. Unterhalb der Grube liegen mehrere Sinneszellen. Jede Sinneszelle formt proximal und distal einen schmäleren Fortsatz. Jeder distale Fortsatz läuft in zwei Zilienstrukturen aus, die unter Verzweigung in das Gitterwerk eintreten und sich auch dort weiter verzweigen. Die Sinneszellen werden von drüsigen Hüllzellen umfaßt. An ihnen können trichogene und tormogene Zellen unterschieden werden. Das Sekret der Hüllzellen umgibt die distalen Fortsätze der Sinneszellen von den Zilienstrukturen an bis in das Gitterwerk hinein. Die Kutikula des Gitterwerkes ist sehr dünn und von winzigen Poren durchsetzt.Nach einem Vergleich mit Sinnesorganen von Insekten muß vermutet werden, daß es sich beim Tömösváryschen Organ um ein Geruchssinnesorgan handelt, das vielleicht auch als Hygrorezeptor fungiert.

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Sense organs of symphyla (Myriapoda)II. Ultrastructure of the temporal organ of Scutigerella immaculata Newport

Summary The temporal organ of Scutigerella immaculata is situated in a pit just behind of the antenna. The pit represents an epidermal invagination. It is coated by cuticle and corresponds to the outside by a circular opening. More than half of the pit is filled up with a complicated network of branching and anastomosing cuticular protuberances. The cuticle of the protuberances is very thin and perforated by tiny pores. There are about ten sense cells situated under the pit, each of which forms a distal as well as a proximal process. Each distal process shows two ciliary structures. After branching they enter the cuticular protuberances and branch inside of it, as well. The sense cells are surrounded by glandular sheath cells, in which trichogen and tormogen cells can be distinguished. The secretion product of the sheath cells surrounds the distal parts of the sense cells inside of the cuticular protuberances. By comparison to sense organs of insects it must be presumed that the temporal organ represents an olfactory organ which may also function as hygroreceptor.

Ich danke Herrn Rau (Zentralinstitut für Elektronenmikroskopie der Technischen Universität Berlin) für die Durchführung der Arbeiten am Raster-Elektronenmikroskop und Frau Friedemann für die Anfertigung der Zeichnung.