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  • 1
    ISSN: 1432-1017
    Keywords: Rhodopsin ; Metarhodopsin II ; Opsin ; Transient conformational changes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Arguments are presented which support the possibility that the unfolding of the rhodopsin molecule during photolysis up to the stage of metarhodopsin II is followed by a spontaneous refolding of the protein, once the isomerized retinaldehyde has left its original binding site. Such a transient conformational change might imply a very similar conformation for rhodopsin and opsin, apart from the presence of the chromophore.
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  • 2
    ISSN: 1432-119X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The permeability of the pancreatic epithelium to horseradish peroxidase is investigated in the resting and carbachol stimulated rabbit pancreas. Horse radish peroxidase administered to the bathing medium of the isolated rabbit pancreas appears in the secreted fluid of the pancreas in a relatively low concentration. Carbachol stimulates both protein secretion and the passage of horse radish peroxidase into the secretory fluid. Histochemical assessment shows that horseradish peroxidase enters the interstitial spaces of the pancreatic tissue and is present along basal and lateral plasma membranes of acinar and ductular cells. In the absence of carbachol, horseradish peroxidase is seen more frequently in the tight junctions of ductular cells than in those of acinar cells. However, in the carbachol stimulated gland horseradish peroxidase is observed in the junctions between adjacent acinar cells more frequently than in the unstimulated gland. Freeze-fracture of acinar cells shows that the number of tight junctional strands and the tight junction depth are slightly decreased upon carbachol stimulation. The findings suggest that cholinergic stimulation of the exocrine pancreas increases the permeability of the acinar cell junctions to moderately large molecules such as horseradish peroxidase. This may result in an increase of the concentration of the molecule in the secreted fluid.
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  • 3
    ISSN: 1432-0827
    Keywords: Pyrophosphatase ; Teeth ; pH ; Cations ; Cofactors ; EDTA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé 1. La présence de pyrophosphatase inorganique (PPi-ase), à pH optimum de 8.7, a pu être mise en évidence au niveau des molaires de hamsters, âgés de 3 jours. L'activité se situe dans la fraction qui précipite. 2. Aucune activité en PPi-ase acide n'est observée dans le surnageant ou la fraction qui précipite. 3. Zn2+, et possiblement le Co2+, semblent agir comme co-facteur pour l'activité de la PPi-ase. Mg2+ augmente l'activité en PPi-ase, car Mg-PP i 2− est sans doute le vrai substrat de l'enzyme.
    Abstract: Zusammenfassung 1. Die Anwesenheit von anorganischer Pyrophosphatase (PPi-ase) mit einem pH-Optimum von 8.7 konnte in den Molaren von 3 Tage alten Hamstern gezeigt werden; das Enzym wurde vorwiegend in der ausfällbaren Fraktion gefunden. 2. Weder im Überstand noch in der ausfällbaren Fraktion konnte eine signifikante saure PPi-ase-Aktivität nachgewiesen werden. 3. Zn2+ und möglich Co2+ scheinen als Cofaktoren für die PPi-ase-Aktivität zu wirken; diese wird durch Mg2+ erhöht, vermutlich weil Mg-PP i 2− das eigentliche Substrat für das Enzym ist.
    Notes: Abstract 1. The presence of an inorganic pyrophosphatase (PPi-ase) with a pH optimum of 8.7, could be demonstrated in the molars of 3-day old hamsters, where it was primarily located in the sedimentable fraction. 2. No significant acid PPi-ase activity could be detected either in the supernatant or in the sedimentable fraction. 3. Zn2+, and possibly Co2+, appears to act as a cofactor for the PPi-ase activity; Mg2+ increases the PPi-ase activity, probably because Mg-PP i 2− is the true substrate for the enzyme.
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  • 4
    ISSN: 1432-0827
    Keywords: Pyrophosphatase ; Teeth ; Diphosphonates ; Cofactors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé 1. L'effet de trois diphosphonates, de l'ethane-1-hydroxy 1.1, diphosphonate (EHDP), de méthane-diphosphonate (MDP) et de dichlorométhane diphosphonate (Cl2MDP) sur l'activité en pyrophosphatase alcaline inorganique a été étudié au niveau des molaires de hamsters. 2. L'inhibition des trois diphosphonates parait surtout liée à leur complexation par un cation bivalent qui n'est pas le Mg2+ et qui agit comme un co-facteur pour l'enzyme. 3. Pour le diphosphonate EHDP, l'inhibition est provoquée partiellement, en outre, par l'antagonisme entre MgPP i 2− et MgEHDP2−.
    Abstract: Zusammenfassung 1. Der Einfluß von 3 Diphosphonaten, nämlich Aethan-1-hydroxy-1,1-Diphosphonate (EHDP), Methandiphosphonat (MDP) und Dichloromethandiphosphonat (Cl2MDP) auf die Aktivität der anorganischen alkalischen Pyrophosphatase in Hamstermolaren wurde untersucht. 2. Die Hemmung durch die 3 Diphosphonate scheint vor allem auf ihre Komplexierung mit einem bivalenten Kation zurückzuführen zu sein, welches nicht Mg2+ ist und als Cofaktor für das Enzym wirkt. 3. Beim EHDP wird die Hemmung zudem teilweise durch eine Kompetition zwischen MgPP i 2− und MgEHDP2− hervorgerufen.
    Notes: Abstract 1. The influence of three diphosphonates, ethane-1-hydroxy 1.1 diphosphonate (EHDP), methane-diphosphonate (MDP) and dichloromethane diphosphonate (Cl2MDP) on the inorganic alkaline pyrophosphatase activity in hamster molars has been investigated. All three diphosphonates inhibit the enzyme activity. 2. The inhibition by the three diphosphonates appears to be primarily due to their complexation with a bivalent cation which is not Mg2+, and which acts as a cofactor for the enzyme. 3. For the diphosphonate EHDP, the inhibition is, moreover, in part due to a competition between MgPP 1 2− and MgEHDP2−.
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  • 5
    ISSN: 1432-0827
    Keywords: Phosphatase ; Inorganic ; Pyrophosphatase ; Teeth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé 1. Certaines propriétés de la pyrophosphatase inorganique et de la phosphatase alcaline sont décrites dans les molaires de hamsters de trois jours. 2. Le pH optimum pour la pyrophosphatase inorganique (PPi-ase) est de 8,7 et, pour la phosphatase alcaline (p-NPP-ase), il est 10,3. 3. Le rapport Mg2+: PPi pour l'activité pyrophosphatasique optimale est de 1∶1. On ne trouve pas de rapport optimal pour la p-NPP-ase. 4. Le rapport entre l'activité enzymatique de la partie liée à la membrane et la partie soluble est de 3,4∶1 (S.E. 0,37) pour la PPi-ase et de 3,2∶1 (S.E. 0,42) pour l'activité de la p-NPP-ase. 5. Une compétition réciproque des substrats pour la pyrophosphatase, et la phosphatase alcaline a pu être mise en évidence. 6. Les deux activités enzymatiques ont les mêmes courbes d'activité de température avec le même maximum de température de 38°C. 7. La microdissection d'améloblastes et de cellules du stratum intermédium, realisée à partir de coupes lyophilisées, montre le même rapport pour les deux activités enzymatiques: Stratum intermédium: améloblastes pour la PPi-ase 4,7 (S.E. 0,93) et pour la p-NPP-ase 4.2 (S.E. 0.79). 8. l'Electrophorese à haute tension (free-flowing) donna une distribution, comparable de p-NPP-ase et de PPi-ase, qui fut largement différente de la distribution de proteine. 9. Il semble donc que les deux activités soient dues à la même enzyme.
    Abstract: Zusammenfassung 1. Es werden einige Eigenschaften der in den Backenzähnen 3 Tage alter Hamster vorliegenden anorganischen Pyrophosphatase (PPi-ase) und alkalischen Phosphatase (p-NPP-ase) beschrieben. 2. Das optimale pH liegt für die PPi-ase bei 8,7 für die p-NPP-ase bei 10,3. 3. Das Verhältnis von Mg2+ zu PPi für die optimale PPi-ase-Aktivität ist 1∶1. Für die p-NPP-ase besteht kein eindeutiges optimales Verhältnis. 4. Das Verhältnis der Enzymaktivität des membrangebundenen zum löslichen Anteil ist 3,4∶1 (S.E. 0,37) für die PPi-ase-Aktivität und 3,2∶1 (S.E. 0,42) für die p-NPP-ase-Aktivität. 5. Eine gegenseitige Substratkompetition zwischen der PPi-ase- und der p-NPP-ase-Aktivität wird gezeigt. 6. Die Aktivitätskurven bei verschiedenen Temperaturen sind für beide Enzymaktivitäten gleich und haben ihr Maximum bei 38°C. 7. Schnitte von Ameloblasten und von Zellen aus dem Stratum intermedium aus lyophilisiertem Material zeigten das gleiche Aktivitätsverhältnis für beide Enzymaktivitäten: Stratum intermedium zu Ameloblasten für PPi-ase 4,7 (S.E. 0,93) und für p-NPP-ase 4,2 (S.E. 0,79). 8. Free-flowing Hochspannungselektrophorese des Homogenates ergab gleiche Verteilung für p-NPP-ase und PPi-ase, die sich von der Proteinverteilung deutlich unterschied. 9. Daraus wird geschlossen, daß die beiden Aktivitäten zu ein und demselben Enzym gehören.
    Notes: Abstract 1. Some properties of inorganic pyrophosphatase (PPi-ase) and alkaline phosphatase (p-NPP-ase) in the molars of 3-day-old hamsters are described. 2. The pH optimum for inorganic pyrophosphatase is 8.7, for alkaline phosphatase 10.3. 3. The ratio of Mg2+: PPi for optimal inorganic pyrophosphatase activity is 1∶1. There is no clear optimal ratio in the case of p-NPP-ase. 4. The ratio of the enzymic activity of the membrane bound fraction to the soluble fraction is 3.4∶1 (S.E. 0.37) for PPi-ase and 3.2∶1 (S.E. 0.42) for p-NPP-ase activity. 5. A mutual substrate competition for the pyrophosphatase and alkaline phosphatase activities is demonstrated. 6. Both enzymatic activities have similar temperature-activity curves with the same maximum at 38°. 7. Microdissection of ameloblasts and stratum intermedium cells from lyophilized sections showed the same activity ratio for both enzyme activities: Stratum intermedium: ameloblasts for PPi-ase 4.7 (S. E. 0.93) and for p-NPP-ase 4.2 (S.E. 0.79). 8. High-voltage, free-flowing electrophoresis of the homogenate gave equal distribution patterns for p-NPP-ase and PPi-ase greatly different from the protein distribution pattern. 9. It is concluded that the two activities are due to the same enzyme.
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 227 (1970), S. 1259-1260 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The first value for the molar absorbance of cattle rhodopsin was reported by Wald and Brown3. They illuminated a rhodopsin sample of known absorbance in the presence of hydroxylamine to obtain quantitatively the all-trans retinaldehyde in the form of its oxime. Having determined the molar ...
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  • 7
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 222 (1969), S. 879-881 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Various unsatisfactory explanations for this discrepancy have been advanced: involvement of sulphydryl groups2-6, formation of a carbonium ion on one of the polyene carbons7-9 and changes in the charge of the N atom in the Schiff base link by nearby substituents10. Other workers, initially Morton ...
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  • 8
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Analytical chemistry 28 (1956), S. 2035-2036 
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
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  • 9
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] We have recently shown that the molar ratio of the a and b subunits in the enzyme from the rabbit kidney is 1:1 (ref. 11). We have also determined the molecular weights of the subunits by sedimentation equilibrium analysis in the absence of detergent. After correction for carbohydrate and residual ...
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