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'pH Dependence' in keywords Facet   section ZfN Section C  [X]
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1996 (1)
1981 (1)
1974 (1)
1Author    H. Stieve, T. MalinowskaRequires cookie*
 Title    The pH Dependence of the Receptor Potential of the Hermit Crab Photoreceptor  
 Abstract    The pH dependence of the receptor potential (ReP) of isolated layers of photoreceptor cells from the hermit crab compound eye (Eupagurus bernhardus L.) was determined. Measurements were performed, using extracellular electrodes, in the range pH 3.5 — 9.5 in three different buffer systems: Tris, glycine, and phosphate. The amplitude of the ReP was highest at pH 7.5 and decreased in more acidic and more alka­ line salines (Fig. 4). Relative to the changes in ReP amplitude, the changes in time course and shape of ReP were small. Salines of pH other than 7.5 caused an increase of the latent period but decreased the peak amplitude time and the repolarizing phase (i2). Alkaline salines caused about the same changes in the ReP as acidic salines. The only observed difference was that repolarisation was more strongly influenced by alkaline solutions and that the plateau magnitude was depressed relatively more than the peak magnitude in acidic environments. Of the three buffers used, Tris had the weakest influence on the ReP and phosphate buffer the strongest. In contrast to the good reproducibility of the experimental results, the reversibility of the pH effects was generally poor; the effects with glycine-buffer were more reversible than those with Tris. 
  Reference    (Z. Naturforsch. 29c, 147 [1974]; received December 19 1973) 
  Published    1974 
  Keywords    Receptor Potential, pH Dependence, Buffer Type, Photoreceptor Cell, Crustacea 
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 TEI-XML for    default:Reihe_C/29/ZNC-1974-29c-0147.pdf 
 Identifier    ZNC-1974-29c-0147 
 Volume    29 
2Author    N. G. Faleev3, S. N. Spirina3, V. S. Ivoilov3, T. V. Dem, R. S. Phillips0Requires cookie*
 Title    The Catalytic Mechanism of Tyrosine Phenol-Lyase from Erwinia herbicola: The Effect of Substrate Structure on pH-Dependence of Kinetic Parameters in the Reactions with Ring-Substituted Tyrosines  
 Abstract    Apparently hom ogeneous tyrosine phenol-lyase (TPL) from Erwinia herbicola has been prepared by a new method. The pH -dependencies o f the main kinetic parameters for the reactions of Erwinia TPL with tyrosine, 2-fluorotyrosine, 3-fluorotyrosine, 2-chlorotyrosine, and 3.4-dihydroxyphenylalanine (D O P A) have been studied. The pattern of pH-dependence ° f V^max depends on the nature of the substituent in the aromatic ring. For the substrates bearing small substituents (H, 2-F, 3-F) Kmax values were found to be pH-independent. For 2-chlorotyrosine and DO PA Vmax decreased at lower pH, the effect being described by equa­ tion with one pKa. Generally two bases are reflected in the pH dependence of Vmax/K m. The first base, probably is responsible for the abstraction of a-proton, while the second one, interacts with the phenolic hydroxyl at the stage of binding. The reaction of TPL with DOPA differs from the reactions with other tyrosines by the requirement of an additional base which is reflected in the pH-profiles of both and VmaJ K m. For the reaction of TPL from Citrobacter intermedins with DO PA only Vma J K m values could be determined. The activity of Citrobacter enzyme towards DO PA is considerably less than that of E. herbicola enzyme, and its maximal value is attained at higher pH. 
  Reference    Z. Naturforsch. 51c, 363 (1996); received N ovem ber 22 1995/February 27 1996 
  Published    1996 
  Keywords    Tyrosine Phenol-Lyase, Mechanism, Kinetics, Substrate Structure, pH -Dependence 
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 TEI-XML for    default:Reihe_C/51/ZNC-1996-51c-0363.pdf 
 Identifier    ZNC-1996-51c-0363 
 Volume    51 
3Author    Rainer Jaenicke, Hans-Dietrich Liidemann, Gerhard SchmidRequires cookie*
 Title    Pressure, Temperature and pH Dependence of the Absorption Spectrum of Reduced Nicotinamide Adenine Dinucleotide  
 Abstract    Enzymological studies at high hydrostatic pressure generally involve temperature, pH and pressure as variables, owing to the effect of adiabatic compression and the ionization volume o f the buffer system. In the case of N AD dependent oxidoreductases this implies that the extinction coefficient o f the coenzyme may be affected by p, T and pH, apart from the spectral change accompanying the redox reaction. Measurements o f the pressure dependence of the absorbance of N AD H show a slight red shift and a 1% decrease (3% increase) o f the absorbance at 339 nm (360 nm) at 2 kbar. The pH depen­ dence at the given wavelengths amounts to —(2.4 ± 0.1)% per pH unit (25 °C), while the intrinsic temperature effect (after correction for thermal expansion) is o f the order o f -0.2% per degree (2 0 -3 0 °C). Applying buffers with negligible ionization volume, 366 nm is the optimum wavelength for high pressure studies up to 2 kbar because here the pressure dependent spectral changes o f the N ADH absorption vanish. 
  Reference    Z. Naturforsch. 36c, 84—8 (1981); received October 9 1980 
  Published    1981 
  Keywords    Absorption, Dehydrogenases, High Pressure, NADH, Oxidoreductases, pH Dependence, Tem­ perature Dependence 
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 TEI-XML for    default:Reihe_C/36/ZNC-1981-36c-0084.pdf 
 Identifier    ZNC-1981-36c-0084 
 Volume    36