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1985 (1)
1974 (1)
1Author    WolfgangF. Osswald, Sigrid Zieboll, E. F. ElstnerRequires cookie*
 Title    Comparison of pH Changes and Elicitor Induced Production of Glyceollin Isomers in Soybean Cotyledons  
 Abstract    During the incubation of soybean cotyledons with Pmg-elicitor for 22 hours the pH of the diffusion droplets increases from 7.2 to 8.3. This pH-shift is a precondition for the formation of the typical red colour of the diffusion droplet. After inhibiting the pH-shift by the use of 100 mM phosphate or Tris buffer instead of 10 mM buffer as solvent for the elicitor, the red colour is no longer formed with the exeption of 100 mM Ammediol buffer. However, the normal pattern of pterocarpan induction can be measured in the absence of the red colour in the diffusion droplet. Tris and Ammediol buffers exhibited a smaller pterocarpan induction as compared to phosphate buffer as solvent for the Pmg-elicitor. 
  Reference    Z. Naturforsch. 40c, 477—481 (1985); received April 22 1985 
  Published    1985 
  Keywords    pH Changes, Elicitor, Glyceollin Isomers, Soybean Cotyledons 
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 TEI-XML for    default:Reihe_C/40/ZNC-1985-40c-0477.pdf 
 Identifier    ZNC-1985-40c-0477 
 Volume    40 
2Author    HinderkM. Emrich, Roland ReichRequires cookie*
 Title    Über Primärreaktionen beim Sehvorgang Thermodynamischer und kinetischer Einfluß des pH-Wertes auf die M etarhodopsin-I-II-Umwandlung Protonenverbrauch als Auswirkung einer Konform ationsänderung Prim ary Reactions in the Visual Process Thermodynamic and Kinetic Influence of pH on the M etarhodopsin I-II Transition Proton Consumption as an Effect of a Conformation Change  
 Abstract    In isolated bovine rod outer segments metarhodopsin I —II absorption-changes are measured using rapid flash-photometry. The rapid H f-uptake accompanying this transition is measured using phthaleine pH-indicators. 1. The meta I —II equilibrium is pH-dependent in the same manner as the proton uptake (Figs 1 ,1 4). This can be explained by the assumption that the meta II conformation is stabilized by the protonization of an amino-group, which in its protonized state cannot be re-enfolded into the hydrophobic core of the molecule, since it is too polar (Fig. 15). In the proposed model the con­ formation-regulating proton binding group is not in the chromophoric region of rhodopsin. This resolves the well known contradiction between the expected bathochromic and observed hypso-chromic shift of meta II H+. The model furthermore involves that the dissociation-constant of the protonized group differs from the measured apparent pK = 6.3. 2. The meta I —II transition is H+ (and OH")-catalysed (Figs 4, 5). The kinetics show usually a characteristic deviation from a first-order process (Fig. 2). This can be explained by some in­ homogeneity of the rhodopsin-molecules e. g. some differences in the shieldings of the catalytic centers from H+ (and OH-). 3. The activation energy decreases with increasing proton-concentration (Fig. 6). The protons seem to open a new reaction pathway with a smaller activation energy. 4. Triton X 100 and ethanol increase, sodium-desoxycholate slows down the velocity of the M-I-II-transition, whereas digitonin has only a small effect (Fig. 7). 5. The relaxation-velocity of the optical pH-signal depends on the structural state of the rhodopsin-containing substrate (Figs 10. 11). The outer membrane of the outer segment and the disc-membrane are regarded as possible H+-diffusion-barriers (Fig. 12), because the time lag between Mu-signal and pH-signal is nearly eliminated, when the membranes are destroyed by digitonin. 6. In some experiments, using successive non-saturating flashes, an initial H+-uptake of 2 — 3 H+/M n was observed (Fig. 17). After full-bleaching, how'ever, the ^ H +/^M ii-ratio is one. The hypothesis of a conformative coupling of 2 — 3 rhodopsin-molecules is presented (Fig. 18). The possible existence of an "unfolded" state of rhodopsin is discussed on the basis of a photo-regeneration-experiment, in which no H+-release was observed (Figs 19, 20). 
  Reference    (Z. Naturforsch. 29c, 577 [1974]; eingegangen am 2. Mai/6. Juni 1974) 
  Published    1974 
  Keywords    Rhodopsin-photolysis, Photoreception, pH-Change, Proton-catalysis, Conformation-change 
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 TEI-XML for    default:Reihe_C/29/ZNC-1974-29c-0577.pdf 
 Identifier    ZNC-1974-29c-0577 
 Volume    29