Beweis für die Beteiligung von beweglichen Transportstrukturen (Trägern) beim Ionentransport durch pflanzliche Membranen und die Kinetik des Anionentransports bei Elodea im Licht und Dunkeln

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Abstract
Influx and efflux of anions in leaves of Elodea canadensis were investigated. A major component of phosphate efflux was found to be a function of the external phosphate concentration in accord with saturation kinetics, i.e. it was found to be proportional to phosphate influx. This suggests that the transport structures which mediate ion transport in plant membranes are mobile and can work in both directions (Fig. 7C). The higher the external concentration the more bound ions (A b − , Fig. 7C) are exchanged for external ions (A a − ) instead of being transported back to the inside of the membrane. Thus it was demonstrated that ion transport in plants is mediated by carriers or transportases. The action of the carriers is supported by ATP or another “energy-rich” compound which is regenerated by ATP; ATP may be supplied by the mitochondria or/and chloroplasts. In line with these findings some transport phenomena exhibited features of coenzyme kinetics. Magnitude and molecular nature of the carrier motion are unknown. There is no evidence for rotating or shuttling monovalent carriers. The carriers may be polyvalent and may be part of bigger structural units within the membrane. Nevertheless, these experimental observations are rather consistent with the idea that plant membranes contain tertiary or quarternary formed proteins or lipoproteins than with the conventional lipid bilayer models of cell membranes. Licht (Erhöhung des ATP-Spiegels) steigert die relative Transportgeschwindigkeit aller untersuchten Transportsysteme, nicht dagegen die maximale Transportgeschwindigkeit mancher Systeme. Der Efflux einer Ionenspecies ist bei höherer Außenkonzentration desselben Ions eine Funktion der Außenkonzentration. Dies beweist die Existenz von beweglichen Transportstrukturen (Carriern) in pflanzlichen Zellmembranen. Der metabolische Ionentransport durch pflanzliche Membranen kann somit aus zwei Komponenten bestehend betrachtet werden: 1. Energieabhängige Umorientierung von spezifischen Bindungsstellen von einer Membranseite zur anderen (metabolische Komponente). 2. Ionenaustausch an den spezifischen Bindungsstellen (physikalische Komponente).