Effects of pH and of Temperature on Saturable Transport Processes
In their molecular nature, specific membrane transport processes resemble enzyme reactions taking place in a continuous phase: They involve binding of a “substrate” molecule to a specific receptor site, the translocation proper corresponding to the substrate → product conversion, and dissociation of the “product”, in the transport case simply release of the bound molecule or ion to another aqueous phase, separated from the starting aqueous phase by the membrane. The amount of evidence supporting the above sequence of events is vast and need not be reiterated here. Kinetically, all such transports are characterized by a half-saturation constant which is formally identical with the Michaelis constant of enzyme kinetics and is a similarly complicated function of various rate constants comprised in the mechanism, and by a maximum rate of transport, involving the total amount of carrier protein present in a given amount of cells and a combination of first-order rate constants, again depending on the complexity of the system under consideration.
KeywordsYeast Species Transport Reaction Rhodotorula Glutinis Electrochemical Potential Gradient Histidine Imidazolium
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