Cellular internalisation uptake

For undersaturated ([M] < Km) systems with relatively fast internalisation kinetics (kmt > k, ), the uptake of trace metals may be limited by their adsorption. Because the transfer of metal across the biological membrane is often quite slow, adsorption limitation would be predicted to occur for strong surface ligands (small values of k ) with a corresponding value of Km (cf. equations (35) and (36)) that imposes an upper limit on the ambient concentration of the metal that can be present in order to avoid saturation of the surface ligands. More importantly, as pointed out by Hudson and Morel [7], this condition also imposes a lower limit on the carrier concentration. Since the complexation rate is proportional to the metal concentration and the total number of carriers, for very low ambient metal concentrations, a large number of carriers are required if cellular requirements are to be satisfied. 

With respect to cellular uptake (Fig. 4.15, top), the nature of the chromophorc and its attachment mode to the macrocycle primarily determine the localisation and the kinetics of the cell internalisation, but not the charge of the complex or its lipophiUcity. The reason invoked is that polycyclic sensitiser units are recognised by protein association. Therefore, the nature of the substituent on the sensitiser units is a key parameter for protein affinity [147]. 

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