Quantitative analysis of pump-mediated fluxes in reconstituted lipid vesicles

Abstract

Reconstituted vesicles with built-in ion pumps (or other transport proteins) are usually heterogeneous with respect to size and with respect to the number of pump molecules present in the membrane. In this paper a method is described for the analysis of ion flux experiments with reconstituted vesicles which is based on the statistical properties of the vesicle population. The method is based on the assumption that the fraction of vesicles containing n = 0, 1, 2,… pump molecules is given by a Poisson distribution; it further requires an estimate of the width of the distribution of vesicle radii. Under favourable conditions the intrinsic turnover rate of the pump and the density of functional pump molecules in the vesicle membrane can be determined separately. The method can be applied to isotope-flux experiments, to optimal measurements of active ion transport and to studies of pump-mediated charge transport.