Abstract
The outer membrane of Gram-negative bacteria has two major types of solute permeation systems: the porin permeability channels, and molecule-specific facilitated diffusion channels (reviewed [ 11). We developed an in vitro assay method for determination of solute permeability through porin channels and h-receptor channels [2-51. Since this procedure only provides the end point of solute equilibrium, an in vitro assay method determining the rate of soIute permeability was desired. Here we report a new in vitro method for determination of membrane permeability by loading the intravesicular space of reconstituted vesicle membranes with purified enzyme and assaying substrate degradation inside the vesicles. The apparent permeability rates of various substances were determined by the vesicle membranes reconstituted from porin, A-receptor, or maltose-inducible outer membrane protein of Salmonella typhimurium (44 000 mol. wt (44 k) protein) [6]. The result suggested that this method might be applicable to in vitro determination of simple facilitated diffusion rates of various molecules through membranes.
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