Characterization of the transferrin-iron uptake system in Neisseria meningitidis

The transferrin-iron uptake system of six Neisseria meningitidis strains was characterized using 125I-transferrin in receptor assays and 55Fe-loaded transferrin in uptake assays. Receptors for transferrin varied among the strains both in number (from 700 to 4700 receptors per cell) and in their affinity constants for the protein (Ka ranged from 0.7 x 10(7) to 4.0 x 10(7) l mol-1). Neither receptor numbers nor affinity constants were significantly different in carrier and invasive strains, although the Ka seem to be somewhat higher in the latter. Iron uptake from transferrin was also variable among the strains, but showed the same lack of correlation with their origin.