FIG. 7.

Pore-forming function of native MOMP. (A) Example of proteoliposome swelling data. Proteoliposomes containing 20 μg of native MoPn MOMP were prepared as described in Materials and Methods, and a portion of the suspension was diluted in isotonic solutions of either a tetrasaccharide, stachyose (lower curve), or a pentose, l-arabinose (upper curves). The time-dependent swelling (and the consequent decrease in scattering or optical density) is evident in the l-arabinose solution (three consecutive traces are shown), whereas in stachyose (terminated early), very little changes in optical density occurred. The absolute values of optical density are lower in stachyose because of the higher refractive index of the isotonic stachyose solution. OD400, optical density at 400 nm. (B) Dependence of swelling rates on the amount of MOMP used in reconstitution. Proteoliposomes were reconstituted with different amounts of native MOMP, and the swelling rates in l-arabinose solution were measured. (C) Dependence of swelling rate on the size of solutes. Swelling was measured in isotonic solutions of l-arabinose, d-glucose, N-acetyl-d-glucosamine, and sucrose, with proteoliposomes reconstituted with native MoPn MOMP. Data obtained in three experiments are shown (▪, ▴, and ♦). For comparison, P. aeruginosa OprF porin was used in reconstitution in the same experiment (×). Data reported for the E. coli OmpF porin (41) are also included (•).