Figure 2.

Liposome swelling assay. Liposomes (18-μl aliquots) were diluted into 0.6 ml of an isoosmotic solution containing the indicated solute, and initial rates of decrease at OD₄₀₀ were determined. (A) Swelling rates of PapC proteoliposomes with l-arabinose as the solute. The swelling rate is directly proportional to the amount of PapC incorporated into the liposomes. (B) LPS stimulates the swelling activity of PapC-containing proteoliposomes. LPS (0–5 nmol) was reconstituted along with 0 (•) or 10 (▴) μg of PapC into liposomes and swelling rates were measured with l-arabinose as the solute. (C) Swelling rates in the presence of various molecular weight solutes. Swelling rates of proteoliposomes reconstituted with 20–36 μg of PapC (•), 10 μg of PapC plus 1.0–2.5 nmol of LPS (▴), or 0.5 μg of isolated OM (□) were determined in the presence of l-arabinose (150 Da), d-galactose (180 Da), N-acetyl-d-glucosamine (221 Da), sucrose (342 Da), or d-raffinose (504 Da). Rates were plotted as the percent of the arabinose swelling rate for each proteoliposome preparation.