Figure 4.

The cortisol-binding capacity of CBG in human serum is disrupted by purified LasB but not by protease IV. A, The cortisol-binding capacity of CBG in human serum was determined in 1 μl human serum after incubation with 1 μg purified LasB for 4 hours, 8 hours, or 16 hours at 37°C. A progressive decrease in cortisol-binding capacity was observed with approximately 50% remaining after 16 hours of incubation. Incubations were performed in triplicates. B, P. aeruginosa medium (P.aeru) was preincubated with 0.05 mM TLCK as an inhibitor of protease IV for 1 hour at 37°C, filtered and then incubated with human serum for 16 hours at 37°C (see Methods for details). The cortisol-binding capacity of CBG was not protected by TLCK, suggesting that protease IV is not involved in CBG cleavage. The data are presented as mean percentage ± SD of steroid-binding activity relative to a control that did not include P. aeruginosa media.