FIG. 4.

TNS fluorescent analysis of TcsL. The analysis of pH-induced conformational changes in TcsL was carried out with the fluorescent probe TNS. Each spectrum represents the experimental sample with background (TNS and buffer alone) subtracted. For the pH shift condition, the toxin was treated with TNS at pH 7.5. The solution was then titrated to pH 4.0 by gradual addition of 1 N HCl and returned to neutrality by addition of 1 N NaOH. (A) TcsL hydrophobicity across a range of pHs. TcsL was incubated with TNS at pHs 4.0, 5.0, 6.0, 7.0, and 8.0, and the fluorescent spectrum of each sample was obtained. TNS fluorescence for samples above pH 5.0 were not above background levels. Emission from pHs 6.0, 7.0, and 8.0 were not detectable above background levels. (B) TNS analysis of TcsL hydrophobicity following pH shift.