Figure 4.

Relative accessibility of hydrophobic residues in Solfolobus solfataricus wild type (wt) amidase (A) and its Y41C mutant (B) monitored by the extrinsic fluorescence of 8-anilinonaphtalene-1-sulfonic acid ammonium salt (ANS). The ANS (25 µM) was added to the protein (2.5 µM), which had previously been incubated overnight at pH 8.0 (20 mM sodium phosphate, solid line) and at pH 5.0 (20 mM sodium citrate, dotted line). Fluorescence emission spectra (390 nm) were recorded at 20 °C, 10 min after the addition of ANS.