Fig. (4) Cyanolyzable sulfur of PspE1 and PspE2. Immediately following elution from the cation exchange column, fractions containing PspE1 (■) and PspE2 (▲) were adjusted to pH 7.0 by addition of 1 M Tris-HCl (pH 8.0). Aliquots were then treated with 100 mM cyanide for 5 min at room temperature. Thiocyanate was quantified as the ferric thiocyanate complex as described for the rhodanese assay. The amount of PspE was estimated using the Bradford protein assay [50], with bovine serum albumin as standard.