Figure 1.

Titrations of zinc-reconstituted (A) and cadmium-reconstituted (B) α-domain (■) and β-domain (□) vs. pH. The absorbance change at 220 (or 250 nm) was obtained by subtracting the absorbance of the apoproteins at pH < 2 from those of the zinc or cadmium proteins at different pH values. Measurements were made on solutions containing 7 μM clusters and 0.1 M sodium perchlorate. The pH was adjusted with 5–500 mM perchloric acid.