Figure 3

Titration of DHO-ATC and apo-DHO-ATC with zinc and cobalt. The DHO-ATC complex in 0.05 mM TrisHCl, pH 7.4 was titrated with zinc chloride (■) and with cobalt chloride (□) and the catalytic activity was assayed with a dihydroorotate concentration of 8 mM at 72°C. The metal ion was removed from the DHO subunit by dialysis against pyridine-2, 6-dicarboxylate and the DHO-ATC complex was reconstituted (Methods). The apoezyme was then titrated with zinc (●) and with cobalt (□) and assayed.