Figure 5. Substrate competition of the cyclization reaction.

(A) Increasing concentrations of NAD were allowed to compete with 100 μM (○), 30 μM (▵) or 10 μM (□) NGD under conditions as described in the Materials and methods section. The respective curves were fitted to the Hill equation. (B) IC₅₀ values obtained from (A) were plotted against the corresponding NGD concentration, and the data were fitted to a linear regression. (C) similar to (A) but with increasing concentrations of NADP competed with 100 μM (○), 30 μM (▵) or 10 μM (□) NGD. (D) IC₅₀ values obtained from (C) were plotted against the corresponding NGD concentration, analogous to (B). Results are means±S.D. for three experiments.