(A) and (B): Inhibition of the deacetylation reaction by increasing concentrations of nicotinamide. (A) 500 ∝M H3 peptide, 250 ∝M NAD+ and 150 mM phosphate buffer, pH 7.3, quantified by integration of deacetylated product peaks in the HPLC chromatograms. (B) 200 ∝M p300 peptide, 400 ∝M NAD+ and 150 mM phosphate buffer, pH 7.5, and quantified by integration of deacetylated product peaks in the HPLC chromatograms. (C) and (D): Kinetics of the base-exchange chemistry catalyzed by Pf-Sir2 as measured by exchange of [carbonyl-14C]-nicotinamide into unlabeled NAD+. (C) 200 ∝M H3 peptide, 400 ∝M NAD+ and 150 mM phosphate buffer, pH 7.5. (D) 200 ∝M p300 peptide, 400 ∝M NAD+ and 150 mM phosphate buffer, pH 7.5.