This information can be found in the manual. Dilutions of NAD+ (BML-KI282, 50mM) in Assay Buffer (BML-KI286) have to be prepared and they will be 3.33X the desired final concentrations. For inhibitor screening, substrate concentrations at or below the Km are recommended. The Km for NAD+ was determined to be 558µM. Please see Figure 7 of the kit insert.