Figure 3. Determination of pABA K_M for recombinant RFAP synthase. RFAP synthase activity was measured at a constant PRPP concentration of 8.8 mM while varying the pABA concentration from 181 µM to 36 mM. The inset shows the Lineweaver-Burke plot derived from the Michaelis-Menton plot. The estimated K_M for pABA was 4.5 mM and the V_max at 70 °C was approximately 190 nmol/min/mg protein.