(A) Initial rate of AppA synthesis for different substrate ratios at 10°C; plotted versus (2MeImpA)/(pA). Total nucleotide is constant: (2MeImpA) + (pA) = 20 mM. (Upper points, solid line) Rate of the reaction with poly(U); (lower points, dotted lines) reaction without polymer. (Lower dotted curves) Rates of reaction calculated for the lower reaction if rate goes as (2MeImpA) × (pA) (curve labeled 1 at right), rate goes as (2MeImpA)2 × (pA)2 (labeled 2), as (2MeImpA)3 × (pA)3 (labeled 3), and as (2MeImpA)4 × (pA)4 (labeled 4 at right). (B) Example of fit (dotted lines) to data (points) by the mechanism given for simultaneous chemical and poly(U)-catalyzed AppA synthesis, with concurrent hydrolysis of 2MeImpA to pA. Data are for initial concentrations of 12 mM 2MeImpA, 8 mM pA [and 5 mM poly(U) phosphate for the upper data], as shown in Figure 6A.
