FIGURE 5.

Cleavage of the C75ΔC41Δ variant of TGR1 is rescued with increasing concentrations of cytosine and cytosine analogs. In the absence of exogenous base, the rate of cleavage at pH 7.0 (40 mM AMT buffer) was < 6 × 10⁻⁶ min⁻¹ (filled circles). Data is shown for isocytosine at 5, 10, and 20 mM (triangles), cytosine at 10, 20, and 37 mM (circles) (AMT buffer at pH 7.0), and 2-aminopyridine at 50, 100, and 250 mM (pH 7.3, no additional buffering) (squares). Pseudo first-order rate constants ranged from ∼3 × 10⁻⁴ to 1 × 10⁻² min⁻¹ for the rescue reactions shown.