Steady-state Ap3A cleavage by NPP4. (A) Time courses of Ap3A cleavage monitored by absorbance at 259 nm after mixing 200nM NPP4 with (bottom to top) 2, 44, 125, and 250μM Ap3A. (B) [AP3A]–dependent steady-state AP3A cleavage rate by NPP4 (200nM). The solid line through the data represents the best fit to a rectangular hyperbola.