Fig. 4.
Experimental data of [1′-14C]guanosine trapping in the Michaelis complex of PNPs. The ordinate shows the amount of bound reactant committed to product formation in the phosphorolysis of guanosine by PNPs. Equilibrated mixtures of 25 μM PNPs and 80 μM [1′-14C]guanosine (Fig. S5) were mixed with excess guanosine and phosphate at time = 0. The amount of [1′-14C]guanosine converted to [1-14C]α-d-ribose 1-phosphate was extrapolated to t = 0 and compared with the initial PNP-[1′-14C]guanosine concentration to calculate Y of Table 2. Guanosine commitment for light and heavy native PNP are shown in A and B, respectively. Guanosine commitment for light and heavy F159Y PNP are shown in C and D, respectively. The values of Y and Cf are summarized in Table 2.