Figure 4.

Results of the real-time ³¹P NMR assay for measuring Adk activity. (A) The assay was initiated by adding Adk to ADP and Mg²⁺ at fixed concentrations. Depletion of ADP and accumulation of ATP and AMP were followed by recording ³¹P NMR spectra at indicated time points. Signals corresponding to ATP (blue), ADP (black), and AMP (red) were then integrated to obtain their concentrations at each time point (B). k_cat was calculated from the initial turnover rate, obtained by fitting the analytical solution (solid lines) for the rate equation to the observed concentrations (19).