Fig. (2) Mutant enzyme relative specificity differences compared to wild-type enzyme for ganciclovir. Using the equation, (k_cat/K_{m (GCV)})/((k_cat/K_{m (GCV)}) + (k_cat/K_{m (dT)})), the relative specificities were calculated. This equation takes into account the presence of endogenous thymidine that could compete with prodrug for the active site. The data are plotted as the fold increase from wild-type enzyme. Mutant 30 and SR39 values have been taken from Kokoris et al. [17] and [22], respectively.