Still, 4 out of the 20 variants tested display substantially enhanced Kemp eliminase activity with respect to the background variant, both at pH 7 and pH 8.4. cases, the profiles are compared with that of the background GNCA4-WT (red data points). All data were obtained in the presence of 5% acetonitrile to increase the substrate concentration range, and to allow for a more accurate determination of the catalytic parameters (kcat in particular). Acetonitrile, however, has a slightly detrimental effect on activity (Figure ) and, therefore, the values given here for the "wild type" protein are somewhat lower than those previously reported in ref. . Agreement is observed, however, upon extrapolation to 0% acetonitrile (Figure ).