FIG 7.

The variant ChPPK/A79G/S106C/I108F/L285P exhibited improved thermal (A) and pH stability (B) compared to the wild-type ChPPK. For determining thermal stability, 5 µg/mL purified enzymes were incubated at 45°C for various periods. After incubation, an enzymatic activity assay was performed at 37°C. One unit of enzyme activity was given as the amount of enzyme that synthesized 1 µM ATP from AMP per minute during the initial minute. The activity of unheated enzymes was taken as 100%. For determining pH stability, 50 µg/mL purified enzymes were preincubated in 50 mM potassium phosphate buffer (pH 6.0–7.0) at 4°C for 6 h. One unit of enzyme activity was given as the amount of enzyme that synthesized 1 µM ATP from AMP per minute during the initial minute. The activity of enzymes preincubated in 50 mM potassium phosphate buffer (pH 7.5) was taken as 100%.