Comparison of RK(ROS) and RK(BV) Properties. (A) Temperature optimum. (B) pH optimum. Reaction conditions and assays for RK activity are described in the text. RK activity was measured by using urea-washed ROS membranes as the substrate. To determine the pH optimum, 50 mM BTP buffer was used instead of 20 mM BTP (the pH values were 5.63, 6.3, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, and 10.0).