FIG. 1.

Effect of the T-477-N substitution on IIA^Glc inhibition of glycerol kinase. Initial velocities of glycerol kinase catalyzed reactions were determined at pH 7.0 and 25°C as described in Materials and Methods. The points show the data that were obtained for the normal or T-477-N glycerol kinase and the lines show the fits of the data to the following equation:

where SA is specific activity, I_max is the maximum extent of inhibition and K_app is the apparent dissociation constant for IIA^Glc binding to glycerol kinase. The fits yield the following parameters for normal glycerol kinase: I_max, 96 ± 1%; K_app, 0.95 ± 0.06 μM. Those for T-477-N glycerol kinase are as follows: I_max, 96% (fixed); K_app, 370 ± 70 μM. Conditions: 2 mM glycerol, 2.5 mM ATP, 0.1 mM ZnCl₂, and IIA^Glc as indicated on the x axis. Enzyme concentration, 0.5 μg/ml. WT, wild type.