FIG. 4.

Substrate kinetics of the reaction catalyzed by SHMT. (A) Reaction kinetics assessed using 1 μM purified SHMTwt, K251R, and K251Q proteins in the presence of 0.25 mM externally added PLP using variable concentration of THF. (B) Substrate kinetics of the reaction using SHMTwt and K251R under the same conditions in the absence of externally added PLP. The enzyme activity was measured by determining the incorporation of the radioactive label into methylenetetrahydrofolate by liquid scintillation spectroscopy. Error bars represent standard deviations of results from three measurements.