FIGURE 4.

Properties of SPT enzymes containing wild-type and mutant LCB1 subunits. The serine K_m and the V_max of the wild-type (A) and HSAN1 C133W mutant (B) SPT enzymes were determined using [³H]serine as described under “Experimental Procedures.” The alanine K_m and V_max of the mutant enzyme was determined using [³H]alanine (C). The K_i values for alanine inhibition of serine utilization by the mutant and wild-type enzymes were determined by measuring the apparent K_m for serine in the presence of varying concentrations of unlabeled alanine (D).