Figure 4.

Effect of L-tyrosine concentration on tyrosinase (tyrosine hydroxylase) activity in transfected HeLa cells. Assay conditions were as described in the legend to Figure 3, except that the time of incubation was fixed at 6 hours, and the concentration of L-tyrosine was varied. For symbols, see legend to Figure 3. To determine the Km and Vmax, tyrosinase activities were assayed at 0.05, 0.1, 0.2, 0.3, and 0.4 mM L-tyrOsine (○; ▴; and ▵) or 0.05, 0.1, and 0.15 mM L-tyrosine (•) concentrations at 37°C (data not shown).