Figure 4.

Activation of PCS enzymes from model plants by physiologically relevant metals. A, Desalted crude extracts of AtPCS1 (200 μg of protein) were assayed (30 min) with 500 μm metal ions and 5 mm GSH. Values represent means ± se of three to six enzyme preparations and are expressed in percent relative to the PCS activities with Cd²⁺. The 100% value corresponds to a specific activity of 56 ± 7 nmol of total PCs (GSH equivalents) produced per minute per milligram of protein. B, Purified AtPCS1 (60 μg of protein) and LjPCS1 (60 μg of protein) were assayed (30 min) with 50 μm metal ions and 5 mm GSH. Values represent means ± se of four to eight enzyme preparations and are expressed in percent relative to the PCS activities with Cd²⁺. The 100% values correspond to specific activities of 87 ± 3 (AtPCS1) and 89 ± 14 (LjPCS1) nmol of total PCs (GSH equivalents) produced min⁻¹ mg⁻¹ of protein.