Fig. 4.

Intracellular levels of reduced and total biopterins in siRNA-transfected endothelial cells. A: endothelial cells were transfected with siRNA constructs targeting GR, TrxR1, TrxR2, or a control sequence, and intracellular levels of tetrahydro-l-biopterin (BH4) and total biopterins were assessed by differential oxidation and HPLC. The open bars indicate the concentration of total cellular biopterins, and the solid bars indicate the concentration of reduced biopterins (BH4). B: fraction of intracellular BH4 relative to the total biopterins level. Each data point represents the mean ± SE derived from three independent experiments, each performed in duplicate. *P < 0.01, vs. control siRNA-transfected cells (ANOVA).