L-Arginine versus D-arginine. Arginine stereochemistry had little effect on the nuclear activity of the R 8 À and (RB) 8 ÀPMO conjugates but affected the (RX) 8 ÀPMO ( Figure 5 ). Replacement of the eight L-arginine residues in R 8 À or (RB) 8 ÀPMO with D-arginine residues did not change the luciferase activity generated over the 1-5 mM ( Figure 5A and B) . However, the replacement did cause a small but statistically significant decrease in the activity for (RX) 8 ÀPMO at 1 mM (P = 0.03) and 2 mM (P = 0.01) ( Figure 5C ).