Effect of l-arginine deprivation in the medium on K562 cell growth under stimulation with sodium butyrate. K562 cells were seeded in 12-well plates at a density of 1 × 10⁵ cells/mL and incubated in culture medium with or without l-arginine for 5 days. • represents l-arginine⁺ butyrate⁺; ○, l-arginine⁺ butyrate^-; ▪, l-arginine^- butyrate⁺; and □, l-arginine^- butyrate^-. (A) Time course of benzidine-positive cells ratio of K562. (B) Time course of cell number of K562 cells. Experiments were repeated 3 times with similar results.