Exogenous NO inhibits cell proliferation and protein biosynthesis. (A) Cell proliferation. L929 cells were cultured in 12-well plates until ∼70% confluence and cells were treated with either SNAP or oxidized SNAP solutions containing 5 µCi/ml 3H-thymidine for 18 hr. Some cells were treated with the NO scavenger oxyhemoglobin at 480 µM. 3H-thymidine incorporation into DNA was measured using a scintillation counter. (B) Protein synthesis. L929 cells were incubated with media containing SNAP or oxidized SNAP for 4 hr and then 35S-methionine was directly added into the culture media. After a 6 hr incubation, 35S-methionine incorporation into protein was measured after precipitation with TCA using a scintillation counter. All data are expressed as mean ± SD of more than two independent experiments, each performed in triplicate.