Nitric oxide (NO) has been identified as an important endogenous inhibitor of apoptosis. This study investigates the mechanisms by which NO prevents hepatocyte apoptosis induced by growth factor withdrawal, TNFα, or anti-Fas antibody. The authors found that NO inhibits caspase-3-like protease activity, which is a key step in the apoptotic signaling cascade. They demonstrated that both endogenous and exogenous sources of NO prevent the increase in caspase-3-like activity in hepatocytes. Additionally, NO inhibits caspase-3-like activity through S-nitrosylation, a protein modification that directly affects enzyme activity. Furthermore, NO also prevents apoptosis via a cGMP-dependent mechanism, which functions at or upstream of the caspase-3-like protease activation level. These findings suggest that NO acts through multiple mechanisms to inhibit apoptosis, providing a comprehensive understanding of its antiapoptotic effects.Nitric oxide (NO) has been identified as an important endogenous inhibitor of apoptosis. This study investigates the mechanisms by which NO prevents hepatocyte apoptosis induced by growth factor withdrawal, TNFα, or anti-Fas antibody. The authors found that NO inhibits caspase-3-like protease activity, which is a key step in the apoptotic signaling cascade. They demonstrated that both endogenous and exogenous sources of NO prevent the increase in caspase-3-like activity in hepatocytes. Additionally, NO inhibits caspase-3-like activity through S-nitrosylation, a protein modification that directly affects enzyme activity. Furthermore, NO also prevents apoptosis via a cGMP-dependent mechanism, which functions at or upstream of the caspase-3-like protease activation level. These findings suggest that NO acts through multiple mechanisms to inhibit apoptosis, providing a comprehensive understanding of its antiapoptotic effects.