Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) is inactivated by S-sulfuration in vitro

Hydrogen sulfide (H2S) is produced enzymatically by cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE), as well as other enzymes in mammalian tissues. These discoveries have led to the crowning of H2S as yet another toxic gas that serves as a gasotransmitter like NO and CO. H2S is thought to exert its biological effects through its reaction with cysteine thiols in proteins, yielding sulfurated thiol (-SSH) derivatives. One of the first proteins shown to be modified by H2S was glyceraldehyde 3-phosphate dehydrogenase (GAPDH) [1] where the S-sulfuration of the active site cysteine (Cys 152) resulted in ~7-fold increase in the activity of the enzyme. In the present study we have attempted to reproduce this result with no success. GAPDH in its reduced, or hydrogen peroxide, or glutathione disulfide, or nitrosonium oxidized forms was reacted with sulfide or polysulfides. Sulfide had no effect on reduced GAPDH activity, while polysulfides inhibited GAPDH to ~42% of control. S-sulfuration of GAPDH occurred at Cys 247 after sulfide treatment, Cys 156 and Cys 247 after polysulfide treatment. No evidence of S-sulfuration at active site Cys 152 was discovered. Both sulfide and polysulfide was able to restore the activity of glutathione disulfide oxidized GAPDH, but not to control untreated levels. Treatment of glutathione disulfide oxidized GAPDH with polysulfide also produced S-sulfuration of Cys 156. Treatment of a C156S mutant of GAPDH with sulfide and polysulfide resulted in S-sulfuration of Cys 152, which also caused a decrease and not an increase in enzymatic activity. Computational chemistry shows S-sulfuration of Cys 156 may affect the position of catalytic Cys 152, raising its pKa by 0.5, which may affect the nucleophilicity of Cys 152. The current study raises significant questions about the reported ability of H2S to activate GAPDH by the sulfuration of its active site thiol, and indicates that polysulfide is a stronger protein S-sulfurating agent than sulfide.