Hydrogen sulfide (H2S) produced endogenously has been established as the third gaseous signaling molecule, a smooth muscle relaxant and a neuroprotectant (Kimura 2011a, 2011b). Three enzyme systems produce H2S in the brain, retina and vascular endothelial cells (Shibuya et al. 2009a, 2009b, Mikami et al. 2011). 3-mercaptopyruvate sulphurtransferase (MPST, aka 3MST) in conjunction with cysteine (aspartate) aminotransferase (CAT, aka GOT2) is decribed here. In the second step, 3-mercaptopyruvate sulfurtransferase (MPST aka 3MST) mediates the transfer of a sulfur atom from 3-methylpryuvate (3MPYR) to hydrogensulfite (HSO3-) to form thiosulfate (S2O3(2-)) and pyruvate (PYR) (Yadav et al. 2013).