Transfer of a sulfur ion to cyanide or to other thiol compounds. Also has weak rhodanese activity. Detoxifies cyanide and is required for thiosulfate biosynthesis. Acts as an antioxidant. In combination with cysteine aminotransferase (CAT), contributes to the catabolism of cysteine and is an important producer of hydrogen sulfide in the brain, retina and vascular endothelial cells. Hydrogen sulfide H(2)S is an important synaptic modulator, signaling molecule, smooth muscle contractor and neuroprotectant. Its production by the 3MST/CAT pathway is regulated by calcium ions. 2-oxo-3-sulfanylpropanoate + [thioredoxin]-dithiol = [thioredoxin]-disulfide + H(+) + hydrogen sulfide + pyruvate By oxidative stress, and thioredoxin. Under oxidative stress conditions, the catalytic cysteine site is converted to a sulfenate which inhibits the MPST enzyme activity. Reduced thioredoxin cleaves an intersubunit disulfide bond to turn on the redox switch and reactivate the enzyme. Inhibited by different oxidants, hydrogen peroxide and tetrathionate. Monomer (active form). Homodimer; disulfide-linked (inactive form). Expressed in liver, heart, kidney and brain. Localizes to tubular epithelium in the kidney, pericentral hepatocytes in the liver, cardiac cells in the heart and neuroglial cells in the brain. Also expressed in vascular endothelium of the thoracic aorta. Weak expression in lung and thymus. Contains two rhodanese domains with different primary structures but with near identical secondary structure conformations suggesting a common evolutionary origin. Only the C-terminal rhodanese domain contains the catalytic cysteine residue (By similarity). The N-terminus is blocked. Thioredoxin (Trx) or dihydrolipoic acid (DHLA) are required to release hydrogen sulfide from the persulfide intermediate.