Hydrogen polysulfides (H2Sn, where n>=2) are also endogenously produced by 3-mercaptopyruvate sulfurtransferase (MPST aka 3MST) directly from 3-mercaptopyruvate (3MPYR) generated by cysteine (aspartate) aminotransferase (GOT2) (Kimura et al. 2013, Kimura et al. 2015, Koike et al. 2017). Where n=2, the H2S2 species is called hydrogen persulfide (aka disulfane). MPST can release either H2S or H2Sn depending on the interaction with thioredoxin. When there is strong interaction with thioredoxin, H2S is released. 3MST receives sulfur from 3MPYR to persulfurate (oxidise) cysteine-248 residue of its reaction centre.
H2S2 is the dominant form produced with H2S3 detected at lower concentrations in cells or tissues. Up to H2S35 may exist (Steudel 2003), but under physiological conditions, when n reaches 8, it forms a crown shape and precipitates. H2Sn activate transient receptor potential ankyrin 1 (TRPA1) channels (Kimura et al. 2013), facilitate translocation of nuclear factor like-2 (NRF2) to the nucleus by modifying its binding partner kelch-like ECH-associated protein 1 (KEAP1) (Koike et al. 2013), regulates the activity of the tumor suppressor phosphatase and tensin homolog (PTEN) (Greiner et al. 2013), and reduces blood pressure by activating protein kinase G1a (Stubbert et al. 2014). Another persulfurated molecule, cysteine persulfide, which may be involved in the regulation of cellular redox homeostasis, is also produced by MPST (Kimura et al. 2017).