N-Acetylcysteine and Other Sulfur-Donors as a Preventative and Adjunct Therapy for COVID-19

Figure 2

Sulfur metabolism diagram. The essential sulfur amino acid methionine converts to cysteine, a precursor to albumin, cystine, coenzyme A, glutathione, hydrogen sulfite (H₂S), taurine, and sulfate (SO₄²⁻). H₂S can convert to thiosulfate (S₂O₃²⁻) and sulfite (SO₃²⁻), which are oxidised to sulfate. The enzyme cystathionine-β-synthase (CBS) converts homocysteine to cystathionine, while cysteine dioxygenase (CDO) is responsible for the conversion of cysteine to cysteine sulfinic acid. Sulfite oxidase (SUOX) oxidises sulfite to sulfate. H₂S is generated from cysteine by three different pathways through either CBS, cystathionine-γ-lyase (CSE), or 3-mercaptopyruvate sulfurtransferase (3-MST). Adapted with permission by CC by 4.0 [3].