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Figure 3


Fig. 3. Proposed mechanism of O2 sensing via H2S metabolism. H2S is constitutively produced from cysteine (Cys) metabolism in the cytosol. During normoxia (left panel) H2S is continuously oxidized to sulfite in the mitochondria thereby maintaining low intracellular [H2S]. A fall in oxygen availability (right panel) decreases mitochondrial H2S oxidation resulting in an increase in biologically active [H2S] and initiation of hypoxic responses. The enzymes generating H2S from cysteine, cystathionine β-synthase (CBS) and cystathionine {gamma}-lyase (CSE) also have the potential of O2 sensitivity, thereby enabling either short-term regulation of [H2S] or placing a long-term bias on the rate of H2S metabolism.