Figure 7: Pathological implications of elevated HCys levels.

In some forms of cancer and some neurodegenerative diseases, disturbed HCys levels, in combination with perturbed homeostasis of redox-active transition metal ions, can lead to sulfheme formation without H2S intervention. Sulfheme formation occurs through the unprecedented S-oxygenation of HCys by the heme-oxo-iron(IV) of catalase. The resulting prosthetic heme modification induces an irreversible inhibition of catalase bioactivity and may participate to the aetiology of various disorders.