Figure 3.

Pathways of cysteine degradation to H₂S. Cysteine desulfhydrase is a key enzyme for initial microbial cysteine fermentation and pyruvate production. However, recent evidence indicates that three other enzymes orthologous to eukaryotic enzymes may catalyze similar reactions. The generation of H₂S via these four enzymatic pathways may surpass that by dissimilatory sulfate reduction, especially in hosts consuming a protein-rich diet.