CBS and malignant colon neoplasm: Interestingly, it is well known that the enzyme cystathionine-β-synthase (CBS) can produce hydrogen sulfide (H2S) and is selectively up-regulates in colon cancer cells, thus, the concentration of H2S in colon cancer tissues (0.3-3.4 mmol L-1) is considerably higher than that in non-tumor tissues 3-7.