(2) Arginine metabolism: ASS1 is recognised as the rate-limiting enzyme in arginine synthesis, and in many cancers, including hepatocellular carcinoma, melanoma, prostate cancer, and renal cancer, ASS1 expression is downregulated or even absent, thus preventing cells from synthesising arginine and making them dependent on exogenous arginine. The gene discussed is ASS1; the disease is prostate cancer.