Aspartate and asparagine are catabolized into oxaloacetate and the Kreb's cycle in a fairly direct pathway for amino acids with four carbons. The first step for asparagine catabolism is hydrolysis by the enzyme asparaginase, releasing aspartate and ammonia. Aspartate is then transaminated by aspartate transaminase to exchange its amino group onto alpha-ketoglutarate and be converted into oxaloacetate. As part of the Kreb's cycle, the carbon skeleton of oxaloacetate can generate energy and provide material for biosynthesis.
The enzyme asparaginase is used as a cancer treatment through injection. Some cancers such as leukemias are highly dependent on asparagine circulating in the blood that comes from the diet. The required asparagine helps to support the rapid growth of malignant cells. Injection of asparaginase metabolizes the asparagine in the blood, withdrawing the supply of this essential nutrient from tumor cells, and causing asparagine-dependent tumor cells to die. Normal cells provide enough asparagine for their own needs through biosynthesis and are affected to a lesser extent by this treatment.
