substrate for omega amidase, but KGM exists mainly in the ring form at physiological conditions. Omega-amidase has a higher affinity for the open linear form of KGM that forms more readily at pH 8.5. GTK catalyzes a reversible reaction, but coupling it with omega-amidase makes the transamination reaction irreversible at physiological conditions. Due to omega-amidase's ability to convert toxic substrates like KGM into components that can be used by other processes, this enzyme can be considered a repair enzyme. Some such substrates are linked to diseases or conditions such as hyperammonemia. A list of some of the substrates that omega-amidase catalyzes may be found in Table 1. Medical relevance The NIT2 gene in humans has been found to be identical to omega-amidase. The gene has the highest expression in the liver and kidney, but is also expressed in almost every human tissue. Overexpression of the NIT2 gene results in decreasing cell proliferation and growth in HeLa cells, which indicates that the gene may have a role in tumor suppression. However further studies are necessary to determine the effect on specific cancers, as a study done with colon cancer cells showed that downregulation of NIT2 induced cell cycle arrest. In addition to tumor suppression, NIT2/omega-amidase may be useful for detection and conversion of oncometabolites. Because omega-amidase is able to control concentration of toxic substrates such as KGM, it is likely that NIT2 can serve the same purpose. References Further reading EC 3.5.1 Enzymes of unknown structure