Argininosuccinate synthetase 1

Argininosuccinate synthetase is an enzyme that in humans is encoded by the ASS1 gene.

The protein encoded by this gene catalyzes the penultimate step of the arginine biosynthetic pathway. There are approximately 10 to 14 copies of this gene including the pseudogenes scattered across the human genome, among which the one located on chromosome 9 appears to be the only functional gene for argininosuccinate synthetase. Two transcript variants encoding the same protein have been found for this gene.

Clinical significance
Mutations in the chromosome 9 copy of ASS cause citrullinemia.

Arginine is considered a non-essential amino acid since normal cells can synthesize it from citrulline and aspartate using the enzymes argininosuccinate synthase 1 (ASS1) and argininosuccinate lyase (ASL). Consequently, depleting arginine can be an effective therapeutic approach. Notably, over 70% of tumors show reduced ASS1 transcription, making these cancer cells reliant on external sources of arginine, which forms the basis of arginine-deprivation therapy.

The investigational drug pegargiminase that degrades arginine is currently in trials for the treatment of ASS1 deficient cancers.