Adenylosuccinate Synthase (ADSS)

Alignment with the sequence of the ADSS gene in mouse, Dictyostelium discoideum, and E. coli pointed to invariant residues that are likely to be important for structure and/or catalysis. The human ADSS sequence also showed some similarity to argininosuccinate synthetase, which catalyzes a chemically similar reaction.

Somatic cell hybrids between human cells and Chinese hamster ovary (CHO) cells deficient in specific steps in the purine biosynthetic pathway permitted mapping of human genes correcting the defects. The ade(-)H mutant is missing the enzyme adenylosuccinate synthetase (ADSS), which carries out the first of a 2-step sequence in the biosynthesis of AMP from IMP. Thus, ade(-)H cells require exogenous adenine for growth.