| Sumario: | The accumulation of argininosuccinate by an arg-10 mutant of Neurospora crassa is enhanced when growth-limiting amounts of arginine are used, or when citrulline is supplied in addition to non-limiting concentrations of arginine. Elevated levels of ornithine carbamoyl transferase (carbamoyl phosphate: l-ornithine carbamoyl transferase, EC 2.1.3.3) are found under circumstances leading to accumulation of argininosuccinate. An explanation based on the possibility that citrulline might impose a limited availability of arginine has been excluded. Indeed, the mutant displays a higher mycelial pool of arginine, and an increased consumption of this amino acid when it is grown with added citrulline. It is emphasized that elevated (derepressed) levels of ornithine carbamoyl transferase prevail under these conditions. © 1967.
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