Argininosuccinate synthetase activity in cultured human lymphocytes

Oksana Lockridge, Elaine B. Spector, Arthur D. Bloom

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


The activity of argininosuccinate synthetase (E.C., a urea cycle enzyme, was measured in cultured human lymphocytes using a new radioactive assay. Control cells had a maximum specific activity of 15.7±8.7 nmoles per hour per milligram of protein and an apparent Km for citrulline of 2 × 10-4m, whereas cells derived from a patient with citrullinemia had no detectable activity. A nutritional variant, selected out of the citrullinemic lymphocyte population by ability to grow in citrulline, had a maximum specific activity of 10.7±3.8 nmoles/hr/mg and an apparent Km for citrulline of 2 × 10-2m. These measurements confirm the observation that citrullinemia is associated with a defect in argininosuccinate synthetase activity and provide further evidence that citrullinemia is expressed in cultured lymphocytes. The emergence of a nutritional variant with a partial defect in argininosuccinate synthetase enzyme suggests that this citrullinemic patient has a heterogeneous population of cells, some totally defective and others only partially defective in argininosuccinate synthetase. The new activity assay is described in detail.

Original languageEnglish (US)
Pages (from-to)395-407
Number of pages13
JournalBiochemical Genetics
Issue number3-4
StatePublished - Apr 1977
Externally publishedYes


  • argininosuccinate synthetase
  • citrullinemia
  • human lymphocyte lines
  • urea cycle

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Biochemistry
  • Molecular Biology
  • Genetics


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