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  • Title: Argininosuccinate synthetase activity in cultured human lymphocytes.
    Author: Lockridge O, Spector EB, Bloom AD.
    Journal: Biochem Genet; 1977 Apr; 15(3-4):395-407. PubMed ID: 869901.
    Abstract:
    The activity of argininosuccinate synthetase (E.C. 6.3.4.5), 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 X 10(-4) M, 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 X 10(-2) M. 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.
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