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A Radiochemical Assay for β-Ureidopropionase Using Radiolabeled N-Carbamyl-β-alanine Obtained via Hydrolysis of [2-14C]5,6-Dihydrouracil

1999; Elsevier BV; Volume: 272; Issue: 2 Linguagem: Inglês

10.1006/abio.1999.4181

1096-0309

André B. P. Kuilenburg, Henk van Lenthe, A. H. van Gennip,

Drug Transport and Resistance Mechanisms

A radiochemical assay was developed to measure the activity of beta-ureidopropionase in human liver homogenates which is based on the detection of the reaction product (14)CO(2) by liquid scintillation counting. Radiolabeled N-carbamyl-beta-alanine was prepared within 15 min by a simple hydrolysis of [2-(14)C]5, 6-dihydrouracil under alkaline conditions at 37 degrees C. The enzymatic reaction proved to be linear with time up to at least 3.5 h and protein concentrations up to at least 1 mg/ml. Human beta-ureidopropionase obeyed Michaelis-Menten kinetics with an apparent Km for N-carbamyl-beta-alanine of 15.5 +/- 1.9 microM. The assay proved to be very accurate and sensitive with an intraassay coefficient of variation of 2% and a detection limit of 28 pmol for the product CO(2).