Assay for beta-ureidopropionase by high-performance liquid chromatography

Amidohydrolases of the reductive pyrimidine catabolic pathway purification, characterization, structure, reaction mechanisms and enzyme deficiency

In the reductive pyrimidine catabolic pathway uracil and thymine are converted to beta-alanine and beta-aminoisobutyrate. The amidohydrolases of this pathway are responsible for both the ring opening of dihydrouracil and dihydrothymine (dihydropyrimidine amidohydrolase) and the hydrolysis of N-carbamyl-beta-alanine and N-carbamyl-beta-aminoisobutyrate (beta-alanine synthase). The review summarizes what is known about the properties, kinetic parameters, three-dimensional structures and reaction mechanisms of these proteins. The two amidohydrolases of the reductive pyrimidine catabolic pathway have unrelated folds, with dihydropyrimidine amidohydrolase belonging to the amidohydrolase superfamily while the beta-alanine synthase from higher eukaryotes belongs to the nitrilase superfamily. beta-Alanine synthase from Saccharomyces kluyveri is an exception to the rule and belongs to the Acyl/M20 family.

A radiochemical assay for beta-ureidopropionase using radiolabeled N-carbamyl-beta-alanine obtained via hydrolysis of [2-(14)C]5, 6-dihydrouracil

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).

Determination of enzyme activity by high-performance liquid chromatography

The application of high-performance liquid chromatography (HPLC) in the study of enzymatic reactions is reviewed. The rationale for using HPLC is given and whether the components of the reaction mixture should be derivatized prior to or after HPLC. An alphabetical list of enzymes assayed by HPLC is given. Substrate and product are included as well the derivatization reagent, detection method and biological matrix. Specific examples of these assays in a complex biological matrix viz. faeces are given. Future prospects are the detection of new enzymes using synthetic substrates and implementation of mass spectrometry to elucidate enzyme specificities.

High-performance liquid chromatography-based assays of enzyme activities

Interest in using HPLC to assay enzymatic reactions continues to grow as evidenced by the more than 100 papers published during the early 1990s. HPLC can be used for any enzymatic assay that requires separation of substrates and products before quantifying the extent of the reaction. The popularity of HPLC-based assays is due to several reasons: (1) HPLC offers unsurpassed precision, specificity, sensitivity, and reproducibility. (2) Powerful microcomputers and user-friendly software automate the running of samples and collection and processing of data. (3) Current columns, especially C18 packings, separate a very wide variety of samples, and (4) A variety of on-line detectors provide a means to detect virtually any compound. This review surveys recent papers on the development of HPLC-based assays for enzymes that degrade or otherwise modify macromolecules. Methods for assaying enzymes involved in metabolic pathways are also reviewed. Work by the authors in developing HPLC-based assays for mitochondrial enzymes that use GTP/GDP and other nucleotides that cannot be or are not easily assayed by enzyme-coupled assays is discussed. These enzymes include nucleoside diphosphate kinase, succinate thiokinase, and GTP-AMP phosphotransferase. The assays are suitable for determining the submitochondrial compartmentation of enzyme activities. Finally, current and anticipated trends in HPLC technology, including new column packings and the trend toward smaller columns that give faster separations, are reviewed in relation to enzyme assays.