title: Intermediary purine-metabolizing enzymes from the cytosol of Dictyostelium discoideum monitored by high-performance liquid chromatography.
abstract: The use of high-performance liquid chromatography to identify and quantitate five purine-metabolizing enzymes from a partially purified subcellular fraction of the eucaryotic microorganism Dictyostelium discoideum is described. All HPLC separations were carried out in an isocratic manner using reverse-phase C18 as the stationary phase. The mobile phase consisted of a phosphate buffer with either methanol or acetonitrile as cosolvent, and optimal separation conditions were attained by varying the organic concentration or the pH of the buffer or by employing paired-ion chromatographic techniques. Substrates and products were detected at either 254 nm for the purines or 295 nm for the formycin analogs. An adenosine kinase activity was identified, and it was demonstrated that formycin A (FoA) could be substituted for adenosine as the phosphate acceptor, yielding FoAMP as the product. With FoA as the substrate an apparent Km of 18.2 microM and an apparent Vmax of 32.4 mmol min-1 mg-1 were observed for the activity. A purine-nucleoside phosphorylase activity was found to cleave adenosine to adenine and ribosylphosphate. FoA was not found to be a substrate for this activity due to the unusual formycin C-glycosyl bond which was not hydrolyzed by enzymes or chemically with either HCl or NaOH. An adenylate deaminase activity was found to be present in the cytosolic S-100 of cells harvested during the onset of development, and this deaminase activity was greatly stimulated by ATP. With FoAMP as the substrate, an apparent Km of 236 microM and Vmax of 2.78 mumol min-1 mg-1 were observed. The deamination of FoAMP could be inhibited by the addition of the natural substrate AMP. An apparent Ki value of 136 microM was determined from initial rate data. An adenylosuccinate synthetase activity was observed to have a Km value for GTP, IMP, and aspartic acid of 23, 34, and 714 microM, respectively. The formycin analog FoIMP was not a substrate with this activity but was a competitive inhibitor of IMP. Finally hypoxanthine-guanine phosphoribosyltransferase was found to have Km and Vmax values for hypoxanthine of 55.5 microM and 34.3 nmol-1 min-1 mg-1. When guanine was used as the substrate, the rate of nucleotide formation was 50% that with hypoxanthine as the substrate. The advantages of using HPLC to examine the interconnecting activities of a multienzyme complex in subcellular fractions are discussed, including the increased sensitivity obtained by using formycin analogs in the assay procedures.(ABSTRACT TRUNCATED AT 400 WORDS)
mesh_terms: D000659:AMP Deaminase / Q000378:metabolism; D000248:Adenosine Kinase / Q000378:metabolism; D000265:Adenylosuccinate Synthase / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003600:Cytosol / Q000201:enzymology*; D004023:Dictyostelium / Q000201:enzymology* / Q000254:growth & development; D007041:Hypoxanthine Phosphoribosyltransferase / Q000378:metabolism; D007700:Kinetics; D011683:Purine-Nucleoside Phosphorylase / Q000378:metabolism; D011687:Purines / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D011687:Purines; D011683:Purine-Nucleoside Phosphorylase; D007041:Hypoxanthine Phosphoribosyltransferase; D000248:Adenosine Kinase; D000659:AMP Deaminase; D000265:Adenylosuccinate Synthase