title: APRT from erythrocytes of HGPRT deficient patients: kinetic, regulatory and thermostability properties.
abstract: Adenine phosphoribosyltransferase (APRT) has been 1200-fold purified from erythrocytes of a patient with partial hipoxanthine-guanine phosphoribosyltransferase (HGPRT) deficiency, Propositus, and in those of a controlHPRT+, with 20% efficiency in both proteins and specific activity of 550 and 243 nmol/h/mgprotein. The specific activity determined in the Propositus enzyme was, in all purification steps, higher than that of the controlHPRT+. Significant changes were found in their thermal stabilities. Half inactivation times at each temperature studied are greater for the Propositus enzyme in the temperature interval 60-80 degrees C. No significant difference has been observed in the affinity constants for adenine and PRPP substrates. Studies on inhibition by the reaction product suggest that AMP is a competitive inhibitor with respect to PRPP in both enzymes, with Ki values of 150 microM in Propositus and 220 microM in controlHPRT+.
authors.affiliation: Instituto de Investigaciones Biomédicas del CSIC, Madrid, Spain.
authors.forename: Javier
authors.initials: J
authors.lastname: Crespillo
authors.forename: Pilar
authors.initials: P
authors.lastname: Llorente
authors.forename: Luisa
authors.initials: L
authors.lastname: Argomániz
authors.forename: Celia
authors.initials: C
authors.lastname: Montero
mesh_terms: D000225:Adenine / Q000378:metabolism; D000228:Adenine Phosphoribosyltransferase / Q000378:metabolism*; D001667:Binding, Competitive; D004305:Dose-Response Relationship, Drug; D004912:Erythrocytes / Q000201:enzymology*; D005192:Family Health; D005260:Female; D006801:Humans; D007041:Hypoxanthine Phosphoribosyltransferase / Q000172:deficiency*; D007700:Kinetics; D008297:Male; D010430:Pentosyltransferases / Q000378:metabolism; D011487:Protein Conformation; D013696:Temperature; D013816:Thermodynamics; D013997:Time Factors
chemical_list: D010430:Pentosyltransferases; C022484:purine phosphoribosyltransferase; D000228:Adenine Phosphoribosyltransferase; D007041:Hypoxanthine Phosphoribosyltransferase; D000225:Adenine