Adenine, hypoxanthine and guanine metabolism in fibroblasts from normal individuals and from patients with hypoxanthine phosphoribosyltransferase deficiency

Abstract

The metabolism of adenine, hypoxanthine, and guanine was studied in normal fibroblasts and in fibroblasts from patients with the Lesch-Nyhan syndrome, deficient in hypoxanthine phosphoribosyltransferase activity. The cells were incubated with a radioactive purine base and the incorporation of radioactivity into all major purine nucleotides, nucleosides and bases, as well as nucleic acids, was determined. All three bases were avidly taken up and converted to nucleotides by normal cells. In the mutant cells, nucleotide synthesis from hypoxanthine and guanine was less than 2 % of normal, whereas, adenine was metabolized normally. At higher concentrations of hypoxanthine and guanine, increased utilization was demonstrated in both normal and mutant fibroblasts by direct ribosylation, probably catalyzed by nucleoside phosphorylase. The conversion of total adenine nucleotide radioactivity to guanine nucleotides was less than 2 % in the normal and less than 5 % in the mutant cells, when [ 14C]adenine was used as the substrate. Less than 10 % of total utilization of adenine and hypoxanthine was found in nucleic acids after a 6-h incubation in cells grown to confluency. The conversion of guanine to adenine nucleotides was either undetectable or below 1 % of total guanine nucleotide radioactivity. IMP was channeled mainly to adenine nucleotide synthesis. No free adenine was formed from hypoxanthine or guanine. Xanthine oxidase activity was not present in either type of cell, and inosine kinase could not be demonstrated in hypoxanthine phosphoribosyltransferase-deficient fibroblasts.