Hypoxanthine-guanine phosphoribosyltransferase. Characterization of a mutant in a patient with gout.

Abstract

ABSTRA CT The mutation in a young gouty male with a partial deficiency of hypoxanthine-guanine phosphoribosyltransferase has been evaluated. The serum uric acid was 11.8 mg/100 ml, and the urinary uric acid excretion was 1,279 mg/24 h. Erythrocyte hypoxanthine-guanine phosphoribosyltransferase was 34.2 nmol/h/mg, adenine phosphoribosyltransferase was 36.5 nmol/h/mg and phosphoribosylpyrophosphate was 2.6 AM. Hypoxanthine-guanine phosphoribosyltransferase from peripheral leukocytes and cultured diploid skin fibroblasts was within the normal range, but enzyme activity in rectal mucosa was below the normal range.Initial velocity studies of the normal enzyme and the mutant enzyme from erythrocytes with the substrates hypoxanthine, guanine, or phosphoribosylpyrophosphate showed that the Michaelis constants were similar. Product inhibition studies distinguished the mutant enzyme from the normal enzyme. Hyperbolic kinetics with increasing phosphoribosylpyrophosphate were converted to sigmoid kinetics by 0.2 mM GMP with the mutant enzyme but not with the normal enzyme.The mutant erythrocyte hypoxanthine-guanine phosphoribosyltransferase was inactivated normally at 80'C and had a normal half-life in the peripheral circulation. The mol wt of 48,000 was similar to the normal enzyme mol wt of 47,000. With isoelectric focusing, the mutant erythrocyte enzyme had two major peaks with isoelectric pH's of 5.50 and 5.70, in contrast to the isoelectric pH's of 5.76, 5.82, and 6.02 of the normal isoAn abstract of this work was published in Clin. Res. 22: 389a, 1974. Dr.

Partial deficiency of hypoxanthine‐phosphoribosyltransferase:evidence for a structural mutation in a patient with gout

“…as normal HPRT in sucrose gradient ultracentrifugation. This situation is similar t o the case examined by Fox et al [2]. The thermal stability of the mutant enzyme is increased in haemolysates and decreased in fibroblast lysates.…”

“…Because the residual activity is measurable these partially deficient cases have lent themselves to the study of the properties of the mutant enzyme (or enzymes). Thus mutant HPRT has been characterized in a variety or ways; differences in residual activity, in kinetic and electrophoretic properties [2][3][4], in enzyme stability [5] and in immunological reactivity [ 6 , 71 have been described and reveal a considerable heterogeneity. The presence of a normal amount of material cross-reacting with anti-HPRT serum seems t o be the exception rather than the rule [6,71.…”

Hprt: Gene Structure, Expression, and Mutation

“…First reports characterizing HPRT deficiency in human cell lysates described enzymatic data suggestive of mutational heterogeneity (66,92). These changes included altered sensitivity to product inhibition, thcrmolability, Km value alterations, and changes in electrophoretic mobility (6,10,25,34,38,50,66,92,96). With the development of effective purification and protein sequencing protocols, Wilson et al have been able to compare amino acid sequence data from three HPRT deficient patients with gouty arthritis and one Lesch-Nyhan patient (Figure 4; see also 104,107,108,110).…”

Human hypoxanthine-guanine phosphoribosyltransferase. Detection of a mutant allele by restriction endonuclease analysis.

“…The clinical, genetic, and biochemical features of the P. family have been described (11)(12). A partial pedigree of this kindred is shown in Fig.…”