Search

Summary. The second and third kindreds with hereditary haemolytic anaemia characterized by marked basophilic stippling of the erythrocytes, increased red-cell GSH and adenine nucleotides, and ribosephosphate pyrophosphokinase (RPK, PRPP synthetase) deficiency are reported. In each affected subject increased auto-haemolysis was not corrected by glucose additives in the autohaemolysis test. Despite the clearly hereditary nature of the syndrome, a heterozygous ‘carrier’ state could not be demonstrated in any family members. While autosomal recessive transmission is likely, the genetics remain obscure. The roles of substantial RPK deficiency as either a causative factor or an epiphenomenon is likewise not firmly established.

1. 1. The specific activity of phosphoribosyladenosine triphosphate: pyrophosphate phosphoribosyltransferase (phosphoribosyladenosine triphosphate synthetase) from Escherichia coli decreases with increasing concentration of the enzyme, indicating aggregation to less active forms. 2. 2. The decrease in specific activity at high enzyme concentrations is more pronounced at 35° than at 15°, and for this reason a very low activation energy for the synthetase reaction is found at high enzyme concentrations. 3. 3. 2.5 mM AMP inhibits the synthetase reaction under standard assay conditions and low enzyme concentrations while little inhibition is seen at high enzyme concentrations. Even at high enzyme levels, 2.5 mM AMP changes the response of the enzyme to histidine from a cooperative to a more hyperbolic type. 4. 4. At high enzyme concentrations, inhibition by the product, phosphoribosyladenosine triphosphate, is temperature dependent and most pronounced at low temperatures. 5. 5. The apparently sigmoidal response of synthetase activity to magnesium concentration may be explained by the binding of Mg2+ to ATP. After correction for this binding, half saturation of the enzyme with Mg2+ is observed at 0.13 mM.

The binding sites for the two cations essential for the catalytic function of 5-phospho-D-ribosyl alpha-1-diphosphate (PRPP) synthases have been identified from the structure of the Bacillus subtilis phosphoribosyldiphosphate synthetase (PRPPsase) with bound Cd(2+). The structure determined from X-ray diffraction data to 2.8-A resolution reveals the same hexameric arrangement of the subunits that was observed in the complexes of the enzyme with the activator sulfate and the allosteric inhibitor ADP. Two cation binding sites were localized in each of the two domains of the subunits that compose the hexamer; each domain of the subunit has an associated cation. In addition to the bound Cd(2+), the Cd(2+)-PRPPsase structure contains a sulfate ion in the regulatory site, a sulfate ion at the ribose-5-phosphate binding site, and an AMP moiety at the ATP binding site. Comparison of the Cd(2+)-PRPPsase to the structures of the PRPPsase complexed with sulfate and mADP reveals the structural rearrangement induced by the binding of the free cation, which is essential for the initiation of the reaction. The comparison to the cPRPP complex of glutamine phosphoribosylpyrophosphate amidotransferase from Escherichia coli, a type I phosphoribosyltransferase, provided information about the binding of PRPP. This strongly indicates that the binding of both substrates must lead to a stabilized conformation of the loop region, which remains unresolved in the known PRPPsase complex structures.

Background Phosphoribosyl pyrophosphate synthetase (PRS) I deficiency is a rare medical condition caused by missense mutations in PRPS1 that lead to three different phenotypes: Arts Syndrome (MIM 301835), X-linked Charcot-Marie-Tooth (CMTX5, MIM 311070) or X-linked non-syndromic sensorineural deafness (DFN2, MIM 304500). All three are X-linked recessively inherited and males affected display variable degree of central and peripheral neuropathy. We applied whole exome sequencing to a three-generation family with optic atrophy followed by retinitis pigmentosa (RP) in all three cases, and ataxia, progressive peripheral neuropathy and hearing loss with variable presentation. Methods Whole exome sequencing was performed in two affecteds and one unaffected member of the family. Sanger sequencing was used to validate and segregate the 12 candidate mutations in the family and to confirm the absence of the novel variant in PRPS1 in 191 controls. The pathogenic role of the novel mutation in PRPS1 was assessed in silico and confirmed by enzymatic determination of PRS activity, mRNA expression and sequencing, and X-chromosome inactivation. Results A novel missense mutation was identified in PRPS1 in the affected females. Age of onset, presentation and severity of the phenotype are highly variable in the family: both the proband and her mother have neurological and ophthalmological symptoms, whereas the phenotype of the affected sister is milder and currently confined to the eye. Moreover, only the proband displayed a complete lack of expression of the wild type allele in leukocytes that seems to correlate with the degree of PRS deficiency and the severity of the phenotype. Interestingly, optic atrophy and RP are the only common manifestations to all three females and the only phenotype correlating with the degree of enzyme deficiency. Conclusions These results are in line with recent evidence of the existence of intermediate phenotypes in PRS-I deficiency syndromes and demonstrate that females can exhibit a disease phenotype as severe and complex as their male counterparts. Electronic supplementary material The online version of this article (doi:10.1186/s13023-014-0190-9) contains supplementary material, which is available to authorized users.

The activity of phosphoribosylpyrophosphate synthetase and the rate of phosphoribosylpyrophosphate accumulation are significantly increased in cultured lymphocytes of Lesch Nyhan patients deficient in hypoxanthine guanine phosphoribosyltransferase and in a clone of mutagen-induced, hypoxanthine guanine phosphoribosyltransferase deficient human lymphocytes. The increase in phosphoribosylpyrophosphate synthetase activity is the cause of the abnormally high cellular phosphoribosylpyrophosphate content and possibly of the purine overproduction described in this syndrome.