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Adenine Phosphoribosyltransferase

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Amrik Sahota – One of the best experts on this subject based on the ideXlab platform.

  • Adenine Phosphoribosyltransferase deficiency
    , 2015
    Co-Authors: Vidar O Edvardsson, Runolfur Palsson, Amrik Sahota

    Abstract:

    Clinical characteristics Adenine Phosphoribosyltransferase (APRT) deficiency is characterized by excessive production and renal excretion of 2,8-dihydroxyAdenine (DHA), which leads to kidney stone formation and crystal-induced kidney damage (i.e., DHA crystal nephropathy) causing acute kidney injury episodes and progressive chronic kidney disease (CKD). Kidney stones, the most common clinical manifestation of APRT deficiency, can occur at any age; in at least 50% of affected persons symptoms do not occur until adulthood. If adequate treatment is not provided, approximately 20%-25% of affected individuals develop end-stage renal disease (ESRD), usually in adult life. Diagnosis/testing The diagnosis of APRT deficiency is established in a proband by absence of APRT enzyme activity in red cell lysates or identification of biallelic pathogenic variants in APRT. The detection of the characteristic round, brown DHA crystals by urine microscopy is highly suggestive of the disorder. Management Treatment of manifestations: Treatment with the xanthine oxidoreductase inhibitors (XOR; xanthine dehydrogenase/oxidase) allopurinol or febuxostat can improve kidney function, even in individuals with advanced CKD. The prescribed dose of allopurinol and febuxostat should not routinely be reduced in affected individuals who have impaired kidney function. Ample fluid intake is advised. Surgical management of DHA nephrolithiasis is the same as for other types of kidney stones. ESRD is treated with dialysis and kidney transplantation. Even after kidney transplantation, treatment with an XOR is recommended. Surveillance: Measurement of eGFR and urinary DHA excretion (or urine microscopy for assessment of DHA crystalluria) every 6-12 months; routine follow up to facilitate adherence to pharmacologic treatment at least annually; periodic renal ultrasound examination should be considered to evaluate for new asymptomatic kidney stones. Agents/circumstances to avoid: Azathioprine and mercaptopurine should not be given to individuals taking either allopurinol or febuxostat. Evaluation of relatives at risk: It is recommended that sibs of an affected individual undergo APRT enzyme activity measurement or molecular genetic testing (if the pathogenic variants in a family have been identified) to allow early diagnosis and treatment and improve long-term outcome. Pregnancy management: The safety of allopurinol and febuxostat in human pregnancy has not been systematically studied. Some post-transplantation immunosuppressive therapies can have adverse effects on the developing fetus. Ideally a thorough discussion of the risks and benefits of maternal medication use during pregnancy should take place with an appropriate health care provider prior to conception. Genetic counseling APRT deficiency is inherited in an autosomal recessive manner. At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being normal. Carrier testing for at-risk relatives and prenatal diagnosis for pregnancies at increased risk are possible if the pathogenic variants in the family have been identified.

  • purification and characterization of Adenine Phosphoribosyltransferase from saccharomyces cerevisiae
    Biochimica et Biophysica Acta, 1997
    Co-Authors: Amrik Sahota, Juan D. Alfonzo, Milton W. Taylor

    Abstract:

    Adenine Phosphoribosyltransferase (APRT) from Saccharomyces cerevisiae was purified approximately 1500-fold. The enzyme catalyzes the Mg-dependent condensation of Adenine and 5-phosphoribosylpyrophosphate (PRPP) to yield AMP. The purification procedure included anion exchange chromatography, chromatofocusing and gel filtration. Elution of the enzyme from the chromatofocusing column indicated a pI value of 4.7. The molecular mass for the native enzyme was 50 kDa; however, upon electrophoresis under denaturing conditions two bands of apparent molecular mass of 29 and 20 kDa were observed. We have previously reported the presence of two separate coding sequences for APRT, APT1 and APT2 in S. cerevisiae. The appearance of two bands under denaturing conditions suggests that, unlike other APRTs, this enzyme could form heterodimers. This may be the basis for substrate specificity differences between this enzyme and other APRTs. Substrate kinetics and product inhibition patterns are consistent with a ping-pong mechanism. The Km for Adenine and PRPP were 6 μM and 15 μM, respectively and the Vmax was 15 μmol/min. These kinetic constants are comparable to the constants of APRT from other organisms.

  • Adenine Phosphoribosyltransferase-deficient mice develop 2,8-dihydroxyAdenine nephrolithiasis
    Proceedings of the National Academy of Sciences of the United States of America, 1996
    Co-Authors: Sandra J. Engle, Amrik Sahota, Ju Chen, Michael G. Stockelman, Gregory P. Boivin, M N Yum, Philip M. Davies, M Y Ying, H. A. Simmonds, Peter J. Stambrook

    Abstract:

    Adenine Phosphoribosyltransferase (APRT) deficiency in humans is an autosomal recessive syndrome characterized by the urinary excretion of Adenine and the highly insoluble compound 2,8-dihydroxyAdenine (DHA) that can produce kidney stones or renal failure. Targeted homologous recombination in embryonic stem cells was used to produce mice that lack APRT. Mice homozygous for a null Aprt allele excrete Adenine and DHA crystals in the urine. Renal histopathology showed extensive tubular dilation, inflammation, necrosis, and fibrosis that varied in severity between different mouse backgrounds. Thus, biochemical and histological changes in these mice mimic the human disease and provide a suitable model of human hereditary nephrolithiasis.

Milton W. Taylor – One of the best experts on this subject based on the ideXlab platform.

  • Structural analysis of Adenine Phosphoribosyltransferase from Saccharomyces cerevisiae.
    Biochemistry, 2001
    Co-Authors: Wuxian Shi, Milton W. Taylor, Kelly S.e. Tanaka, Timothy R. Crother, Steven C. Almo, Vern L. Schramm

    Abstract:

    Adenine Phosphoribosyltransferase (APRTase) is a widely distributed enzyme, and its deficiency in humans causes the accumulation of 2,8-dihydroxyAdenine. It is the sole catalyst for Adenine recycling in most eukaryotes. The most commonly expressed APRTase has subunits of approximately 187 amino acids, but the only crystal structure is from Leishmania donovani, which expresses a long form of the enzyme with 237 residues. Saccharomyces cerevisiae APRTase was selected as a representative of the short APRTases, and the structure of the apo-enzyme and sulfate bound forms were solved to 1.5 and 1.75 A, respectively. Yeast APRTase is a dimeric molecule, and each subunit is composed of a central five-stranded β-sheet surrounded by five α-helices, a structural theme found in all known purine Phosphoribosyltransferases. The structures reveal several important features of APRTase function:  (i) sulfate ions bound at the 5‘-phosphate and pyrophosphate binding sites; (ii) a nonproline cis peptide bond (Glu67−Ser68) at…

  • APT1, but Not APT2, Codes for a Functional Adenine Phosphoribosyltransferase in Saccharomyces cerevisiae
    Journal of bacteriology, 1999
    Co-Authors: Juan D. Alfonzo, Timothy R. Crother, Maria L. Guetsova, Bertrand Daignan-fornier, Milton W. Taylor

    Abstract:

    The yeast Saccharomyces cerevisiae has two separate genes (APT1 and APT2) that encode two potentially different forms of Adenine Phosphoribosyltransferase (APRT). However, genetic analysis indicated that only APT1 could code for a complementing activity. Cloning and expression of both the APT1 and APT2 genes in Escherichia coli showed that although discrete proteins (APRT1 and APRT2) were made by these genes, only APRT1 had detectable APRT activity. Northern and Western blot analyses demonstrated that only APT1 was transcribed and translated under normal physiological conditions in yeast. Phylogenetic analysis revealed that APRT1 and APRT2 are evolutionary closely related and that they arise from a gene duplication event. We conclude that APT1 is the functional gene in S. cerevisiae and that APT2 is a pseudogene.

  • purification and characterization of Adenine Phosphoribosyltransferase from saccharomyces cerevisiae
    Biochimica et Biophysica Acta, 1997
    Co-Authors: Amrik Sahota, Juan D. Alfonzo, Milton W. Taylor

    Abstract:

    Adenine Phosphoribosyltransferase (APRT) from Saccharomyces cerevisiae was purified approximately 1500-fold. The enzyme catalyzes the Mg-dependent condensation of Adenine and 5-phosphoribosylpyrophosphate (PRPP) to yield AMP. The purification procedure included anion exchange chromatography, chromatofocusing and gel filtration. Elution of the enzyme from the chromatofocusing column indicated a pI value of 4.7. The molecular mass for the native enzyme was 50 kDa; however, upon electrophoresis under denaturing conditions two bands of apparent molecular mass of 29 and 20 kDa were observed. We have previously reported the presence of two separate coding sequences for APRT, APT1 and APT2 in S. cerevisiae. The appearance of two bands under denaturing conditions suggests that, unlike other APRTs, this enzyme could form heterodimers. This may be the basis for substrate specificity differences between this enzyme and other APRTs. Substrate kinetics and product inhibition patterns are consistent with a ping-pong mechanism. The Km for Adenine and PRPP were 6 μM and 15 μM, respectively and the Vmax was 15 μmol/min. These kinetic constants are comparable to the constants of APRT from other organisms.

Jay A. Tischfield – One of the best experts on this subject based on the ideXlab platform.

  • Adenine Phosphoribosyltransferase Deficiency With Renal Deposition of 2,8-DihydroxyAdenine Leading to Nephrolithiasis and Chronic Renal Failure
    Archives of internal medicine, 1993
    Co-Authors: Kenneth H. Fye, Amrik Sahota, Ju Chen, Douglas C. Hancock, Arnold B. Gelb, Joel W. Sparks, Richard K. Sibley, Jay A. Tischfield

    Abstract:

    Homozygous Adenine Phosphoribosyltransferase deficiency is a genetic defect that is associated with 2,8-dihydroxyAdenine urolithiasis. Since the prevalence of the heterozygous state is found in 0.4% to 1.2% of the population, it is surprising that more cases of 2,8-dihydroxyAdenine urolithiasis have not been reported. Herein we describe a patient with complete Adenine Phosphoribosyltransferase deficiency with 2,8-dihydroxyAdenine urolithiasis leading to chronic renal failure. Gene sequencing revealed that the patient is a compound heterozygote. One of the mutations (a T insertion between bases 346 and 347) has been encountered before, but the second (a G-to-A substitution at base 1356) has not been previously reported. Possible explanations for the unexpected rarity of 2,8-dihydroxyAdenine urolithiasis are discussed. (Arch Intern Med. 1993;153:767-770)

  • Mutational basis of Adenine Phosphoribosyltransferase deficiency.
    Advances in experimental medicine and biology, 1991
    Co-Authors: Amrik Sahota, Ju Chen, Peter J. Stambrook, Jay A. Tischfield

    Abstract:

    Adenine Phosphoribosyltransferase (APRT, EC 2.4.2.7) catalyzes the synthesis of AMP from Adenine and 5-phosphoribosyl1-pyrophosphate. In APRT deficiency (McKusick 102600), Adenine is oxidized by xanthine oxidase to the highly insoluble and nephrotoxic derivative, 2,8-dihydroxyAdenine. The accumulation of this compound in the kidney can lead to stone formation and eventual renal failure (Simmonds et al. 1989).

  • 2,8-DihydroxyAdenine lithiasis in a Japanese patient heterozygous at the Adenine Phosphoribosyltransferase locus.
    American journal of human genetics, 1991
    Co-Authors: Amrik Sahota, Ju Chen, Peter J. Stambrook, M A Behzadian, R Ravindra, H Takeuchi, Jay A. Tischfield

    Abstract:

    Abstract
    All reported cases of 2,8-dihydroxyAdenine (DHA) lithiasis have been due to functional homozygous deficiency of Adenine Phosphoribosyltransferase (APRT). Here we describe the first case of DHA lithiasis in a patient who has functional APRT activity in cultured lymphoblasts. The patient is heterozygous for Japanese-type (type II) APRT deficiency as demonstrated by starch-gel electrophoresis and DNA sequence analysis. We also demonstrate the use of starch-gel electrophoresis for differentiation between the type II mutant enzyme and the wild-type enzyme.