Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0018099 (gout)
 5,192 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In order to elucidate the regulatory functions of purine enzymes on the rate of purine biosynthesis, two phenotypically distinct mutant cell lines with altered IMP dehydrogenase activities were isolated from mutagenized cultures of mouse T-lymphoma (S49) cells. A single clone, MYCO-1A, was isolated from wild type S49 cells plated in semisolid agarose containing 1 microM mycophenolic acid. The MYCO-1A cell line was remutagenized, and a clone resistant to 20 microM mycophenolic acid, MYCO-1A-20, was isolated and characterized. Assays of IMP dehydrogenase activity in extracts prepared from mutant cells indicated that the enzyme behaved as a single kinetic species and that the maximal velocity of the mutant enzyme activity is 10-15-fold greater than that obtained from wild type extracts. Altered apparent Km values for substrates and the lack of normal sensitivity to mycophenolic acid of the enzymes from mutant cells imply that the mutants have an alteration in a structural gene coding for IMP dehydrogenase. Measurements of intracellular nucleotides indicated that the mycophenolic acid-resistant clones contained elevated levels of GMP and GTP. Incubation of wild type cells with 1 microM mycophenolic acid caused a depletion of intracellular GTP and GMP levels, an increase in the concentration of IMP, an increase in the total rate of de novo purine synthesis, and a massive excretion of inosine into the culture medium. Similar effects were found for MYCO-1A cells incubated with 5 microM, but not 1 microM, mycophenolic acid. However, neither purine overproduction nor nucleotide pool perturbations were observed for MYCO-1A-20 cells incubated with 25 microM mycophenolic acid. These results suggest that a genetic defect in IMP dehydrogenase activity in humans might lead to excessive purine overproduction with subsequent hyperuricemia and gout.
 ...
PMID:Characterization of mutant murine lymphoma cells with altered inosinate dehydrogenase activities. 612 53

Alterations in several specific enzymes have been associated with increased rates of purine synthesis de novo in human and other mammalian cells. However, these recognized abnormalities in humans account for only a few percent of the clinical cases of hyperuricemia and gout. We have examined in detail the rates of purine production de novo and purine excretion by normal and by mutant (AU-100) murine lymphoma T cells (S49) 80% deficient in adenylosuccinate synthetase [IMP:L-aspartate ligase (GDP-forming), EC 6.3.4.4]. The intracellular ATP concentration of the mutant cells is slightly diminished, but their GTP is increased 50% and their IMP, four-fold. Compared to wild-type cells, the AU-100 cells excrete into the culture medium 30- to 50-fold greater amounts of purine metabolites consisting mainly of inosine. Moreover, the AU-100 cell line overproduces total purines. In an AU-100-derived cell line, AU-TG50B, deficient in adenylosuccinate synthetase and hypoxanthine/guanine phosphoribosyltransferase (IMP:pyrophosphate phosphoribosyltransferase, EC 2.4.2.8), purine nucleoside excretion is increased 50- to 100-fold, and de novo synthesis is even greater than that for AU-100 cells. The overexcretion of purine metabolites by the AU-100 cells seems to be due to the primary genetic deficiency of adenylosuccinate synthetase, a deficiency that requires the cell to increase intracellular IMP in an attempt to maintain ATP levels. As a consequence of elevated IMP pools, large amounts of inosine are secreted into the culture medium. We propose that a similar primary genetic defect may account for the excessive purine excretion in some patients with dominantly inherited hyperuricemia and gout.
 ...
PMID:Purine oversecretion in cultured murine lymphoma cells deficient in adenylosuccinate synthetase: genetic model for inherited hyperuricemia and gout. 695 54

In man, there are at least four isoforms of adenosine monophosphate deaminase (AMPD): myoadenylate deaminase in skeletal muscle, the L isoform in liver, and the E1 and E2 isoforms in erythrocytes. Myoadenylate deaminase is encoded by the AMPD1 gene located on chromosome 1 p13-p21, the L isoform by the AMPD2 gene, and both isoforms in erythrocytes by the AMPD3 gene. Myoadenylate deaminase deficiency is found in 2-3% of all muscle biopsies. The inborn type of myoadenylate deaminase deficiency is caused by a single mutant allele harbouring two mutations: C34-->T (Gln-->Stop) and C143-->T (Pro-48-->Leu). Population studies revealed a frequency of the mutant allele of 0.12 in Caucasian Americans and Germans. The C34-->T mutation is located in exon 2, which is alternatively spliced in part of the AMPD1 transcript in human muscle. Since the second mutation does not affect enzyme function, alternatively spliced mRNA encodes a catalytically active enzyme. Only one patient with a disorder linked to liver AMPD has been described so far. In this patient the decreased inhibition of this enzyme by GTP resulted in uric acid overproduction and gout. A complete lack of erythroyte AMPD activity is found in asymptomatic subjects. The molecular basis of both disorders is not yet known.
 ...
PMID:Molecular biology of AMP deaminase deficiency. 803 42