Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0025362 (mental retardation)
 15,878 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Adenylosuccinate adenosine 5'-monophosphate lyase (EC 4.3.2.2; ASL) catalyzes two distinct reactions in adenosine 5'-monophosphate (AMP) biosynthesis. A S413P mutation in ASL segregates with mental retardation in an affected family (Stone, R. L., Aimi, J., Barshop, B. A., Jaeken, J., Van den Berghe, G., Zalkin, H., and Dixon, J. E. (1992) Nature Genet. 1, 59-63). ASL and S413P ASL have been expressed, purified, and kinetically characterized. Lowering the Escherichia coli growth temperature to 25 degrees C and the concentration of inducer, isopropyl-1-thio-beta,D-galactopyranoside, to 40 microM was necessary for synthesis of soluble, tetrameric enzymes. The recombinant enzymes were purified to homogeneity using anion exchange chromatography followed by chromatography on Blue 2A Sepharose. At pH 7.0 and 25 degrees C, the kcat for cleavage of 5-amino-4-imidazole-N-succinocarboxamide ribotide (SAI-CAR) by ASL was 90 s-1 with a Km of 2.35 microM. The kcat for adenylosuccinate (SAMP) cleavage was 97 s-1 with a Km of 1.79 microM. The catalytic mechanism involved one general base catalyst (pK alpha = 6.4) and one general acid catalyst (pK alpha = 7.5). ASL follows an ordered uni-bi reaction mechanism with fumarate released first. 5-Amino-4-imidazolecarboxamide ribotide (AICAR) and AMP were competitive with SAICAR and SAMP (Ki[AICAR] = 11.3 microM; Ki[AMP] = 9.2 microM), whereas fumarate inhibited noncompetitively (Kii = 2.3 mM, Kis = 2.8 mM). The competitive inhibition by AICAR and AMP suggests a single active site that binds both SAICAR and SAMP. The kinetic constants at pH 7.0, 25 degrees C and the kcat/Km versus pH profiles for ASL and S413P ASL were very similar. These results are consistent with S413P being a structural rather than a catalytic defect.
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PMID:Expression, purification, and kinetic characterization of recombinant human adenylosuccinate lyase. 836 12

Adenylosuccinate lyase (ADSL; also called "adenylosuccinase") catalyzes two steps in the synthesis of purine nucleotides: (1) the conversion of succinylaminoimidazolecarboxamide ribotide into aminoimidazolecarboxamide ribotide and (2) the conversion of adenylosuccinate into adenosine monophosphate. ADSL deficiency, a recessively inherited disorder, causes variable-but most often severe-mental retardation, frequently accompanied by epilepsy and/or autism. It is characterized by the accumulation, in body fluids, of succinylaminoimidazolecarboxamide riboside and succinyladenosine, the dephosphorylated derivatives of the two substrates of the enzyme. Analysis of the ADSL gene of three unrelated patients with ADSL deficiency, in whom one of the ADSL alleles displayed a normal coding sequence, revealed a -49T-->C mutation in the 5' untranslated region of this allele. Measurements of the amount of mRNA transcribed from the latter allele showed that it was reduced to approximately 33% of that transcribed from the alleles mutated in their coding sequence. Further investigations showed that the -49T-->C mutation provokes a reduction to 25% of wild-type control of promoter function, as evaluated by luciferase activity and mRNA level in transfection experiments. The mutation also affects the binding of nuclear respiratory factor 2 (NRF-2), a known activator of transcription, as assessed by gel-shift studies. Our findings indicate that a mutation of a regulatory region of the ADSL gene might be an unusually frequent cause of ADSL deficiency, and they suggest a role for NRF-2 in the gene regulation of the purine biosynthetic pathway.
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PMID:Mutation of a nuclear respiratory factor 2 binding site in the 5' untranslated region of the ADSL gene in three patients with adenylosuccinate lyase deficiency. 1201 89

Adenylosuccinate lyase (ASL), a catalyst of key reactions in purine biosynthesis, is normally a homotetramer in which three subunits contribute to each of four active sites. Human ASL deficiency is an inherited metabolic disease associated with autism and mental retardation. We have characterized five disease-associated ASL mutants: R194C and K246E are located at subunit interfaces, L311V is in the central helical region away from the active site, and R396C and R396H are at the entrance to the active site. The V(max) (at 25 degrees C) for R194C is comparable to that of WT, while those of L311V, R396C, R396H, and K246E are considerably reduced and affinity for adenylosuccinate is retained. The mutant enzymes have decreased positive cooperativity as compared to WT. K246E exists mainly as dimer or monomer, accounting for its negligible activity, whereas the other mutant enzymes are similar to WT in the predominance of tetramer. At 37 degrees C, the specific activity of WT and these mutant enzymes slowly decreases 30-40% with time and reaches a limiting specific activity without changing significantly the amount of tetramer. Mutant R194C is unique in being rapidly inactivated at the harsher temperature of 60 degrees C, indicating that it is the least stable enzyme in vitro. Conformational changes in the mutant enzymes are evident from protein fluorescence intensity at 25 degrees C and after incubation at 37 degrees C, which correlates with the loss of enzymatic activity. Thus, these disease-associated single mutations can yield enzyme with reduced activity either by affecting the active site or by perturbing the enzyme's structure and/or native conformation which are required for catalytic function.
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PMID:Biochemical and biophysical analysis of five disease-associated human adenylosuccinate lyase mutants. 1940 74