Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0020500 (hyperoxaluria)
 912 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We examine the suitability of a rapid and sensitive liquid chromatographic technique to determine L-alanine:glyoxylate aminotransferase (AGT) activity in human liver. Homogenised tissue was incubated for 30 min in the presence of substrates and the generated pyruvate was converted into the corresponding phenylhydrazone which was determined using reversed-phase high-performance liquid chromatography (HPLC). The procedure allowed the detection of the enzyme activity expressed by 10 micrograms of liver protein and was rapid enough resulting more sensitive and less time-consuming than the previous colorimetric one. We found that AGT activity in two hyperoxaluria type 1 patients was reduced as compared with controls. Also, cirrhotic patients had very low enzyme activities, even in the absence of detectable disorders of oxalate metabolism and this was ascribed to abnormal liver morphology. This may represent a misleading drawback if diagnosis of type 1 primary hyperoxaluria (PH1) uniquely relies on AGT assay.
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PMID:High-performance liquid chromatographic microassay for L-alanine:glyoxylate aminotransferase activity in human liver. 149 37

In approximately one-third of primary hyperoxaluria type 1 patients, disease is associated with a unique protein sorting defect in which hepatic L-alanine:glyoxylate aminotransferase (AGT; EC 2.6.1.44), which is normally peroxisomal, is mistargeted to mitochondria. In all such patients analyzed to date, the gene encoding the aberrantly targeted AGT carries three point mutations, each of which specifies an amino acid substitution. In this paper we show that one of these substitutions, a proline-to-leucine at residue 11, is necessary and sufficient for the generation of a mitochondrial targeting sequence in the AGT protein. AGT with this substitution appears to interact specifically with the mitochondrial protein import machinery, via a discrete N-terminal domain of the AGT protein. The N-terminal 19 amino acids of AGT with this substitution are sufficient to direct mouse cytosolic dihydrofolate reductase to mitochondria, and a synthetic peptide corresponding to this same 19-amino acid region reversibly inhibits mitochondrial protein import, not only of AGT but also of ornithine transcarbamoylase, a genuine cytoplasmically synthesized mitochondrial protein. We have extended these studies to analyze a region of normal human AGT cDNA directly upstream of the coding region. This sequence appears to correspond to an ancestral mitochondrial targeting sequence deleted from the human coding region by point mutation at the initiation codon. We show that reestablishment of this initiation codon produces an active mitochondrial targeting sequence that is different to that found in the hyperoxaluria patients. These results are discussed with reference to the AGT targeting defect in primary hyperoxaluria and also in relation to the highly unusual species specificity of subcellular distribution of AGT among mammals.
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PMID:Mistargeting of peroxisomal L-alanine:glyoxylate aminotransferase to mitochondria in primary hyperoxaluria patients depends upon activation of a cryptic mitochondrial targeting sequence by a point mutation. 196 59