Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.3.5.1 (succinate dehydrogenase)
 8,177 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We report the first case of a mitochondrial DNA (mtDNA) deletion diagnosed by renal biopsy. An eight-year-old girl with megaloblastic anemia and severe growth retardation developed progressive renal insufficiency accompanied by partial Fanconi syndrome. Histologic examination of the renal biopsy disclosed nonspecific chronic tubulointerstitial disease characterized by tubular atrophy and interstitial fibrosis. On ultrastructural examination, tubular cell mitochondria were extremely dysmorphic with prominent size variation, abnormal arborization, disorientation of the cristae and osmiophilic electron-dense inclusions. Functional histochemical stains for mitochondrial enzymes performed on cryostat renal sections revealed focal tubular absence of cytochrome C oxidase (COX), a respiratory chain enzyme partially encoded by mtDNA, with preservation of succinate dehydrogenase (SDH), a respiratory chain enzyme entirely encoded by nuclear DNA (nDNA). Immunoreactivity for COX subunit 2 (encoded by mtDNA) was weak to undetectable in most tubular cells, whereas reactivity for subunit 4 (encoded by nDNA) was intense in all cells. Molecular analysis of the mtDNA of kidney and peripheral blood leukocytes was performed using Southern blot and PCR. Both techniques disclosed a 2.7 kb mtDNA deletion located between nucleotide (nt) 9700 and nt 13700, a common site for mtDNA deletions associated with encephalomyopathies. Mitochondrial DNA deletions may be an under-recognized cause of idiopathic tubulointerstitial nephropathy in children lacking neurologic or myopathic manifestations.
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PMID:Mitochondrial DNA deletion: a cause of chronic tubulointerstitial nephropathy. 807 50

Methylmalonic acidemia (MMA) is a propionate pathway disorder caused by dysfunction of the mitochondrial enzyme methylmalonyl-CoA mutase (MMUT). MMUT catalyzes the conversion of methylmalonyl-CoA to succinyl-CoA, an anaplerotic reaction which feeds into the tricarboxylic acid (TCA) cycle. As part of the pathological mechanisms of MMA, previous studies have suggested there is decreased TCA activity due to a "toxic inhibition" of TCA cycle enzymes by MMA related metabolites, in addition to reduced anaplerosis. Here, we have utilized mitochondria isolated from livers of a mouse model of MMA (Mut-ko/ki) and their littermate controls (Ki/wt) to examine the amounts and enzyme functions of most of the TCA cycle enzymes. We have performed mRNA quantification, protein semi-quantitation, and enzyme activity quantification for TCA cycle enzymes in these samples. Expression profiling showed increased mRNA levels of fumarate hydratase in the Mut-ko/ki samples, which by contrast had reduced protein levels as detected by immunoblot, while all other mRNA levels were unaltered. Immunoblotting also revealed decreased protein levels of 2-oxoglutarate dehydrogenase and malate dehydrogenase 2. Interesting, the decreased protein amount of 2-oxoglutarate dehydrogenase was reflected in decreased activity for this enzyme while there is a trend towards decreased activity of fumarate hydratase and malate dehydrogenase 2. Citrate synthase, isocitrate dehydrogenase 2/3, succinyl-CoA synthase, and succinate dehydrogenase are not statistically different in terms of quantity of enzyme or activity. Finally, we found decreased activity when examining the function of methylmalonyl-CoA mutase in series with succinate synthase and succinate dehydrogenase in the Mut-ko/ki mice compared to their littermate controls, as expected. This study demonstrates decreased activity of certain TCA cycle enzymes and by corollary decreased TCA cycle function, but it supports decreased protein quantity rather than "toxic inhibition" as the underlying mechanism of action. SUMMARY: Methylmalonic acidemia (MMA) is an inborn metabolic disorder of propionate catabolism. In this disorder, toxic metabolites are considered to be the major pathogenic mechanism for acute and long-term complications. However, despite optimized therapies aimed at reducing metabolite levels, patients continue to suffer from late complications, including metabolic stroke and renal insufficiency. Since the propionate pathway feeds into the tricarboxylic acid (TCA) cycle, we investigated TCA cycle function in a constitutive MMA mouse model. We demonstrated decreased amounts of the TCA enzymes, Mdh2 and Ogdh as semi-quantified by immunoblot. Enzymatic activity of Ogdh is also decreased in the MMA mouse model compared to controls. Thus, when the enzyme amounts are decreased, we see the enzymatic activity also decreased to a similar extent for Ogdh. Further studies to elucidate the structural and/or functional links between the TCA cycle and propionate pathways might lead to new treatment approaches for MMA patients.
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PMID:Tricarboxylic acid cycle enzyme activities in a mouse model of methylmalonic aciduria. 3164 43