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PubMed1987

Involvement of a carboxyl group in the interaction between succinate dehydrogenase and its membrane-anchoring protein (QPs) fraction.

The involvement of the carboxyl groups in the membrane-anchoring protein (QPs) in reconstitution of succinate dehydrogenase to form succinate-ubiquinone reductase is studied by using a carboxyl group modifying reagent, dicyclohexylcarbodiimide (DCCD). Inactivation of QPs by DCCD is found to be dependent on the temperature, pH, detergent, and DCCD concentration used. When QPs is treated with 300 molar excess DCCD at room temperature for 10 min, about 90% of the original reconstitutive activity is lost. When intact or reconstituted succinate-ubiquinone reductase formed from reconstitutively active succinate dehydrogenase and QPs is treated with DCCD under the same conditions, no loss of succinate-ubiquinone reductase activity is observed. However, when a mixture of reconstitutively inactive succinate dehydrogenase and QPs is treated with DCCD before being reconstituted with active succinate dehydrogenase, an inactivation behavior similar to that with QPs alone is observed. These results indicate that DCCD modifies the carboxyl groups of QPs which are essential for the interaction with succinate dehydrogenase to form succinate-ubiquinone reductase. Inactivation of QPs by DCCD parallels the incorporation of DCCD into QPs. About two carboxyl groups per molecule of QPs are essential for the interaction with succinate dehydrogenase. These essential carboxyl groups are located in the smaller subunit (Mr 13,000) of QPs. Modification of QPs by DCCD also alters the heme environment of cytochrome b560.

Dicyclohexylcarbodiimide↗

PubMed2005

Activation of isolated NADH:ubiquinone reductase I (complex I) from Escherichia coli by detergent and phospholipids. Recovery of ubiquinone reductase activity and changes in EPR signals of iron-sulfur clusters.

NADH:ubiquinone oxidoreductase (NDH-1 or complex I) from Escherichia coli was purified using a combination of anion exchange chromatography and centrifugation in sucrose density gradient. The dependence of enzyme activity on detergent and phospholipids was studied. Artificial hexaammineruthenium reductase activity was not affected by dodecyl maltoside (DDM) and asolectin. Ubiquinone reductase activity had a bell-shape dependence on DDM concentration; 7-10-fold activation could be achieved. Treatment with asolectin subsequently yields additional 2-fold activation with a corresponding increase in the apparent V(max) and without significant changes in apparent K(m). Comparative EPR studies of complex I reduced with NADH, "as prepared" and "activated by asolectin" showed an increase in the signals derived mainly from two [4Fe-4S] clusters in the activated enzyme. One of these signals could be simulated with an axial spectrum with g values of g(xyz)= 1.895, 1.904, 2.05, which corresponds to the parameters reported for the N2 cluster. This data indicates conformational rearrangements of catalytic importance in complex I upon binding of phospholipids.

Detergents↗

PubMed2001

The carboxin-binding site on Paracoccus denitrificans succinate:quinone reductase identified by mutations.

Succinate:quinone reductase catalyzes electron transfer from succinate to quinone in aerobic respiration. Carboxin is a specific inhibitor of this enzyme from several different organisms. We have isolated mutant strains of the bacterium Paracoccus denitrificans that are resistant to carboxin due to mutations in the succinate:quinone reductase. The mutations identify two amino acid residues, His228 in SdhB and Asp89 in SdhD, that most likely constitute part of a carboxin-binding site. This site is in the same region of the enzyme as the proposed active site for ubiquinone reduction. From the combined mutant data and structural information derived from Escherichia coli and Wolinella succinogenes quinol:fumarate reductase, we suggest that carboxin acts by blocking binding of ubiquinone to the active site. The block would be either by direct exclusion of ubiquinone from the active site or by occlusion of a pore that leads to the active site.

Amino Acid Sequence↗

PubMed2000

Mutations in SDHC cause autosomal dominant paraganglioma, type 3.

Nonchromaffin paragangliomas (PGLs) are usually benign, neural-crest-derived, slow-growing tumours of parasympathetic ganglia. Between 10% and 50% of cases are familial and are transmitted as autosomal dominant traits with incomplete and age-dependent penetrance.

Chromosomes, Human, Pair 1↗

PubMed2003

A role for mitochondrial enzymes in inherited neoplasia and beyond.

Mitochondrial defects have been associated with neurological disorders, as well as cancers. Two ubiquitously expressed mitochondrial enzymes--succinate dehydrogenase (SDH) and fumarate hydratase (FH, fumarase)--catalyse sequential steps in the Krebs tricarboxylic-acid cycle. Inherited heterozygous mutations in the genes encoding these enzymes cause predispositions to two types of inherited neoplasia syndromes that do not share any component tumours. Homozygous mutations in the same genes result in severe neurological impairment. Understanding this link between inherited cancer syndromes and neurological disease could provide further insights into the mechanisms by which mitochondrial deficiencies lead to tumour development.

Apoptosis↗

PubMed2002

Identification of novel SDHD mutations in patients with phaeochromocytoma and/or paraganglioma.

Familial paraganglioma is a dominantly inherited disorder characterised by the development of highly vascular tumours in the head and neck. Recently, a relationship between hereditary tumours derived from the autonomic nervous system and germline mutations in the gene encoding succinate dehydrogenase complex subunit D (SDHD) is increasingly a subject of study. Familial paraganglioma syndrome is embryologically related to phaeochromocytoma, another neuroendocrine tumour that shows great aetiological and genetic heterogeneity. Some hereditary phaeochromocytomas may be associated with germline mutations in VHL, RET and NF1 genes in genetic disorders such as von Hippel-Lindau disease (VHL), multiple endocrine neoplasia type 2 (MEN 2) and neurofibromatosis type 1 (NF 1), respectively. However, there are many cases that cannot be explained by mutations in these genes. In this report, we describe two previously unreported mutations in two patients from 25 unrelated kindreds with phaeochromocytoma and/or paraganglioma disorders and with or without familial antecedents: a mutation featuring the change of tryptophan to a termination codon in exon 2, and a 4-bp deletion in exon 4 that results in a truncated protein. We also describe one missense substitution of uncertain significance. The patients had previously tested negative for germline mutations in VHL and RET genes and had not been previously selected. The involvement of SDHD mutations in familial phaeochromocytoma and/or paraganglioma predisposition is of considerable interest since other studies have shown these alterations to be associated with highly expressed angiogenic factors.

Adrenal Gland Neoplasms↗

PubMed2001

Germline SDHD mutation in paraganglioma of the spinal cord.

Hereditary paraganglioma of the head and neck is associated with germline mutations in the SDHD gene, which encodes a mitochondrial respiratory chain protein. Paragangliomas of the central nervous system are very rare, occur almost exclusively in the cauda equina of the spinal cord and are considered non-familial. In the present study, we screened 22 apparently sporadic paragangliomas of the cauda equina for SDHD mutations. One spinal paraganglioma and similar cerebellar tumours that developed 22 years later in the same patient contained a missense mutation at codon 12 (GGT-->AGT, Gly-->Ser) and a silent mutation at codon 68 (AGC-->AGT, Ser-->Ser). There was no family history of paragangliomas but DNA from white blood cells of this patient showed the same sequence alterations, indicating the presence of a germline mutation. All other cases of spinal paraganglioma had the wild-type SDHD sequence, except one case with a silent mutation at codon 68 (AGC-->AGT, Ser-->Ser). This is the first observation indicating that inherited SDHD mutations may occasionally cause the development of paragangliomas in the central nervous system.

Cauda Equina↗

PubMed1949