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PubMed1987

Actinomycin synthetases. Multifunctional enzymes responsible for the synthesis of the peptide chains of actinomycin.

Two enzymes were purified from actinomycin-synthesizing Streptomyces chrysomallus which could be identified as peptide synthetases involved in the biosynthesis of actinomycin. Actinomycin synthetase II activates the first two amino acids of the peptide chains of the peptide lactone antibiotic, threonine and valine (or isoleucine), as thioesters via their corresponding adenylates. It is a single polypeptide chain of Mr 225,000. Similarly, actinomycin synthetase III activates proline, glycine, and valine (the remaining three amino acids in the antibiotic) as thioesters and is a single polypeptide chain of about Mr 280,000. It also carries the methyltransferase function(s) for N-methylation of thioesterified glycine and valine. In addition, it catalyzes the formation of cyclo(sarcosyl-N-methyl-L-valine) from glycine, L-valine, and S-adenosyl-L-methionine at the expense of ATP. Although the cell-free synthesis of the peptide lactone was not as yet accomplished, the data provide evidence that together with the 4-methyl-3-hydroxyanthranilic acid-activating enzyme (now designated as actinomycin synthetase I) all amino acid-activating protein components of the actinomycin-synthesizing enzyme complex are identified.

Amino Acids↗
PubMed1995

Low platelet mitochondrial complex I and complex II/III activity in early untreated Parkinson's disease.

Following the discovery of inhibition of electron transport complex 1 by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which produces a parkinsonian syndrome in humans, monkeys, and mice, several laboratories have reported abnormalities of complex I and other electron transport complexes (ETCs) in various tissues from patients with Parkinson's disease (PD). Criticism of the significance of these findings in the etiology of PD has centered on whether drug treatments or the debilitation of the disease process itself produced the low ETC activities. We present results from a blinded study of platelet mitochondrial ETC activities in 18 early untreated PD patients and 18 age- and sex-matched controls and in 13 spousal controls. Lower complex I activity in platelet mitochondria of PD patients was seen in early untreated disease and thus cannot be due to debilitation or drug therapy. Home environmental factors seem an unlikely explanation for the reduced complex I activity in PD patients but have not been excluded. Complex II/III activity was also reduced by 20% in PD compared with age-/sex-matched controls. The low complex I and II/III activities in platelet mitochondria appear to be related to the etiology of PD.

Adult↗
PubMed1988

Methotrexate: studies on the cellular metabolism. I. Effect on mitochondrial oxygen uptake and oxidative phosphorylation.

Effect of methotrexate (MTX) on mitochondrial oxygen uptake, oxidative phosphorylation and on the activity of several enzymes linked to respiratory chain was studied. MTX was able to inhibit state III respiration activated by ADP and to decrease the respiratory coefficient with the substrates alpha-ketoglutarate and glutamate; these effects became pronounced when mitochondria were pre-incubated with MTX for 10 min. No effect was observed on ATPase activity of undamaged or broken mitochondria; the same was true for NADH-oxidase, NADH-dehydrogenase, NADH-cytochrome c reductase, succinate oxidase, and cytochrome c oxidase activity. The effect on the steady-state of cytochrome b, as well as, the inhibitory effect on state III of respiration with NAD+-linked substrates, offers a reasonable possibility to suggesting that the inhibition site of MTX could be in a place anterior to cytochrome b region, and not linked to respiratory chain.

Adenosine Triphosphatases↗
PubMed2002

Etiopathogenesis and clinical presentation of carotid body tumors.

The carotid body (CB) is a highly specialized small organ located at the bifurcation of the common carotid artery in the neck and plays an important role in acute adaptation to hypoxia. The most common diseased state of the carotid body is its enlargement (i.e., the CB paraganglioma), which can be caused by a genetic predisposition (hereditary paraganglioma, PGL) and by chronic hypoxic stimulation. The CB is the most common tumor site in head and neck paragangliomas. Currently, inactivating germline mutations in the mitochondrial complex II subunits SDHB, SDHC, and SDHD have been identified as genetic risk factors for CB tumors (CBTs). Another locus at chromosome 11q13, identified by linkage analysis in a single family, may harbor a fourth susceptibility gene. Although CBTs are mostly slow-growing and benign, they can cause significant morbidity because of their proximity to major arteries and nerves in the head and neck. Here, we review the etiological factors implicated in the development of CBTs and provide information pertaining to their clinical presentation. Although CBTs are rare, they have the potential to provide unique insights for tumorigenesis and oxygen sensing and signaling mechanisms.

Carotid Body Tumor↗
PubMed1996

The effects of nitric oxide on electron transport complexes.

The effect of nitric oxide on mitochondrial electron transfer complexes was studied by comparing the activities of nitric oxide-treated and untreated, deoxygenated samples of purified beef heart succinate-cytochrome c reductase, succinate-ubiquinone reductase, and ubiquinol-cytochrome c reductase. More than 90% of succinate-cytochrome c reductase activity is lost during nitric oxide treatment. The activity of the succinate-ubiquinone reductase component of succinate-cytochrome c reductase decreases 95%, while the ubiquinol-cytochrome c reductase component is unaffected by nitric oxide. This inactivation is due primarily to the destruction of iron-sulfur clusters from succinate-ubiquinone reductase. When purified beef heart succinate-ubiquinone reductase was treated with nitric oxide, virtually all activity was irreversibly lost. The electron paramagnetic resonance (EPR) spectra of the treated complex showed typical iron-nitric oxide complex signals, confirming that inactivation is due to destruction of the iron-sulfur clusters. Similar results were obtained with purified Escherichia coli succinate-ubiquinone reductase. Pure beef heart ubiquinol-cytochrome c reductase treated with nitric oxide loses 40% of its initial activity, but regains most of it (90-100 % after 24 h of incubation at 0 degrees C in the absence of nitric oxide. This suggests that ubiquinol-cytochrome c reductase is protected from nitric oxide when complexed with succinate-ubiquinone reductase or that when split from succinate-ubiquinone reductase, ubiquinol-cytochrome c reductase undergoes a conformational change which allows access of nitric oxide to the Rieske iron-sulfur center. Such access is not possible when ubiquinol-cytochrome c reductase is complexed with succinate-ubiquinone reductase. The loss of ubiquinol-cytochrome c reductase activity correlates with a decrease in the Rieske protein EPR signal intensity without formation of any new EPR signal. The Rieske iron-sulfur cluster signal is recovered after 24 h incubation in the absence of nitric oxide.

Animals↗