The trans-aconitate methyltransferase from the bacterium Escherichia coli catalyzes the monomethyl esterification of trans-aconitate and related compounds. Using two-dimensional (1)H/(13)C nuclear magnetic resonance spectroscopy, we show that the methylation is specific to one of the three carboxyl groups and further demonstrate that the product is the 6-methyl ester of trans-aconitate (E-3-car...

Five experiments that support this scheme are presented. 1. The conversion of 3-T-isocitrate to citrate at early times gives T-citrate with no loss of tritium. 2. When the conversion of 2-T-citrate to isocitrate is brought to completion by trapping the isocitrate with isocitrate dehydrogenase, and the oc-ketoglutarate formed with glutamate dehydrogenase, the amount of tritium found in the gluta...

Friedreich ataxia (FRDA) results from a generalized deficiency of mitochondrial and cytosolic iron-sulfur protein activity initially ascribed to mitochondrial iron overload. Recent in vitro data suggest that frataxin is necessary for iron incorporation in Fe-S cluster (ISC) and heme biosynthesis. In addition, several reports suggest that continuous oxidative damage resulting from hampered super...

Recently, we observed that Staphylococcus aureus strains newly isolated from patients had twofold-higher aconitase activity than a strain passaged extensively in vitro, leading us to hypothesize that aconitase specific activity decreases over time during in vitro passage. To test this hypothesis, a strain recovered from a patient with toxic shock syndrome was serially passaged for 6 weeks, and ...

Peroxisomes produce hydrogen peroxide as a metabolic by-product of their many oxidase enzymes, but contain catalase that breaks down hydrogen peroxide in order to maintain the organelle's oxidative balance. It has been previously demonstrated that, as cells age, catalase is increasingly absent from the peroxisome, and resides instead as an unimported tetrameric molecule in the cell cytosol; an ...

The aconitase protein of Bacillus subtilis was able to bind specifically to sequences resembling the iron response elements (IREs) found in eukaryotic mRNAs. The sequences bound include the rabbit ferritin IRE and IRE-like sequences in the B. subtilis operons that encode the major cytochrome oxidase and an iron uptake system. IRE binding activity was affected by the availability of iron both in...

Several mechanisms of posttranscriptional gene regulation are involved in regulation of the expression of essential proteins of iron metabolism. Coordinate regulation of ferritin and transferrin receptor expression is produced by binding of a cytosolic protein, the iron-responsive element binding protein (IRE-BP) to specific stem-loop structures present in target RNAs. The affinity of this prot...

Aconitase, which catalyses the conversion of citrate into isocitrate, requires Fe for its activity. The yeast and animal enzyme loses its enzymatic activity under Fe shortage and binds to RNA of genes involved in Fe homeostasis, altering their expression. Thus, the enzyme provides a regulatory link between organic acid metabolism and Fe cellular status. Roots and leaves of Fe-deficient plants s...

Considering membranes and membrane components as possible pacemakers of the main processes taking place inside mitochondria, changes in phospholipids or fatty acids could play a central role linking different mechanisms involved in cumulative damage to cell molecules and dysfunction during periods of high stress, such as rapid growth and aging. Changes affecting either lipid class or fatty acid...

In its aconitase-inactive form, IRP-1 (iron regulatory protein-1)/cytosolic aconitase binds to the IRE (iron-responsive element) of several mRNAs to effect post-transcriptional regulation. We have shown previously that IRP-1 has ATPase activity and that binding of ATP suppresses the IRP-1/IRE interaction. In the present study, we characterize the binding activity further. Binding is observed wi...