Considerable information on the intracellular localization of enzymes has been obtained in recent years through the technique of differential centrifugation of sucrose homogenates of tissues and subsequent testing of the fractions for enzyme activity. One of the results of this work has been the demonstration that rat liver mitochondria (Mw) are capable of completely oxidizing a wide variety of...

When a number of metal ions were tested as activators over a lOO-fold range of metal ion concentration (0.01 to 1.0 mM), aconitase was specifically activated by Fe(II). Manganese(I1) does not activate aconitase but binds to the enzyme, as shown indirectly by inhibition of the enzyme activation by Fe(I1) and directly by electron paramagnetic resonance. A titration of the enzyme with Mn(I1) may b...

Bleomycin (BLM) is a useful anticancer agent sometimes associated with a diffuse pulmonary inflammation and fibrosis. Using an intratracheal model of BLM-induced pulmonary damage, we have further investigated alveolar macrophage (AM) activation following intratracheal BLM. From rats that had been treated with either a single, fibrogenic, intratracheal dose of BLM (BLM-AM) or a comparable volume...

Although aluminum is known to be toxic to most organisms, its precise biochemical interactions are not fully understood. In the present study, we demonstrate that aluminum promotes the inhibition of aconitase (Acn) activity via the perturbation of the Fe-S cluster in Pseudomonas fluorescens. Despite the significant decrease in citrate isomerization activity, cellular survival is assured by the ...

Iron-responsive element-binding proteins (IRE-BPs) are cytosolic proteins that bind to a conserved RNA stem-loop, termed the iron-responsive element (IRE), that is located in the 5'- or 3'-untranslated regions of mRNAs involved in iron metabolism. Binding of the IRE-BP to 5'-IREs represses translation, whereas binding to 3'-IREs stabilizes the mRNA. The previously identified IRE-BP (BP1) contai...

Zinc is an essential metal for all organisms, as it participates in the structure and/or function of many proteins. However, zinc excess is as deleterious to cells as zinc deficiency. A genome-wide study of the transcriptomic response to high zinc in S. cerevisiae performed in our laboratory allowed the identification of a zinc hyper-tolerant deletion mutant (pif1Δ), which lacks the Pif1 DNA he...

The capacity of readily exchanging electrons makes iron not only essential for fundamental cell functions, but also a potential catalyst for chemical reactions involving free-radical formation and subsequent oxidative stress and cell damage. Cellular iron levels are therefore carefully regulated in order to maintain an adequate substrate while also minimizing the pool of potentially toxic 'free...

Expression of several proteins of higher eukaryotes is post-transcriptionally regulated by interaction of iron-responsive elements (IREs) on their mRNAs and iron regulatory proteins (IRP1 and IRP2). IRP1 is a redox-sensitive iron-sulfur protein whose regulatory activity is modulated by iron depletion, synthesis of nitric oxide, or oxidative stress. IRP2 is closely related to IRP1, but it does n...

The Saccharomyces cerevisiae Tmt1 gene product is the yeast homologue of the Escherichia coli enzyme that catalyzes the methyl esterification of trans-aconitate, a thermodynamically favored isomer of cis-aconitate and an inhibitor of the citric acid cycle. It has been proposed that methylation may attenuate trans-aconitate inhibition of aconitase and other enzymes of the cycle. Although trans-a...