Nature of non-transferrin-bound iron: studies on iron citrate complexes and thalassemic sera

Despite its importance in iron-overload diseases, little is known about the composition of plasma non-transferrin-bound iron (NTBI). Using 30-kDa ultrafiltration, plasma from thalassemic patients consisted of both filterable and non-filterable NTBI, the filterable fraction representing less than 10% NTBI. Low filterability could result from protein binding or NTBI species exceeding 30 kDa. The properties of iron citrate and its interaction with albumin were therefore investigated, as these represent likely NTBI species. Iron permeated 5- or 12-kDa ultrafiltration units completely when complexes were freshly prepared and citrate exceeded iron by tenfold, whereas with 30-kDa ultrafiltration units, permeation approached 100% at all molar ratios. A g = 4.3 electron paramagnetic resonance signal, characteristic of mononuclear iron, was detectable only with iron-to-citrate ratios above 1:100. The ability of both desferrioxamine and 1,2-dimethyl-3-hydroxypyridin-4-one to chelate iron in iron citrate complexes also increased with increasing ratios of citrate to iron. Incremental molar excesses of citrate thus favour the progressive appearance of chelatable lower molecular weight iron oligomers, dimers and ultimately monomers. Filtration of iron citrate in the presence of albumin showed substantial binding to albumin across a wide range of iron-to-citrate ratios and also increased accessibility of iron to chelators, reflecting a shift towards smaller oligomeric species. However, in vitro experiments using immunodepletion or absorption of albumin to Cibacron blue–Sepharose indicate that iron is only loosely bound in iron citrate–albumin complexes and that NTBI is unlikely to be albumin-bound to any significant extent in thalassemic sera.     

Biochemical and spectroscopic studies of human melanotransferrin (MTf): electron-paramagnetic resonance evidence for a difference between the iron-binding site of MTf and other transferrins

Melanotransferrin (MTf) is a member of the transferrin (Tf) family of iron (Fe)-binding proteins that was first identified as a cell-surface marker of melanoma. Although MTf has a high-affinity Fe-binding site that is practically identical to that of serum Tf, the protein does not play an essential role in Fe homeostasis and its precise molecular function remains unclear. A Zn(II)-binding motif, distinct from the Fe-binding site, has been proposed in human MTf based on computer modelling studies. However, little is known concerning the interaction of its proposed binding site(s) with metals and the consequences in terms of MTf conformation. For the first time, biochemical and spectroscopic techniques have been used in this study to characterise metal ion-binding to recombinant MTf. Initially, the binding of Fe to MTf was examined using 6M urea gel electrophoresis. Although four different iron-loaded forms were observed with serum Tf, only two forms were found with MTf, the apo-form and the N-monoferric holo-protein, suggesting a single high-affinity site. The presence of a single Fe(III)-binding site was also supported by EPR results which indicated that the Fe(III)-binding characteristics of MTf were unique, but somewhat comparable to the N-lobes of human serum Tf and chicken ovo-Tf. Circular dichroism (CD) analysis indicated that, as for Tf, no changes in secondary structure could be observed upon Fe(III)-binding. The ability of MTf to bind Zn(II) was also investigated using CD which demonstrated that the single high-affinity Fe-binding site was distinct from a potential Zn(II)-binding site.     

BAmSA: Visualising transmembrane regions in protein complexes using biotinylated amphipols and electron microscopy

Membrane protein (MP) complexes play key roles in all living cells. Their structural characterisation is hampered by difficulties in purifying and crystallising them. Recent progress in electron microscopy (EM) have revolutionised the field, not only by providing higher-resolution structures for previously characterised MPs but also by yielding first glimpses into the structure of larger and more challenging complexes, such as bacterial secretion systems. However, the resolution of pioneering EM structures may be difficult and their interpretation requires clues regarding the overall organisation of the complexes. In this context, we present BAmSA, a new method for localising transmembrane (TM) regions in MP complexes, using a general procedure that allows tagging them without resorting to neither genetic nor chemical modification. Labels bound to TM regions can be visualised directly on raw negative-stain EM images, on class averages, or on three-dimensional reconstructions, providing a novel strategy to explore the organisation of MP complexes.     

Effects of dopaminergic drugs on the concentrations of PGE2 and PGF2alpha in various brain regions

It has long been shown by Biggio and Guidotti that multisynaptic nigro-cerebellar pathway of dopaminergic origin can control cerebellar cyclic guanosinmonophosphate (cGMP) content, a good index of the activity of Purkinje cells. In this line, it has been reported that haloperidol and sulpiride, significantly decrease cerebellar cGMP content while opposite changes are observed with apomorphine. In an attempt to establish whether other cerebellar cGMP-related parameters may be influenced by dopamine drugs. Authors have investigated the effects of haloperidol, sulpiride and apomorphine on cerebellar PGE2 and PGF2alpha. Results obtained indicate that haloperidol and sulpiride significantly reduce cerebellar PGE2 and PGF2alpha content while opposite changes are induced by apomorphine. Similar results have been observed in substantia nigra but not in other brain regions, such as corpus striatum and medial basal hypothalamus. The possibility that the observed changes in cerebellar PG-content may result from the modulation of striatal dopamine receptors is discussed.     

Contribution of Gluconacetobacter diazotrophicus to phosphorus nutrition in strawberry plants

Plant and Soil - Gluconacetobacter diazotrophicus (family Acetobacteraceae), is a N2-fixing bacterium with capability of mineral solubilization through organic acid production. The aim of this work...     

Fatty acid composition of the seed lipids of Chamaerops humilis L. natural populations and its relation with the environment

Seed lipids composition is a tool to discriminate among plant taxa and is related to phylogeny and biogeographic distribution. Aim of the present study was to evaluate the fatty acid (FA) composition of the seed lipids from nine natural Chamaerops humilis L. population and its relation with the climatic traits of the collection sites. The average seed lipids content was 54.8 g kg^? 1 and the most represented FAs were oleic (478 g kg^? 1 oil) and linoleic (230 g kg^? 1 oil), with significant differences among the accessions. Most of the lipid traits significantly correlated with climatic traits. In particular, oleic acid negatively correlated with year potential evapotranspiration. These relations could emerge from a genotypic adaptation to the environment. The seed of C. humilis showed high content of lipids, which implies an importance of the species for feeding wild life during winter, and a high degree of unsaturation. Considering the importance of the unsaturated FAs in human and animal nutrition, the present results suggest that European fan palm could be introduced in breeding programmes and its seed extract used as FA in diet supplementation. Further studies are needed to identify the content of anti-nutritional or nutraceutical compounds.