Iron, Transferrin, and Ferritin in the Rat Brain During Development and Aging

Abstract: Iron is a universal cofactor for mitochondrial energy generation and supports the growth and differentiation of all cell types. In the CNS, iron is a key component of systems responsible for myelination and the synthesis of several neurotransmitters. In this study the spatial and temporal pattern of iron and its regulatory proteins transferrin and ferritin are quantitatively examined in the rat CNS during the first 3 weeks of postnatal life and in adults and aged animals. The midbrain, the cerebral cortex, and the cerebellum-pons are examined independently. Iron, transferrin, and ferritin concentrations are highest in all three brain regions at birth and decrease in each region to minimum levels during the third postnatal week. The decrease in levels of iron, transferrin, and ferritin is most pronounced in the cerebellum-pons and cortex and least in the midbrain. From postnatal day 17, iron (total iron content) and ferritin levels increase throughout the lifetime of the rat. In contrast, transferrin levels remain fairly constant in each brain region after postnatal day 24. The midbrain region, which includes the iron-rich regions such as the globus pallidus, substantia nigra, and red nucleus, has the least change in iron with development, has the highest level of ferritin during development, and consistently has the highest level of transferrin at all ages. These observations are consistent with reports that iron is important for normal motor function. Transferrin did not increase after postnatal day 24 in the three brain regions examined despite increasing amounts of iron, which implies a decrease in iron mobility in the aged rats, a finding that is consistent with observations of human brain tissue. The data reported in this study demonstrate that iron acquisition and mobilization systems in the CNS are established early in development and that the overall pattern of acquisition among brain regions is similar. These data offer support and insight into established concepts that a sufficient iron supply is critical for normal neurological development.     

Cloning of the nupC gene of Escherichia coli encoding a nucleoside transport system, and identification of an adjacent Insertion element, IS 186

Escherichia coli is known to contain more than one active transport system for nucleoside uptake. In the present study we report the sequence of a gene encoding a second nucleoside transport system, nupC (in addition to nupG.) An open reading frame (ORF) of 1200bp was identified that codes for a hydrophobic polypeptide of 43 560 Da and an NupC fusion protein was shown to be membrane associated. The native NupC protein is also identified, following over-expression. NupC exhibits short regions of homology to several membrane-associated proteins, including LacY and Cyd. Analysis of the nupC promoter region revealed the presence of at least two putative CRP-binding sites, centred at–40bp and–89bp, which probably flank a CytR-binding site. In addition, an adjacent IS186 element was identified and found to reside within a putative terminator structure, downstream from the nupC ORF. This arrangement is shown to reflect the previously established gene order on the E. coli chromosome.     

The effect of methyl palmoxirate on incorporation of [U-14C]palmitate into rat brain

We examined the dose response, time course and reversibility of the effect of methyl 2-tetradecylglycidate (McN-3716, methyl palmoxirate or MEP), an inhibitor of -oxidation of fatty acids, on incorporation of radiolabeled palmitic acid ([U-¹⁴C]PA) from plasma into brain lipids of awake rats. MEP (0.1, 1 and 10 mg/kg) or vehicle was administered intravenously from 10 min to 72 hr prior to infusion of [U-¹⁴C]PA. Two hr pretreatment with MEP (0.1 to 10 mg/kg) increased brain organic radioactivity 1.2 to 1.8 fold and decreased brain aqueous radioactivity by 1.2 to 3.0 fold when compared to control values. At 10 mg/kg, MEP significantly increased brain organic fraction from 40% in controls to 85%, 30 min to 6 hr pretreatment, and resulted in a redistribution of the radiolabeled fatty acid toward triacylglycerol. MEP changed the lipid/aqueous brain ratio of incorporated [U-¹⁴C]PA from 0.67 to 5.7. The incorporation rate coefficient, k^*, was significantly increased by MEP (10 mg/kg) at 2 hr (31%), 4 hr (59%) and 6 hr (34%). All effects were reversed by 72 hr, consistent with a half-life of 2 days for carnitine palmitoyl transferase I. These results indicate that intravenous MEP may be used with [1-¹¹C]palmitic acid for studying brain lipid metabolism in vivo by positron emission tomography, as it significantly reduces the large unincorporated aqueous fraction that would result in high background radioactivity.     

Effect of disulfide bridge formation on the NMR spectrum of a protein: Studies on oxidized and reduced Escherichia coli thioredoxin

Summary As a prelude to complete structure calculations of both the oxidized and reduced forms of Escherchia coli thioredoxin (M_r 11 700), we have analyzed the NMR data obtained for the two proteins under identical conditions. The complete aliphatic ¹³C assignments for both oxidized and reduced thioredoxin are reported. Correlations previously noted between ¹³C chemical shifts and secondary structure are confirmed in this work, and significant differences are observed in the C and C shifts between cis- and trans-proline, consistent with previous work that identifies this as a simple and unambiguous method of identifying cis-proline residues in proteins. Reduction of the disulfide bond in the active-site Cys³²-Gly-Pro-Cys³⁵ sequence causes changes in the ¹H, ¹⁵N and ¹³C chemical shifts of residues close to the active site, some of them quite far distant in the amino acid sequence. Coupling constants, both backbone and side chain, show some differences between the two proteins, and the NOE connectivities and chemical shifts are consistent with small changes in the positions of several side chains, including the two tryptophan rings (Trp²⁸ and Trp³¹). These results show that, consistent with the biochemical behavior of thioredoxin, there are minimal differences in backbone configuration between the oxidized and reduced forms of the protein.     

Phosphorylation of Rat Brain Choline Acetyltransferase and Its Relationship to Enzyme Activity

Abstract— Choline acetyltransferase catalyzes the formation of acetylcholine from choline and acetyl-CoA in cholin-ergic neurons. The present study examined conditions for modulation of kinase-mediated phosphorylation of this enzyme. By using a monospecific polyclonal rabbit anti-human choline acetyltransferase antibody to immunoprecipi-tate cytosolic and membrane-associated subcellular pools of enzyme from rat hippocampal synaptosomes, we determined that only the cytosolic fraction of the enzyme (67,000 ± 730 daltons) was phosphorylated under basal, unstimulated conditions. The quantity of this endogenous phosphoprotein was dependent, in part, upon the level of intracellular calcium, with ³²P_i incorporation into the enzyme in nerve terminals incubated in nominally calcium-free medium only 43 ± 7% of control. The corresponding enzymatic activity of cytosolic choline acetyltransferase did not appear to be altered by lowered cytosolic calcium, whereas membrane-associated choline acetyltransferase activity was decreased to 58 ± 11 % of control. Depolarization of synaptosomes with 50 μ M veratridine neither altered the extent of phosphorylation or specific activity of cytosolic choline acetyltransferase, nor induced detectable phosphorylation of membrane-associated choline acetyltransferase, although the specific activity of the membrane-associated enzyme was increased to 132 ± 5% of control. In summary, phosphorylation of choline acetyltransferase does not appear to regulate cholinergic neurotransmission by a direct action on catalytic activity of the enzyme.     

Nonenzymatic Glycosylation of Lepidopteran-Active Bacillus thuringiensis Protein Crystals

We used high-pH anion-exchange chromatography with pulsed amperometric detection to quantify the monosaccharides covalently attached to Bacillus thuringiensis HD-1 (Dipel) crystals. The crystals contained 0.54% sugars, including, in decreasing order of prevalence, glucose, fucose, arabinose/rhamnose, galactose, galactosamine, glucosamine, xylose, and mannose. Three lines of evidence indicated that these sugars arose from nonenzymatic glycosylation: (i) the sugars could not be removed by N- or O-glycanases; (ii) the sugars attached were influenced both by the medium in which the bacteria had been grown and by the time at which the crystals were harvested; and (iii) the chemical identity and stoichiometry of the sugars detected did not fit any known glycoprotein models. Thus, the sugars detected were the product of fermentation conditions rather than bacterial genetics. The implications of these findings are discussed in terms of crystal chemistry, fermentation technology, and the efficacy of B. thuringiensis as a microbial insecticide.     

Atrial natriuretic peptide binding in rat placenta,yolk sac,decidua, and materal placental vessels

Using in vitro autoradiography, binding sites of ¹²⁵I-ANP (atrial natriuretic peptide) were localized in the rat placenta, visceral yolk sac, and decidua at 16, 18, and 20 days of gestation. There was diffuse binding over the labyrinthine region of the placenta and an intense binding over the decidual gland and visceral yolk sac. In the yolk sac, ANP localized over the cores of the villi where it may be involved with the regulation of transport across the membranes or the flow of blood through the vitelline vessels. Of particular interest was binding over the maternal blood vessels supplying the decidual region and placenta. Receptors were located on the endothelial cells and smooth muscle cells of the arteries and veins, indicating that ANP may be involved with regional regulation of blood flow to the placenta.