Manganese stimulates luteinizing hormone releasing hormone secretion in prepubertal female rats: hypothalamic site and mechanism of action.

We have shown recently that Mn2+ stimulates gonadotropin secretion via an action at the hypothalamic level, and a diet supplemented with a low dose of the element is capable of advancing the time of female puberty. In this study, we used an in vitro approach to investigate the mechanism by which Mn2+ induces luteinizing hormone-releasing hormone (LHRH) secretion from prepubertal female rats. The medial basal hypothalamus from 30-day-old rats was incubated in Locke solution for 30 min to assess basal LHRH secretion, then incubated with buffer alone or buffer plus either a nitric oxide synthase (NOS) inhibitor (N-monomethyl-L-arginine (NMMA); 300 or 500 microM) or a soluble guanylyl cyclase (sGC) inhibitor (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ); 100 or 250 microM) for another 30 min. Finally, the incubation continued for a further 30 min, but in the presence of MnCl2 (50 or 250 microM) to assess the effect of the blockers on stimulated LHRH secretion. Both 50 and 250 microM MnCl2 stimulated LHRH release (P < 0.05 and P < 0.01, respectively). The addition of 300-500 microM NMMA to the medium did not block Mn2+-stimulated release of LHRH, even with the higher dose of MnCl2. Furthermore, while 50, 100 and 250 microM MnCl2 all significantly induced LHRH release, the two lowest doses did not stimulate total nitrite released from the same tissue, an effect only observed with the highest dose. Taken together, these data suggest that Mn2+ is not an effective stimulator of NO. Conversely, inhibiting sGC with ODQ blocked the Mn2+-stimulated secretion of LHRH in a dose-dependent manner, indicating that GC is the site of action of Mn2+. Additionally, we showed that Mn2+ stimulated cGMP and LHRH from the same tissues, and that downstream blocking of protein kinase G formation with KT5823 (10 microM) inhibited Mn2+-induced LHRH release. These data demonstrate that the principal action of Mn2+ within the hypothalamus is to activate sGC directly and/or as a cofactor with available NO, hence generating cGMP and resulting in prepubertal LHRH release.

Manganese is the link between frataxin and iron-sulfur deficiency in the yeast model of Friedreich ataxia.

Friedreich ataxia is a human neurodegenerative and myocardial disease caused by decreased expression of the mitochondrial protein frataxin. Proteomic analysis of the mutant yeast model of Friedreich ataxia presented in this paper reveals that these cells display increased amounts of proteins involved in antioxidant defenses, including manganese-superoxide dismutase. This enzyme shows, however, lower activity than that found in wild type cells. Our results indicate that this lack of activity is a consequence of cellular manganese deficiency, because in manganese-supplemented cultures, cell manganese content, and manganese-superoxide dismutase activity were restored. One of the hallmarks of Friedreich ataxia is the decreased activity of iron/sulfur-containing enzymes. The activities of four enzymes of this group (aconitase, glutamate synthase, succinate dehydrogenase, and isopropylmalate dehydratase) have been analyzed for the effects of manganese supplementation. Enzyme activities were recovered by manganese treatment, except for aconitase, for which, a specific interaction with frataxin has been demonstrated previously. Similar results were obtained when cells were grown in iron-limited media suggesting that manganese-superoxide dismutase deficiency is a consequence of iron overload. In conclusion, these data indicate that generalized deficiency of iron-sulfur protein activity could be a consequence of manganese-superoxide dismutase deficiency, and consequently, it opens new strategies for Friedreich ataxia treatment.

Manganese-dependent regulation of the endocarditis-associated virulence factor EfaA of Enterococcus faecalis.

There is increasing recognition of the emerging role of manganese regulation and acquisition in some pathogenic bacteria. Expression of the Enterococcus faecalis endocarditis-associated virulence factor EfaA is induced by growth in serum. It is demonstrated here that expression of the efaCBA operon encoding a putative ABC-type transporter is regulated by Mn(2+). Transcription of efaCBA and EfaA production were repressed in Mn(2+)-supplemented medium. A Mn(2+)-responsive transcriptional regulator, EfaR, sharing 27 % identity with the Corynebacterium diphtheriae diphtheria toxin repressor (DtxR), was identified. In the presence of Mn(2+), EfaR protein bound in vitro to the efaC promoter region. Analysis of the E. faecalis V583 genome revealed ten additional putative EfaR-binding sites, suggesting that manganese availability could have a broader regulatory role in infection. The results identify a new Mn(2+)-sensing regulator in enterococci that regulates the expression of a virulence factor implicated in enterococcal endocarditis.

[Genetic effects on grain shape traits of indica black pericarp rice and their genetic correlations with main mineral element contents in grains].

Complete diallel crosses with 7 varieties of indica black pericarp rice were conducted to analyze the genetic effects on grain shape traits such as 100-grain weight, grain length, grain width and length/width and their genetic correlations with main mineral elements of Fe, Zn, Mn and P contents in kernels of parents and their F1s and F2s, by using the full genetic model including seed, cytoplasmic and maternal effects on quantitative traits of seeds in cereal crops. The results indicated that the grain shape traits were controlled by seed direct genetic effects, maternal genetic effects as well as by cytoplasmic effects. The seed direct genetic effects were more important than the maternal genetic effects for grain shape traits, and seed direct additive effects constituted a major part of their genetic effects. The narrow heritabilities of seed direct effects were high for 100-grain weight, grain width and grain length/grain width, while those of seed and maternal effects were intermediate for grain length. Therefore, more attention should be paid to the single seed selection on the 100-grain weight, grain width and grain length/grain width in early generations of hybrid offspring, while in the case of grain length, attention should be paid to single plant selection and single seed selection in late generations. The results also showed that there existed significant genetic correlations of seed direct additive, seed direct dominance, cytoplasm, maternal additive and maternal dominance between most of grain shape traits such as 100-grain weight, grain length, grain width, grain length/grain width and main mineral elements of Fe, Zn, Mn and P contents in grains. The improvement for nutrient quality traits of main mineral elements Fe, Zn, Mn and P contents in indica black pericarp rice could be realized by the indirect selection of grain shape traits in speciality rice quality breeding.

Overexpression of manganese superoxide dismutase gene suppresses spontaneous apoptosis without a resultant alteration in in vivo growth of the mouse fibrosarcoma, FSa-II.

The relationship between spontaneous apoptosis and overexpression of manganese superoxide dismutase (MnSOD) gene was examined in vivo. The mouse fibrosarcoma cells expressing high MnSOD activities due to transfection with the human MnSOD cDNA (SOD-H), or the fibrosarcoma cells transfected with the selectable marker alone (NEO), were transplanted into immune-deficient Fox Chase SCID C.B-17/Icr-scid Jcl mice. Apoptosis in tumors was visually quantified by the in situ end-labeling method. The number of apoptotic cells in the SOD-H tumors was significantly less than that in the NEO tumors. The tumor growth time of the SOD-H tumors to grow from 34 to 500 mm3 in one-half of the mice was slightly longer than that of the NEO tumors, but the difference was not statistically significant. These results suggest that overexpression of MnSOD gene is involved in the suppression of spontaneous apoptosis, without a resultant alteration in the tumor growth.

Ribonuclease P catalysis requires Mg2+ coordinated to the pro-RP oxygen of the scissile bond.

Ribonuclease P (RNase P) is an essential enzyme whose action produces the mature 5' termini of all cellular and organellar transfer RNA molecules. In bacteria, the catalytic subunit of RNase P is an RNA molecule which by itself can bind substrate pre-tRNA, select and hydrolyze the correct phosphodiester bond, and release product tRNA. The simple requirements of the reaction-a monovalent cation such as K+ or NH4+ and the divalent cation Mg2+ (or Mn2+)-have prompted proposals that all aspects of phosphodiester bond hydrolysis might be accomplished by one or more divalent metal cations coordinated to the enzyme or substrate. To precisely localize the ligands of catalytically-involved Mg2+, we assayed cleavage by Escherichia coli RNase P RNA of pre-tRNA in which specific pro-Rp phosphate oxygens were replaced with sulfur. RNase P cleavage was targeted to that bond, at or nearest to the normal cleavage site, at which Mg2+ or Mn2+ could be coordinated. Single-turnover kinetics demonstrated that the apparent rate constant for the hydrolysis event was determined quantitatively by the affinity of the divalent cation (Mg2+ or Mn2+) for the atom (O or S) at the pro-Rp position of the scissile phosphodiester bond. We propose a model for pre-tRNA cleavage in which an essential Mg2+ ion is coordinated directly to the pro-Rp phosphate oxygen and indirectly to two other ligands near the scissile bond: the upstream ribose 2'-hydroxyl and the downstream purine N7. This catalytic Mg2+ ion most likely positions and deprotonates a water molecule for in-line nucleophilic attack on the scissile bond phosphorus.

Manganese protects against heart mitochondrial lipid peroxidation in rats fed high levels of polyunsaturated fatty acids.

We demonstrated previously that dietary manganese (Mn) deficiency depressed Mn concentrations in most tissues and consistently depressed Mn superoxide dismutase (MnSOD) levels in heart. To examine the functional consequences of these effects, we fed weanling male Sprague-Dawley rats (n = 12/diet) diets containing 20% (wt/wt) corn oil or 19% menhaden oil + 1% corn oil by weight and 0.75 or 82 mg Mn/kg diet for 2 mo (the fish oil mixture was supplemented with (+)-(mixed)-alpha-tocopherol to the level in corn oil). Heart and liver Mn concentrations in the Mn-deficient rats were 56% of those in Mn-adequate rats (P < 0.0001), confirming Mn deficiency. The Mn-deficient rats had more conjugated dienes in heart mitochondria than Mn-adequate rats (P < 0.001); rats fed fish oil had more conjugated dienes than those fed corn oil (P < 0.001). The MnSOD activity was inversely correlated with conjugated dienes (r = -0.71, P < 0.005), and Mn-deficient rats had 37% less MnSOD activity in the heart than did Mn-adequate rats (P < 0.0001). The dietary treatments did not affect heart microsomal conjugated diene formation, possibly because of compensation by copper-zinc (CuZn) SOD activity; CuZnSOD activities were 35% greater in the hearts of Mn-deficient animals (P < 0.01). Liver was less sensitive to Mn deficiency than was the heart as judged by MnSOD activity and conjugated diene formation. This work is the first to demonstrate that dietary Mn protects against in vivo oxidation of heart mitochondrial membranes.

Trace elements in nutrition for premature infants.

Ten trace elements that are nutritionally essential include: zinc, copper, selenium, chromium, manganese, molybdenum, cobalt, fluoride, iodine, and iron. This article briefly reviews the biochemistry of these trace elements, describes clinical deficiency states, and provides a rationale for recommended enteral and parenteral intakes for preterm infants.

An RNA-dependent RNA polymerase activity associated with virions of tomato spotted wilt virus, a plant- and insect-infecting bunyavirus.

An RNA-dependent RNA polymerase activity was found associated with virions of tomato spotted wilt virus (TSWV), a plant- and insect-infecting member of the family Bunyaviridae. Radiolabeled nucleoside triphosphates were incorporated into trichloroacetic acid-precipitable products by detergent-disrupted, purified TSWV virions. Incorporation was reduced to near-background levels when RNase was present in the reaction mixture. The predominantly double-stranded RNA products were RNase-resistant at high but not low salt concentrations. The activity required manganese and was independent of a DNA template. Discrete products of approximately 3.0 kb and heterogeneous smaller products were synthesized that hybridized to purified TSWV RNA and transcripts of cDNA clones encompassing parts of each of the three genomic RNAs. The predominant products were viral sense although significant amounts of viral complementary sense S RNA products were also synthesized.

Ureidoglycolate amidohydrolase from developing French bean fruits (Phaseolus vulgaris [L.].).

Ureidoglycolate is an intermediate of allantoin catabolism in ureide-transporting legumes. This report describes the first purification of ureidoglycolate degrading activity (UGDA) from plant tissue in which the enzyme has been separated from urease. The enzyme from developing fruits of Phaseolus vulgaris has been purified 48-fold to give a preparation free of allantoinase and urease activity. UGDA was inhibited by EDTA while the Vmax was increased in the presence of Mn2+. The Km values for ureidoglycolate in the presence and the absence of Mn2+ were 2.0 and 5.4 mM, respectively. In the absence of Mn2+ UGDA was heat labile at 40 degrees C, but in the presence of Mn2+ the activity was stable up to temperatures of 60 degrees C. The Mr of UGDA was determined to be 300,000 by gel filtration chromatography and the pH optimum ranged from pH 7.0 to 8.5. Ammonia was determined to be the nitrogen-containing product of UGDA by a microdiffusion assay. This enzyme should therefore be described as ureidoglycolate amidohydrolase. The activity was shown to be associated with peroxisomes by fractionation of a crude extract on a sucrose density gradient. The products of ureidoglycolate degradation are glyoxylate, ammonia, and presumably carbon dioxide, which can be readily utilized by pathways of metabolism that are known to be present in this organelle.

Physiology and metabolism of essential trace elements: an outline.

Man depends on at least nine trace elements--iron, zinc, copper, manganese, iodine, chromium, selenium, molybdenum and cobalt--for optimum metabolic function. These elements serve a variety of functions including catalytic, structural and regulatory activities in which they interact with macromolecules such as enzymes, pro-hormones, pre-secretory granules and biological membranes. These micronutrients are involved, therefore, in all major metabolic pathways at levels which are so fundamental that the features of deficiency of many of them are protean and non-specific. In considering the metabolism of the elements themselves, they fall into two groups: those which exist normally as cations and those present as anions. The latter group are absorbed relatively easily and whole-body homeostasis is mediated mainly by renal excretion. The cations need specific pathways for absorption and their homeostasis is effected by gastrointestinal and biliary secretion. Some elements are absorbed more efficiently as organic complexes. The net achievement of the metabolic pathways for each element is to deliver it to its functional site(s) by exploiting its physicochemical characteristics to avoid interactions with other inorganic nutrients.

Risks and benefits of nutritional supplements during pregnancy.

This review emphasizes the role of minerals and vitamins in pregnancy. Of the trace elements, iron, copper, zinc, and iodine have a fundamental role in human nutrition. Supplementation of iron, zinc, and iodine in the diet of all pregnant women, when dietary deficiencies exist, seems justified. The average diet in developed countries contains sufficient amounts of various vitamins, with the exception of folic acid, which may require supplementation. However, in developing nations and among poor populations in which the diet is inadequate, additional supplies of micronutrients are advisable.

Rationale for adding trace elements to total parenteral nutrient solutions--a brief review.

The physiologic importance of trace element supplementation to total parenteral nutrition solutions is discussed. The trace elements discussed are copper, zinc, manganese and iodide.