Metal chelates of 2-hydroxy-4-methylthiobutanoic acid in animal feeding: preliminary investigations on stability and bioavailability

The alpha-hydroxyacid 2-hydroxy-4-methylthiobutanoic acid (the so-called methionine hydroxy-analogue, MHA), largely used in animal nutrition as a source of methionine, forms stable metal chelates with divalent metals of formula [[CH(3)SCH(2)CH(2)CH(OH)COO](2)M].ZnH(2)O. Protonation and zinc(II) complex formation constants have been determined by pH-metry at 25 degrees C; the ternary system Zn(2+)/MHA/glycine was also studied by pH-metry and the formation constant of the species [ZnLA] was determined [log beta=6.57(11)]. Experiments in vitro with human intestinal CACO-2 cells indicated that the MHA/Fe chelate was taken up by the cells without any apparent toxic effect.     

Fate of Labeled Hydroxamates During Iron Transport from Hydroxamate-Iron Chelates

The fate of the hydroxamic acid-iron transport cofactors during iron uptake from the (59)Fe(3+) chelates of the (3)H-labeled hydroxamates schizokinen and aerobactin was studied by assay of simultaneous incorporation of both (59)Fe(3+) and (3)H. In the schizokinen-producing organism Bacillus megaterium ATCC 19213 transport of (59)Fe(3+) from the (3)H-schizokinen-(59)Fe(3+) chelate at 37 C was accompanied by rapid uptake and release (within 2 min) of (3)H-schizokinen, although (3)H-schizokinen discharge was temperature-dependent and did not occur at 0 C. In the schizokinen-requiring strain B. megaterium SK11 similar release of (3)H-schizokinen occurred only at elevated concentrations of the double-labeled chelate; at lower chelate concentrations, (3)H-schizokinen remained cell-associated. Temperature-dependent uptake of deferri (iron-free) (3)H-schizokinen to levels equivalent to those incorporated from the chelate form was noted in strain SK11, but strain ATCC 19213 showed only temperature-independent binding of low concentrations of deferri (3)H-schizokinen. These results indicate an initial temperature-independent binding of the ferric hydroxamate which is followed rapidly by temperature-dependent transport of the chelate into the cell and an enzyme catalyzed separation of iron from the chelate. The resulting deferri hydroxamate is discharged from the cell only when a characteristic intracellular concentration of the hydroxamate is exceeded, which happens in the schizokinen-requiring strain only at elevated concentrations of the chelate. This strain also appears to draw the deferri hydroxamate into the cell by a temperature-dependent mechanism. The aerobactin-producing organism Aerobacter aerogenes 62-1 also demonstrated rapid initial uptake and temperature-dependent discharge of (3)H-aerobactin during iron transport from (3)H-aerobactin-(59)Fe(3+), suggesting a similar ferric hydroxamate transport system in this organism.     

The characterisation of structural and antioxidant properties of isoflavone metal chelates

Isoflavone metal chelates are of interest as isoflavones act as oestrogen mimics. Metal interactions may enhance isoflavones biological properties so understanding isoflavone metal chelation is important for the commercial application of isoflavones. This work aimed to determine if isoflavones, daidzein (4',7-dihydroxyisoflavone) and genistein (4',5,7-trihydroxyisoflavone) could chelate with metals as isoflavone chelates. Biochanin A (4'-methoxy-5,7-dihydroxyisoflavone) was also examined for it's ability to chelate with Cu(II) and Fe(III). This study found daidzein does not chelate with Cu(II) and Fe(III) but genistein and biochanin A chelate with a 1:2 M/L stoichiometry. The copper and iron chelates were synthesised and characterised by elemental analysis, FTIR, thermogravimetric analysis (TGA) and electrospray ionisation mass spectrometry (ESI-MS). These studies indicated a 1:2 M/L stoichiometry and suggested the isoflavones bind with the metals at the 4-keto and the 5-OH site. 2,2-diphenyl-1-picrylhydrazyl (DPPH) inhibition assays showed that copper isoflavone chelates have higher antioxidant activity than free isoflavones while the iron isoflavone chelates showed pro-oxidant activity compared to the free isoflavone. Synergistic DPPH studies with 0.02 mM ascorbic acid revealed copper chelates exhibit reduced antioxidant activity versus free isoflavones whereas the iron chelates showed lower pro-oxidant activity except at 1.0 mM.     

Microsomal lipid peroxidation: mechanisms of initiation. The role of iron and iron chelators

The role of iron and iron chelators in the initiation of microsomal lipid peroxidation has been investigated. It is shown that an Fe3+ chelate in order to be able to initiate enzymically induced lipid peroxidation in rat liver microsomes has to fulfill three criteria: (a) reducibility by NADPH; (b) reactivity of the Fe2+ chelate with rat liver microsomes has to fulfill three criteria: (a) reducibility by NADPH; (b) reactivity of the Fe2+ chelate with O2; and (c) formation of a relatively stable perferryl radical. NADH can support lipid peroxidation in the presence of ADP-Fe3+ or oxalate-Fe3+ at rates comparable to those obtained with NADPH but requires 10 to 15 times higher concentrations of the Fe3+ chelates for maximal activity. The results are discussed in relation to earlier proposed mechanisms of microsomal lipid peroxidation.     

Preparation of metal ion buffers for biological experimentation: a methods approach with emphasis on iron and zinc

Transition metal ions are a challenge to study in physiology because of problems associated with solubility, oxidation, binding, and attaining appropriate free activities in solution. This review discusses these problems and potential ways of accommodating them. Special attention is given to iron and zinc ions, but many of the concepts can be applied for studying other transition metals. Selection of reagents appropriate for metal work (including water, salts, noncomplexing pH buffers) is briefly discussed. Calculation of the solubility product (K(sp)) for common iron and zinc precipitates is covered, as well as techniques used to solubilize Fe(3+) with organic chelates. Factors that affect Fe(2+) oxidation are mentioned, and the use of ascorbate as a reducing agent is considered. Measurement of the rate of Fe(2+) oxidation (or Fe(3+) reduction) with the Fe(2+) chromophores ferrozine and BPS is also discussed. Generation of a free metal ion activity through use of metal buffers (chelators) is discussed. Theoretical problems associated with this technique are explored, and selected shareware metal ion buffer calculators are described. Finally, techniques for measuring and minimizing nonspecific binding of iron and zinc ions to biological membranes are considered.     

Structural studies in solution and in the solid state on the zinc chelate of 2-hydroxy-(4-methylthio)butanoic acid, an effective mineral supplement in animal feeding

The bis-chelate complex of Zn²⁺ with 2-hydroxy-(4-methylthio)butanoate (MHA_-H the anion derived from the so-called methionine hydroxy-analogue, MHA) is an effective, bioavailable mineral supplement for animal feeding. It can be obtained in two solid forms: the anhydrous [Zn(OC(O)CH₂CH(OH)CH₂CH₂SCH₃)₂] and the corresponding dihydrate species, both well distinguishable by IR spectroscopy and powder X-ray diffraction. The crystal and molecular structure of the dihydrate form has been solved by single-crystal X-ray diffraction. It consists of dinuclear bis-chelate species with a bridging carboxylate group, both zinc atoms displaying hexacoordination involving all the hydroxyl and carboxyl groups from the four MHA_-H anions and three oxygens from different water molecules. The fourth water molecule does not participate in coordination. Therefore, the dihydrate complex must be formulated as [Zn₂(OC(O)CH₂CH(OH)CH₂CH₂SCH₃)₄(H₂O)₃] · H₂O (1). A molecular computational analysis has been carried out by density functional theory (DFT) on three possible MHA_-H zinc chelates, i.e. the dinuclear bis-chelate observed in the solid state, the mononuclear bis-chelate diaquo-complex, and the monochelate tetraaquo-complex. Calculations have suggested that between the dinuclear and mononuclear bis-chelates, the preferred form in aqueous solution may be the second one. Moreover, both ¹H (chemical shifts and relaxation rates) and ¹³C NMR data provide further evidence for the formation of Zn/MHA_-H chelates in solution.     

Zinc supplementation decreases the development of atherosclerosis in rabbits

Developing atherosclerotic plaques in cholesterol-fed rabbits are enriched in iron but depleted in zinc. In order to examine further the role of zinc, New Zealand White rabbits were fed a high-cholesterol 1% (w/w) diet with zinc (1 g/kg) supplementation for 8 weeks. After the 8-week period, the average atherosclerotic lesion cross-sectional areas in the aortas of the animals fed with the zinc supplement were significantly decreased (1.0 mm2) compared with lesion areas of the animals fed only on the high-cholesterol diet (3.1 mm2). Using nuclear microscopy, a technique for mapping and measuring trace elements in tissue sections, lesion zinc levels (24 ppm) were observed to be unchanged in the zinc-fed rabbits compared to controls. However, average lesion Fe levels in the zinc-fed group were measured at 32 ppm, whereas in the control group the average Fe levels were significantly higher at 43 ppm (P = 0.03). Our data support the concept that zinc may have an antiatherogenic effect by decreasing iron levels in the lesion, possibly leading to inhibition of iron-catalyzed free radical reactions.     

Sequence-selective cleavage of oligoribonucleotides by 3d transition metal complexes of 1,5,9-triazacyclododecane-functionalized 2'-O-methyl oligoribonucleotides

2'-O-Methyl oligoribonucleotides bearing a 3'-[2,6-dioxo-3,7-diaza-10-(1,5,9-triazacyclododec-3-yl)decyl phospate conjugate group have been shown to cleave in slight excess of Zn(2+) ions complementary oligoribonucleotides at the 5'-side of the last base-paired nucleotide. The cleavage obeys first-order kinetics and exhibits turnover. The acceleration compared to the monomeric Zn(2+) 1,5,9-triazacyclododecane chelate is more than 100-fold. In addition, 2'-O-methyl oligoribonucleotides having the 1,5,9-triazacyclododec-3-yl group tethered to the anomeric carbon of an intrachain 2-deoxy-beta-d-erythro-pentofuranosyl group via a 2-oxo-3-azahexyl, 2,6-dioxo-3,7-diazadecyl, or 2,9-dioxo-3,10-diazatridecyl linker have been studied as cleaving agents. These cleave as zinc chelates a tri- and pentaadenyl bulge opposite to the conjugate group approximately 50 times as fast as the monomeric chelate and show turnover. The cleavage rate is rather insensitive to the length of linker. Interestingly, a triuridyl bulge remains virtually intact in striking contrast to a triadenyl bulge. Evidently binding of the zinc chelate to a uracil base prevents its catalytic action. Replacement of Zn(2+) with Cu(2+) or Ni(2+) retards the cleaving activity of all the cleaving agents tested.     

The lipophilic iron compound TMH-ferrocene [(3,5,5-trimethylhexanoyl)ferrocene] increases iron concentrations,neuronal L-ferritin,and heme oxygenase in brains of BALB/c mice

Mismanagement of intracellular iron is a key pathological feature of many neurodegenerative diseases. Our long-term goal is to use animal models to investigate the mechanisms of iron neurotoxicity and its relationship to neurodegenerative pathologies. The immediate aim of this experiment was to determine regional distribution of iron and cellular distribution of iron storage proteins (l- and h-ferritin) and an oxidative stress marker (heme oxygenase-1) in brains of mice fed the lipophilic iron compound (3,5,5-trimethylhexanoyl) (TMH)-ferrocene. We fed male and female weanling BALB/cj mice diets either deficient in iron (0 mg Fe/kg diet), adequate in iron (35 mg Fe/kg diet; control mice), or adequate in iron and supplemented with 0.1 or 1.0 g TMH-ferrocene/kg diet for 8 wk. Iron concentrations in cerebrum were higher in mice fed 1.0 g TMH-ferrocene/kg diet than in control mice (p<0.05). Liver iron concentrations were eightfold higher in mice fed 1.0 g TMH-ferrocene/kg diet than in control mice (p<0.0001). l-Ferritin and heme oxygenase-1 expression were elevated in striatum in mice fed 1.0 g TMH-ferrocene/kg diet. We conculde that administration of the lipophilic iron compound TMH-ferrocene leads to subtle perturbations of cellular iron within the brain, potentially representing a model of iron accumulation similar to that seen in various neuropathological conditions.     

Effect of dietary nickel and iron on the trace element content of rat liver

The level and/or form of dietary iron, dietary nickel, and the interaction between them affected the trace element content of rat liver. Livers were from the offspring of dams fed diets containing 10–16 ng, or 20 μg, of nickel/g. Dietary iron was supplied as ferric chloride (30 μg/g) or ferric sulfate (30 μg, or 60 μg). In nickel-deprived rats fed 60 μg of iron/g of diet as ferric sulfate, at age 35 days, levels of iron and zinc were depressed in liver and the level of copper was elevated. At age 55 days, iron was still depressed, copper was still elevated, but zinc also was elevated. In rats fed 30 μg of iron/g of diet as ferric chloride, liver iron content was higher in nickel-deprived than in nickel-supplemented rats at 30, but not at 50, days of age. Also manganese and zinc were lower in nickel-deprived than in nickel-supplemented rats at age 35 days if their dams had been on experiment for an extended period of time (i.e., since age 21 days). Thus, the levels of copper, iron, manganese, and zinc in liver were affected by nickel deprivation, but the direction and extent of the affects depended upon the iron status of the rat.     

Iron transporters in marine prokaryotic genomes and metagenomes

In the pelagic environment, iron is a scarce but essential micronutrient. The iron acquisition capabilities of selected marine bacteria have been investigated, but the recent proliferation of marine prokaryotic genomes and metagenomes offers a more comprehensive picture of microbial iron uptake pathways in the ocean. Searching these data sets, we were able to identify uptake mechanisms for Fe(3+), Fe(2+) and iron chelates (e.g. siderophore and haem iron complexes). Transport of iron chelates is accomplished by TonB-dependent transporters (TBDTs). After clustering the TBDTs from marine prokaryotic genomes, we identified TBDT clusters for the transport of hydroxamate and catecholate siderophore iron complexes and haem using gene neighbourhood analysis and co-clustering of TBDTs of known function. The genomes also contained two classes of siderophore biosynthesis genes: NRPS (non-ribosomal peptide synthase) genes and NIS (NRPS Independent Siderophore) genes. The most common iron transporters, in both the genomes and metagenomes, were Fe(3+) ABC transporters. Iron uptake-related TBDTs and siderophore biosynthesis genes were less common in pelagic marine metagenomes relative to the genomic data set, in part because Pelagibacter ubique and Prochlorococcus species, which almost entirely lacked these Fe uptake systems, dominate the metagenomes. Our results are largely consistent with current knowledge of iron speciation in the ocean, but suggest that in certain niches the ability to acquire siderophores and/or haem iron chelates is beneficial.     

Effects of Acute Dietary Iron Overload in Pigs (Sus scrofa) with Induced Type 2 Diabetes Mellitus

Epidemiological studies have reported an association between high iron (Fe) levels and elevated risk of developing type 2 diabetes mellitus (T2D). It is believed that the formation of Fe-catalyzed hydroxyl radicals may contribute to the development of diabetes. Our goal was to determine the effect of a diet with a high Fe content on type 2 diabetic pigs. Four groups of piglets were studied: (1) control group, basal diet; (2) Fe group, basal diet with 3,000 ppm ferrous sulfate; (3) diabetic group (streptozotocin-induced type 2 diabetes) with basal diet; (4) diabetic/Fe group, diabetic animals/3,000 ppm ferrous sulfate. For 2 months, biochemical and hematological parameters were evaluated. Tissue samples of liver and duodenum were obtained to determine mRNA relative abundance of DMT1, ferroportin (Fpn), ferritin (Fn), hepcidin (Hpc), and transferrin receptor by qRT-PCR. Fe group presented increased levels of hematological (erythrocytes, hematocrit, and hemoglobin) and iron parameters. Diabetic/Fe group showed similar behavior as Fe group but in lesser extent. The relative abundance of different genes in the four study groups yielded a different expression pattern. DMT1 showed a lower expression in the two iron groups compared with control and diabetic animals, and Hpc showed an increased on its expression in Fe and diabetic/Fe groups. Diabetic/Fe group presents greater expression of Fn and Fpn. These results suggest that there is an interaction between Fe nutrition, inflammation, and oxidative stress in the diabetes development.     

Microsomal reduction of low-molecular-weight Fe3+ chelates and ferritin: enhancement by adriamycin, paraquat, menadione, and anthraquinone 2-sulfonate and inhibition by oxygen

Reduction of iron is important in promoting xenobiotic-enhanced, microsomal lipid peroxidation, yet there is little evidence that Fe3+ chelates that promote lipid peroxidation can be reduced by the microsomal system. We have shown that rat liver microsomes catalyse NADPH-dependent reduction of Fe3+ without chelator, as well as Fe3+(ADP), Fe3+(ATP), Fe3+(citrate), Fe3+(EDTA), and ferrioxamine in N2. The NADPH oxidation that accompanied Fe3+ reduction was inhibited by CO for all chelates, except Fe3+ (EDTA). This implies that, except for Fe3+ (EDTA), cytochrome P450 was involved in reduction of the complexes. Adriamycin, paraquat, and anthraquinone 2-sulfonate (AQS) enhanced reduction of all the Fe3+ chelates, whereas menadione enhanced reduction only of Fe3+(ADP) and Fe3+(citrate). All the compounds enhanced oxidation of NADPH in the presence or absence of iron. This was not inhibited by CO, and the results are compatible with Fe3+ reduction occurring via the xenobiotic radicals produced by cytochrome P450 reductase. Microsomal reduction of the xenobiotics, except menadione, enabled the reduction and release of iron from ferritin. Fe3+ chelate reduction, both with and without xenobiotic, was inhibited by O2, although it still proceeded in air at 10-20% of the rate in N2. Iron-dependent lipid peroxidation was promoted by ADP and ATP, inhibited 50% by citrate, and completely inhibited by EDTA and desferrioxamine. Of the xenobiotics, only Adriamycin enhanced microsomal lipid peroxidation. These results indicate that the effects of chelators and xenobiotics on Fe3+ reduction do not correlate with lipid peroxidation and, although reduction is necessary, there must be other factors involved.     

A comparative study of the ability of ferric nitrilotriacetate [correction of nitriloacetate] and other iron chelators to assist membrane lipid peroxidation by superoxide radicals

This study examined some of the variables determining the efficiency of lipid peroxidation in egg yolk phosphatidylcholine liposomes and in microsomes exposed to enzymatically-generated superoxide radicals. The initiation of peroxidation required the presence of preformed lipid peroxides and a chelated metal catalyst. Comparison of the relative effectiveness of four iron chelating agents showed that the chelate must bind to the membrane by coulombic attraction between the charged membrane and a chelate carrying an opposite net charge. Of the chelates tested, only the carcinogenic ferric nitrilotriacetate [corrected] (Fe(3+)-NTA) was an effective catalyst of oxidation of all membranes, whether carrying a net charge, or not. We postulate that the unique catalytic capacity of the ferric nitrilotriacetate [corrected] (Fe(3+)-NTA) can be explained by its existence in two forms at neutral pH, each binding to oppositely charged membranes and initiating their peroxidation. This gives the complex the unique ability to bind to any membrane, which may be a factor in its carcinogenicity.     

Novel cytotoxic chelators that bind iron(II) selectively over zinc(II) under aqueous aerobic conditions

To achieve cellular iron deprivation by chelation, it is important to develop chelators with selective metal-binding properties. Selectivity for iron has long been the province of certain oxygen-donor chelators such as desferrioxamine, which target Fe(III) and exploit the strength of a relatively ionic Fe(III)-O interaction. We have been studying novel chelators that possess mechanisms to selectively chelate +2 biometals, particularly tachpyr [N,N',N"-tris(2-pyridylmethyl)-1,3,5-cis,cis-triaminocyclohexane] and derivatives from N,N',N"-trialkylation and pyridine ring alkylation. Metal-exchange and metal-binding competition reactions have been conducted at pH 7.4, 37 degrees C and time periods until no further change was observed (generally 24-48 h). Under anaerobic conditions, tachpyr is strongly selective for iron, binding 95+/-5% Fe(II) versus 5+/-5% Zn(II) in the forms [Fe(tachpyr)](2+) and [Zn(tachpyr)](2+) respectively. Under aerobic conditions, tachpyr complexes Fe(II) more effectively than Fe(III), forming iminopyridyl complexes [Fe(tachpyr-ox-n)](2+) (n=2, 4) by O(2)-induced and iron-mediated oxidative dehydrogenation. Complexes [Fe(tachpyr-ox-n)](2+) are also strongly bound forms of iron that are unaffected by an excess of Zn(II) (75 mol zinc:1 mol iron complex). The preference of tachpyr for iron over zinc under aerobic conditions appears to be hindered by oxidation of Fe(II) to Fe(III), such that the proportions bound are 44+/-10% Fe(II) versus 56+/-10% Zn(II), in the respective forms [Fe(tachpyr-ox-n)](2+) and [Zn(tachpyr)](2+). However, upon addition of the reducing agent Na(2)S(2)O(4) that converts Fe(III) to Fe(II), the binding proportions shift to 76+/-10% Fe(II) versus 24+/-10% Zn(II), demonstrating a clear preference of tachpyr for Fe(II) over Zn(II). Iron(II) is in the low-spin state in [Fe(tachpyr)](2+) and [Fe(tachpyr-ox-n)](2+) (n=2, 4), which is a likely cause of the observed selectivity. N-methylation of tachpyr [giving (N-methyl)(3)tachpyr] results in the loss of selectivity for Fe(II), which is attributed to the steric effect of the methyl groups and a resulting high-spin state of Fe(II) in [Fe(N-methyl)(3)tachpyr)](2+). The relationship of chelator selectivity to cytotoxicity in the tach family will be discussed.     

Effects of time and dietary iron on tissue iron concentration as an estimate of relative bioavailability of supplemental iron sources for ruminants

Two experiments were conducted to investigate the effects of time and dietary Fe on tissue Fe concentrations following short-term, high level supplementation for use as a bioassay procedure for supplemental Fe sources for ruminants. In Experiment 1, 28 wethers were allotted randomly to four experimental diets which were fed for 15 or 30 days. The basal maize–soyabean meal–cottonseed hulls diet (193 mg kg⁻¹ Fe) was supplemented with 0, 400, 800 or1200 mg kg⁻¹ added Fe from reagent grade ferrous sulfate (FeSO₄·7H₂O). Iron concentrations in liver, kidney, and spleen increased (P<0.05) as dietary Fe increased; however, muscle, heart, and bone Fe concentrations were unaffected. A logarithmic transformation of liver or kidney Fe concentrations at 30 days regressed on added dietary Fe produced the best fits to a linear model. In Experiment 2, bioavailability of Fe from three feed grade ferrous carbonates known to differ (carbonates A, B, and C) was compared to that from reagent grade ferrous sulfate. The dietary treatments fed for 30 days included the above basal diet (90 mg kg⁻¹ Fe) supplemented with 0, 300, 600 or 900 mg kg⁻¹ added Fe from ferrous sulfate or 600 mg kg⁻¹ Fe from ferrous carbonates A, B, or C. Liver Fe concentrations from sheep fed ferrous sulfate were numerically greater than those of animals fed the carbonate sources or control diet. Kidney Fe concentrations from lambs fed ferrous sulfate at 600 mg kg⁻¹ Fe or carbonate-A were greater (P<0.05) than those fed carbonates B or C. Iron concentrations in spleen were lower (P<0.05) in lambs fed carbonate-B than for those fed 600 mg kg⁻¹ Fe as ferrous sulfate, but were similar to other carbonates. Overall average bioavailability estimates based on multiple regression slope ratios for the three tissues were ferrous sulfate 1.00, carbonate-A 0.55, carbonate-B 0.00, and carbonate-C 0.20. Estimates for carbonates A and C were similar to those based on hemoglobin concentrations reported previously for young swine supplemented at dietary concentrations near the requirement.     

不同形式蛋氨酸对建鲤生长性能及血清游离氨基酸含量的影响

为考察不同形式蛋氨酸对建鲤生长的作用效果, 实验以豆粕、鱼粉、棉粕为蛋白源, 配制缺乏蛋氨酸的基础饲料(对照组, 蛋氨酸含量为0.48%), 在基础饲料中分别添加晶体蛋氨酸、微囊蛋氨酸、蛋氨酸羟基类似物(MHA)及蛋氨酸羟基类似物钙盐(MHA-Ca), 使蛋氨酸含量达到0.58%, 获得5个饲料处理组, 饲养平均体重为(8.61.0) g的建鲤(Cyprinus carpio var Jian)8周。结果显示: 各组鱼体增重率分别为343.51%、350.77%、382.80%、384.02%和385.59%; 饲料系数分别为1.58、1.55、1.42、1.42和1.41; 晶体蛋氨酸组鱼体增重率、饲料系数与对照组无显著差异(P0.05), 微囊蛋氨酸组、MHA组、MHA-Ca组增重率较对照组提高11.4%、11.8%、12.2% (P0.05), 饲料系数降低10.1%、10.1%、10.8% (P0.05)。各处理组在肌肉水分、脂肪含量间无显著差异(P0.05), MHA组肌肉粗蛋白含量较晶体蛋氨酸组显著下降, 其他各组间无显著差异(P0.05)。对摄食后不同时间的血清游离氨基酸浓度变化的分析表明, 对照组在摄食后2h或3h达到峰值, 晶体蛋氨酸组、MHA组在摄食后1h达到吸收峰值, 微囊蛋氨酸组在摄食后1h或2h达到峰值, 而MHA-Ca组则在摄食后3h达到峰值。上述结果表明, 在蛋氨酸缺乏的颗粒饲料中补充晶体蛋氨酸, 对建鲤生长性能无改善作用, 而添加微囊蛋氨酸、蛋氨酸羟基类似物、蛋氨酸羟基类似物钙盐则显著提高了鱼体生长性能, 降低饲料系数。       

Effect of form of iron on nickel deprivation in the rat

In three fully crossed, factorially arranged, completely randomized experiments, female weanling rats were fed a basal diet (containing about 10 ng of nickel and 2.3 μg of iron/g) supplemented with graded levels of nickel and iron. Iron was supplemented to the diet in experiment 1 at levels of 0, 25, 50, and 100 μg/g as a mixture of 40% FeSO₄·nH₂O and 60% Fe₂(SO₄)₃·nH₂O; in experiment 2 at levels of 0, 12.5, 25, 50, and 100 μg/g as Fe₂(SO₄)₃·nH₂O; in experiment 3 at levels of 0, 25, and 50 μg/g as either the mixture of ferric-ferrous sulfates, or as ferric sulfate only. Nickel as NiCl₂·3H₂O was supplemented to the diet in experiment 1 at levels of 0, 5, and 50 μg/g; in experiment 2 at levels of 0 and 50 μg/g; and in experiment 3 at levels of 0 and 5 μg/g. Regardless of dietary nickel, rats fed no supplemental iron exhibited depressed iron content and elevated copper, manganese, and zinc contents in the liver. Nickel and iron did not interact to affect iron, manganese, and zinc in liver. Liver copper was inconsistently affected by an interaction between nickel and iron. Nickel deprivation apparently accentuated the elevation of the copper level in livers of severely iron-deficient rats. Experiment 3 showed that the form of dietary iron altered the effect of nickel deprivation on the iron content of the liver. When only ferric sulfate was supplemented to the diet, liver iron content was depressed in nickel-deprived rats. On the other hand, when the ferric-ferrous mixture was supplemented to the diet, nickel deprivation apparently elevated the iron content in the liver. The findings support the views that (1) parameters that are affected by an interaction between nickel and iron are limited in factorially arranged experiments, and (2) the form and level of dietary iron markedly influence the effect of nickel deprivation in the rat.     

Reactions of peroxyl radicals with Fe(H(2)O)(6)(2+)

The reactions of RO(2)* radicals with Fe(H(2)O)(6)(2+) were studied, R[double bond]H; CH(3); CH(2)COOH; CH(2)CN; CH(2)C(CH(3))(2)OH; CH(2)OH; CHCl(2)/CCl(3). All these processes involve the following reactions: Fe(H(2)O)(6)(2+)+RO(2)*<==>(H(2)O)(5)Fe(III)[bond]OOR(2+) K(1) approximately 250 M(-1); (H(2)O)(5)Fe(III)[bond]OOR(2+)+H(3)O(+)/H(2)O-->Fe(H(2)O)(6)(3+)+ROOH+H(2)O/OH(-); (H(2)O)(5)Fe(III)[bond]OOR(2+)+2Fe(H(2)O)(6)(2+)-->3Fe(H(2)O)(6)(3+)+ROH; 2 RO(2)*-->Products; RO(2)*+(H(2)O)(5)Fe(III)[bond]OOR(2+)-->Fe(H(2)O)(6)(2+)+products. The values of k(1) and k(3) [reaction is clearly not an elementary reaction] approach the ligand exchange rate of Fe(H(2)O)(6)(2+), i.e. these reactions follow an inner sphere mechanism and the rate determining step is the ligand exchange step. The rate of reaction is several orders of magnitude faster than that of the Fenton reaction. Surprisingly enough the K(1) values are nearly independent of the redox potential of the radical and are considerably higher than calculated from the relevant redox potentials. These results indicate that the ROO(-) ligands considerably stabilise the Fe(III) complex, this stabilisation is smaller for radicals with electron withdrawing groups which raise the redox potential of the radical but decrease the basicity of the ROO(-) ligands, two effects which seem to nearly cancel each other. Finally, the results clearly indicate that reaction (5) is relatively fast and affects the nature of the final products. The contribution of these reactions to oxidation processes involving 'Fenton-like' processes is discussed.