Effect of long-term swimming exercise on zinc,magnesium, and copper distribution in aged rats

Trace element content of different tissues might be altered by both age and exercise training. We aimed to determine the effects of a 1-yr swimming protocol (60 min/d, 5 day/wk) on tissue levels and the distribution of zinc (Zn), magnesium (Mg), and copper (Cu) in aging rats. Three groups were formed: sedentary and trained old groups and a young control group. Tissue Zn, Mg, and Cu concentrations were measured in the kidney, heart, liver, lungs, and gastrocnemius and soleus muscles. Kidney zinc concentration significantly decreased in the sedentary old group compared to the young control group (p<0.01) and was significantly higher in the trained old group compared to the sedentary old group (p<0.01), whereas Zn levels in the soleus muscle significantly increased in the sedentary old group in comparison to young controls (p<0.05). Tissue Mg concentrations remained unchanged. The sedentary old group exhibited a significant decrease in kidney Cu concentration compared to the young control group (p<0.01). Although kidney Cu levels also decreased in trained old rats in comparison to young controls (p<0.05), they were significantly higher than in sedentary old rats (p<0.01). The decrease in kidney Zn and Cu content as a result of aging was partly prevented by long-term swimming exercise.     

Discovery and characterization of electron transfer proteins in the photosynthetic bacteria

Research on photosynthetic electron transfer closely parallels that of other electron transfer pathways and in many cases they overlap. Thus, the first bacterial cytochrome to be characterized, called cytochrome c ₂, is commonly found in non-sulfur purple photosynthetic bacteria and is a close homolog of mitochondrial cytochrome c. The cytochrome bc ₁ complex is an integral part of photosynthetic electron transfer yet, like cytochrome c ₂, was first recognized as a respiratory component. Cytochromes c ₂ mediate electron transfer between the cytochrome bc ₁ complex and photosynthetic reaction centers and cytochrome a-type oxidases. Not all photosynthetic bacteria contain cytochrome c ₂; instead it is thought that HiPIP, auracyanin, Halorhodospira cytochrome c551, Chlorobium cytochrome c555, and cytochrome c ₈ may function in a similar manner as photosynthetic electron carriers between the cytochrome bc ₁ complex and reaction centers. More often than not, the soluble or periplasmic mediators do not interact directly with the reaction center bacteriochlorophyll, but require the presence of membrane-bound intermediates: a tetraheme cytochrome c in purple bacteria and a monoheme cytochrome c in green bacteria. Cyclic electron transfer in photosynthesis requires that the redox potential of the system be delicately poised for optimum efficiency. In fact, lack of redox poise may be one of the defects in the aerobic phototrophic bacteria. Thus, large concentrations of cytochromes c ₂ and c′ may additionally poise the redox potential of the cyclic photosystem of purple bacteria. Other cytochromes, such as flavocytochrome c (FCSD or SoxEF) and cytochrome c551 (SoxA), may feed electrons from sulfide, sulfur, and thiosulfate into the photosynthetic pathways via the same soluble carriers as are part of the cyclic system. This revised version was published online in August 2006 with corrections to the Cover Date.     

Identification of a copper transporter family in Arabidopsis thaliana

Despite copper ions being crucial in proteins participating in plant processes such as electron transport, free-radical elimination and hormone perception and signaling, very little is known about copper inward transport across plant membranes. In this work, a five-member family (COPT1–5) of putative Arabidopsis copper transporters is described. We ascertain the ability of these proteins to functionally complement and transport copper in the corresponding Saccharomyces cerevisiae high-affinity copper transport mutant. The specific expression pattern of the Arabidopsis COPT1–5 mRNA in different tissues was analyzed by RT-PCR. Although all members are ubiquitously expressed, differences in their relative abundance in roots, leaves, stem and flowers have been observed. Moreover, steady-state COPT1 and COPT2 mRNA levels, the members that are most efficacious in complementing the S. cerevisiae high-affinity copper transport mutant, are down-regulated under copper excess, consistent with a role for these proteins in copper transport in Arabidopsis cells.     

A core mutation affecting the folding properties of a soluble domain of the ATPase protein CopA from Bacillus subtilis

The two N-terminal domains of the P-type copper ATPase, CopAa and CopAb, from Bacillus subtilis differ in their folding capabilities in vitro. Whereas CopAb has the typical betaalphabetabetaalphabeta structure and is a rigid protein, CopAa is found to be largely unfolded. A sequence analysis of the two and of orthologue homologous proteins indicates that Ser46 in CopAa may destabilise the hydrophobic core, as also confirmed through a bioinformatic energy study. CopAb has a Val in the corresponding position. The S46V and S46A mutants are found to be folded, although the latter displays multiple conformations. S46VCopAa, in both apo and copper(I) loaded forms, has very similar structural and dynamic properties with respect to CopAb, besides a different length of strand beta2 and beta4. It is intriguing that the oxygen of Thr16 is found close, though at longer than bonding distance, to copper in both domains, as it also occurs in a human orthologue domain. This study contributes to understanding the behaviour of proteins that do not properly fold in vitro. A possible biological significance of the peculiar folding behaviour of this domain is discussed.     

Saccharomyces cerevisiae wine strains differing in copper resistance exhibit different capability to reduce copper content in wine

Two wine strains of Saccharomyces cerevisiae, characterized by a different degree of copper resistance, were tested in grape must fermentation in the presence of different copper concentrations. The sensitive strain SN9 was strongly affected by copper concentration (32 ppm, (32 mg/l)), whereas the resistant strain SN41 exhibited a good growth activity in presence of 32 ppm of copper and only a reduced activity in presence of 320 ppm. The different strain fermentation performance in response to the copper addition corresponded to a different capability to accumulate copper inside the cells. Both strains exhibited the capacity to reduce the copper content in the final product, eventhough a significantly greater reducing activity was exerted by the resistant strain SN41, which was able to reduce by 90% the copper concentration in the final product and to accumulate the metal in great concentrations in the cells. As high concentrations of copper can be responsible for wine alterations, the selection of S. cerevisiae strains possessing high copper resistance and the ability to reduce the copper content of wine has a great technological interest, in particular for the fermentation of biological products. From the results obtained, the technique proposed is not only suitable for the assay of copper residues in must, wine and yeast cells, but it also offers the advantage of easy sample preparation and low detection limit in the ppb (g/l) range.     

A kinetic study on the copper-albumin catalyzed oxidation of ascorbate

Serum albumin can specifically bind one Cu(II)-ion, and is proposed to function as a copper transport protein in vivo. Cu(II)-albumin is rapidly reduced by ascorbate. A second order rate constant of 0.54 mM^–1 min^–1 was estimated for the reaction. The oxidation process is catalytic, the Cu(I)-albumin molecule being reoxidized by molecular oxygen. The reaction was found to follow Michaelis-Menten kinetics, characterized by an apparent K_m-value of 0.89 mM, and a catalytic constant of 0.066 M O₂/min. An apparent inhibition of oxygen uptake was obtained with catalase (but not with superoxide dismutase), suggesting the formation of H₂O₂ in the system. Wilson's disease patients usually have increased amounts of non-ceruloplasmin copper in plasma. The low level of plasma ascorbate observed in such patients could possibly be due, at least in part, to an oxidation by Cu(II)-albumin.     

A pH dependence study on the unfolding and refolding of apoazurin

Azurin, a small blue copper protein from the bacterial species Pseudomonas aeruginosa, is mostly a β-sheet protein arranged into a single domain. Previous folding studies have shown that the equilibrium denaturation of the holoprotein follows a two-state process; however, upon removal of the copper, the denaturation had been reported to follow a three-state process. The two unfolding transitions measured for apoazurin had been thought to arise from two different folding domains. However, in the present work, we found that the denaturation of apoazurin occurs over a single transition and we determined the folding free energy to be −27.8±2.4 kJ mol⁻¹. From this measurement along with measurements previously reported for the unfolding of the holoazurin, we were able to determine that Cu(II) and Cu(I) stabilize the native structure by 25.1±6.9 kJ/mol and 12.9±8.1 kJ/mol, respectively. It is our contention that the second transition displayed in the denaturation curves previously reported for apoazurin arise from protein heterogeneity—in particular, from the presence of Zn(II) azurin. We extended our investigation into the denaturation of Zn(II) azurin at pH 6.0 and 7.5. The equilibrium denaturation studies show that the zinc ion significantly stabilizes the native-state structure at pH 7.5 and very little at the lower pH. We attribute the decrease in the stabilizing effect of the zinc ion with decreasing pH to the protonation of two histidinyl side chains. When protonated the ligands, His 46 and His 117, are incapable of binding a metal ion. Further, comparing the denaturation curves of Zn(II) azurin measured by circular dichroism with those measured by fluorescence indicates that the denaturation of Zn(II) azurin is far less simple than the denaturation of apoazurin.     

X-ray structural studies of the fungal laccase from Cerrena maxima

Laccases are members of the blue multi-copper oxidase family. These enzymes oxidize substrate molecules by accepting electrons at a mononuclear copper centre and transferring them to a trinuclear centre. Dioxygen binds to the trinuclear centre and following the transfer of four electrons is reduced to two molecules of water. The X-ray structure of a laccase from Cerrena maxima has been elucidated at 1.9 A resolution using synchrotron data and the molecular replacement technique. The final refinement coefficients are Rcryst = 16.8% and Rfree = 23.0%, with root mean square deviations on bond lengths and bond angles of 0.015 A and 1.51 degrees , respectively. The type 1 copper centre has an isoleucine residue at the axial position and the "resting" state of the trinuclear centre comprises a single oxygen (OH) moiety asymmetrically disposed between the two type 3 copper ions and a water molecule attached to the type 2 ion. Several carbohydrate binding sites have been identified and the glycan chains appear to promote the formation of well-ordered crystals. Two tyrosine residues near the protein surface have been found in a nitrated state.     

Effect of supplemental magnesium on the kidney levels of cadmium, zinc, and copper of mice exposed to toxic levels of cadmium

In this report, we present the results of our investigations on the effect of Mg pretreatment on Cd and bioelements (Cu and Zn) contents in kidney of mice exposed to acute and subacute Cd intoxication. Acute intoxication was performed on male Swiss mice given a single oral dose of 20 mg Cd/kg body weight and mice given the same dose of Cd but pretreated with 40 mg Mg/kg body weight. For subacute intoxication one group of mice was given 10 mg Cd/kg body weight every day, for 2 wk, and the other one received the same dose of Cd after oral Mg intake of 20 mg/kg body weight. Cd, Cu, and Zn content was determined in kidney by atomic absorption spectrophotometry. In acute Cd intoxication, Mg pretreatment resulted in significant decrease of Cd in kidney after 4 and 6 h, compared with animals given only Cd. Under the condition of subacute Cd intoxication, Mg supplementation reduced Cd kidney content after 2 wk for about 30%, compared with animals treated with Cd only. The effect of Mg on Cu and Zn kidney content was also beneficial.     

Teniasis

The aim of this study was to investigate the changes of level of the essential elements of copper, magnesium, and zinc status in cases of teniasis in children. Copper, magnesium, and zinc levels were measured in 40 children who were positive for intestinal parasite of Taenia saginata. Scores were obtained for the positives and their 30 age- and sex-matched T. saginata-negative healthy children. The mean concentration of copper, magnesium, and zinc in blood showed no statistically difference in T. saginata-positive children than in their controls both in females (p>0.05) and males (p>0.05). However, a clear numerically decrease was observed especially in magnesium and zinc levels compared to the controls both in females and males. The average magnesium concentration in T. saginata-positive female children and male children were 20±1.9 and 22±2.2 mg/L and it was 27±2.1 and 27±2.3 mg/L in controls, respectively. The mean values of the zinc in blood were 0.76±0.5 and 0.72±0.4 mg/L in T. saginata-positive female children and male children and 0.85±0.3 and 0.81±0.5 mg/L in female and male controls, respectively. No correlation could be demonstrated between age and mean values of copper, magnesium, and zinc in T. saginata-positive females and males and controls (p>0.05). No significant correlation could be found between blood copper, magnesium and zinc levels in T. saginata-positive female and male children and controls (p>0.05). Although there was no statistical correlation observed in copper, magnesium, and zinc levels between patients and controls, there seem to be, especially in magnesium and zinc levels, a decrease, whereas no change was seen in the zinc level in children infected with T. saginata compared to controls.