Ferric Reducing Activity Research Articles

Riboflavin Biosynthesis Is Associated with Assimilatory Ferric Reduction and Iron Acquisition by Campylobacter jejuni

One of the pathways involved in the acquisition of the essential metal iron by bacteria involves the reduction of insoluble Fe(3+) to soluble Fe(2+), followed by transport of Fe(2+) to the cytoplasm. Flavins have been implicated as electron donors in this poorly understood process. Ferrous iron uptake is essential for intestinal colonization by the important pathogen Campylobacter jejuni and may be of particular importance under low-oxygen conditions. In this study, the links among riboflavin biosynthesis, ferric reduction, and iron acquisition in C. jejuni NCTC11168 have been investigated. A riboflavin auxotroph was generated by inactivation of the ribB riboflavin biosynthesis gene (Cj0572), and the resulting isogenic ribB mutant only grew in the presence of exogenous riboflavin or the riboflavin precursor diacetyl but not in the presence of the downstream products flavin adenine dinucleotide and flavin mononucleotide. Riboflavin uptake was unaffected in the ribB mutant under iron-limited conditions but was lower in both the wild-type strain and the ribB mutant under iron-replete conditions. Mutation of the fur gene, which encodes an iron uptake regulator of C. jejuni, resulted in an increase in riboflavin uptake which was independent of the iron content of the medium, suggesting a role for Fur in the regulation of the as-yet-unknown riboflavin transport system. Finally, ferric reduction activity was independent of iron availability in the growth medium but was lowered in the ribB mutant compared to the wild-type strain and, conversely, increased in the fur mutant. Taken together, the findings confirm close relationships among iron acquisition, riboflavin production, and riboflavin uptake in C. jejuni.

Antioxidative activity of Mungoong, an extract paste, from the cephalothorax of white shrimp ( Litopenaeus vannamei)

The antioxidative activity of Mungoong, an extract paste, from the cephalothorax of white shrimp ( Litopenaeus vannamei) was studied. Extraction media were shown to affect the antioxidative activity and properties of resulting extracts from Mungoong. Distilled water exhibited the highest efficacy in extracting the antioxidants from Mungoong, as evidenced by the highest ABTS (2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) and DPPH (2,2-diphenyl-1-picryl hydrazyl) radical scavenging activity as well as ferric reducing activity power (FRAP), compared with distilled water/ethanol mixture (1:1, 1:2 and 2:1) and ethanol. UV-absorbances at both 280 and 295 nm ( A 280, A 295), browning intensity ( A 420) and fluorescence intensity were also highest in the extract using distilled water. ABTS and DPPH radical scavenging activity and FRAP of water extract, increased linearly with increasing concentration. Good correlation between ABTS and DPPH radical scavenging activity; DPPH radical scavenging activity and FRAP; ABTS radical scavenging activity and FRAP were observed, suggesting that antioxidants in the extract, possessed the capability of scavenging the radicals together with reducing power. Antioxidants in the water extract from Mungoong showed high stability over the wide pH ranges (2–11) and temperature up to 100 °C, in which the activity of more than 80% remained. MALDI-TOF analysis revealed that water extract contained the peptides having the mass ranges of m/z 400–1000 and 4000–7000.

The relationship between micronuclei in human lymphocytes and selected micronutrients in vegetarians and non-vegetarians

A vegetarian diet results in higher intake of vitamins and micronutrients, which – although providing antioxidant defence – may lead to deficiency in other micronutrients involved in DNA metabolism and stability (such as vitamins belonging to the B group). The principal difference among various vegetarian diets is the extent to which animal products are avoided. We have performed a pilot study to determine the relationship between the micronucleus frequency in lymphocytes and diet, and we compared the levels of Vitamins C and E, β-carotene, B 12, folic acid, homocysteine and total antioxidant capacity in healthy vegetarians and non-vegetarians. The vegetarian group, consisting of 24 volunteers (13 women and 11 men), were matched for age and sex with 24 volunteers (12 women and 12 men) with a traditional dietary habit. Among the vegetarians were 13 lacto-ovo-vegetarians with average duration of vegetarian diet 10.8 years (ranging from 5 to 26 years) and 11 lacto-vegetarians with average duration of vegetarian diet 8.2 years (ranging from 3 to 15 years). Homocysteine, Vitamins C and E and β-carotene levels in plasma were assayed by HPLC, and serum folate and Vitamin B 12 were determined with Elecsys Immunoassay tests. The total antioxidant capacity of plasma was estimated by measuring the ferric-reducing activity in a spectrophotometric assay. Micronuclei were measured in cytokinesis-blocked lymphocytes. Vegetarians had significantly higher levels of Vitamin C and β-carotene (but not Vitamin E) in plasma compared with non-vegetarians ( P < 0.001). There were no significant differences in serum levels of folic acid and Vitamin B 12 between the monitored groups. Levels of folic acid in vegetarians correlated with length of vegetarianism ( r = 0.62, P = 0.001, N = 24). Vegetarians had elevated levels of homocysteine compared with non-vegetarians ( P = 0.007), as did vegetarian women compared with non-vegetarian women ( P = 0.031). We did not find any differences in total antioxidant capacity or in micronucleus frequency between the groups. Micronuclei correlated with age ( r = 0.62, P < 0.001, N = 48), women having higher frequencies than men. Multifactorial regression analysis showed significant effects of age, sex and total antioxidant capacity on micronucleus frequency ( N = 48, P < 0.001).

청미래덩굴(Smilax china) 뿌리 추출물의 항산화활성 효과

천연 항산화제 개발 연구의 일환으로 국내에서 민간약재로 사용되고 있는 청미래덩굴 뿌리의 항산화활성을 조사하였다. 건조된 청미래덩굴 뿌리를 물 및 25% 에탄올로 추출하여 얻어진 추출물을 연구시료로 사용하였다. 추출물의 얻어진 양은 건조시료 1.0 g에서 69.3 ㎎, 87.9 ㎎이 각각 얻어졌다. 추출액 1 mL를 동결건조하였을 때 얻어진 양은 23.1 ㎎과 29.0 ㎎이었다. 두 추출물의 총페놀함량은 비교적 높았으며, 건조시료 1.0 g당 약 36 ㎎으로 추출물간 유의적인 차이는 없었다. DPPH 라디칼 형성을 50%로 낮추는데 요구되는 추출물의 농도(SC50)는 물 추출물이 12.1 μL, 에탄올 추출물이 6.3 μL로 에탄올 추출물이 유의적으로 높은 DPPH 소거활성을 보였다. NO 라디칼 소거에 대한 두 추출물의 활성은 50 μL에서 물 추출물이 약 75%, 에탄올 추출물이 88%로 에탄올 추출물이 유의적으로 높은 활성을 보였다(p＜0.05). 두 추출물의 pH를 달리한 조건에서 NO₂ 소거활성을 조사한 결과, pH가 낮을수록 NO₂의 소거활성이 더 높았다. 동일농도 1 mL의 pH 4.2 및 pH 6.0에서는 에탄올 추출물이 유의적으로 높은 활성을 보였다. pH 1.2의 강산 조건에서는 물 추출물과 에탄올 추출물이 유의적인 차이를 보이지는 않았으나, 두 추출물 모두 98% 이상의 높은 NO₂ 라디칼 소거활성을 보였다. Vitamin C의 환원력과 비교했을 때, 0.5 ㎎ 농도에서는 두 추출물의 환원력이 vitamin C보다 낮았으나, 0.1 ㎎ 이하에서는 청미래덩굴 뿌리 추출물이 유의적으로 훨씬 더 높은 환원력을 보였다(p＜0.01). 청미래덩굴 뿌리 추출물의 tyrosinase 활성 저해효과는 추출물 1 mL에서 물 추출물이 44.6%, 에탄올 추출물이 52.6%로 비교적 높은 저해효과를 보였다. 두 추출물의 총 페놀함량이 유의적인 차이를 보이지 않았으나, DPPH 및 NO, NO₂ 라디칼의 소거활성 효과, 환원력, tyrosinase 활성 저해효과는 에탄올 추출물에서 유의적으로 높았으므로 청미래덩굴 뿌리의 경우 페놀화합물 외에도 다른 성분들이 항산화에 관여하는 것으로 판단되었다.

Effect of iron supply and nitrogen form on growth, nutritional status and ferric reducing activity of spinach in nutrient solution culture

Abstract This study was carried out in order to give some information that could improve spinach nutritional status and productivity. In this paper, the effect of two N forms (N was added either as 100% nitrate or as 80% nitrate and 20% ammonium) and three Fe levels (0 μM Fe; 20 μM FeEDDHA; 3 μM FeEDDHA + 10 mM NaHCO3) on the growth, chlorosis symptoms and shoot nutrient element accumulation was studied in spinach plants (var. Viroflay), grown in hydroponics; six treatments and three harvests (at about 20 days interval each, until plants reached their commercial size) were applied in total. The results indicated that under conditions of Fe sufficiency (20 μM Fe), mixed N nutrition induced higher production of dry matter as well as improved Fe, Mn and Zn plant nutritional status. In plants grown under Fe deprivation (0 μM Fe), shoot Fe concentration was not significantly affected by the N form until the end of the experiment despite mixed N nutrition induced higher dry matter production up to harvest 2; plants grown under Fe deprivation and with mixed N nutrition presented also higher shoot Mn and Zn concentration. Under conditions of high concentration of bicarbonates and low level of Fe (3 μM Fe + 10 mM NaHCO3), the N form had not a significant influence on total dry matter production whereas shoot Fe and Mn accumulation in 100% NO3-fed plants was found to be significantly reduced compared to mixed N nutrition; regardless of the N form, those plants presented the least dry matter production, highest intensity of leaf chlorosis as well as highest root ferric reducing activity compared to plants grown under Fe deprivation.

Estimate of antioxidant capacity and lipid peroxidation in plasma of healthy subjects

Abstract Serum contains various antioxidant molecules that may provide important protection against free radical attack. The aim of this work was to assess the total antioxidant capacity of plasma and a marker of lipid per oxidation [(thiobarbituric acid-reactive substances (TBARS)] in plasma of healthy smoking and non-smoking young and elderly subjects. In addition, we investigated plasma concentrations of α-tocopherol, β-carotene, and ascorbic acid. In in vitro experiments, the effects of exogenous compounds (ascorbic acid, uric acid, Trolox) on total ferric-reducing activity of plasma (FRAP) were also tested. We demonstrated that total antioxidant capacity of plasma obtained from healthy non-smoking young subjects was significantly higher than plasma antioxidant capacity of smoking elderly subjects. The concentration of TBARS in young non-smoking volunteers was lower than that in young smokers. The concentration of TBARS in elderly non-smoking volunteers was lower than in elderly smokers. Plasma concentrations of alpha-tocopherol, beta-carotene and ascorbic acid were significantly lower in elderly smoker than in elderly non-smokers of the same age. No difference in the plasma levels of alpha-tocopherol, beta-carotene and ascorbic acid were found in 22-year-old smoking and non-smoking subjects. In vitro addition of ascorbic acid, uric acid, or Trolox to plasma samples significantly increased their total antioxidant capacity. Decrease of FRAP values and increase of TBARS concentrations is a significant physiologic condition of the aging process. Supplementation of antioxidants could be useful for the enhancement of antioxidant screen in plasma.

Antioxidant capacity and phenolic content of cocoa beans

This study investigated the antioxidant capacity and total phenolic content of cocoa beans from different countries, namely Malaysia, Ghana, Ivory Coast and Sulawesi. The antioxidant capacity of water and ethanolic extracts prepared from cocoa beans was measured by three different assays. To estimate the total phenolic content, the assay using Folin–Ciocalteu reagent was used. The water extract showed the higher value of antioxidant activity based on β-carotene bleaching assay, while the ethanolic extract showed the highest scavenging and ferric reducing activities. Ghanaian cocoa beans showed the highest antioxidant and scavenging activities, followed by Ivory Coast, Malaysian and Sulawesian. However, Malaysian and Sulawesian beans exhibited the highest ferric reducing activity, compared to the other beans. The highest phenolic content was found in Malaysian beans, followed by Sulawesian, Ghanaian and Ivory Coast. A positive correlation existed for both ethanolic ( r = 0.76) and water extracts ( r = 0.78) between phenolic content and ferric reducing activity. Our results showed that antioxidant capacity and phenolic content of Malaysian cocoa beans were comparable to Ghanaian, Ivory Coast, and Sulawesian beans.

Different antioxidants status, total antioxidant power and free radicals in essential hypertension

Hypertension is a multi-factorial process, prevalent in developed as well as in developing countries. Different antioxidants and free radicals play an important role in cardiovascular system. In present study, total antioxidant power in terms of FRAP (ferric reducing activity of plasma), free radicals and different antioxidants have been studied in essential hypertensives (n = 50) and normal subjects (n = 50). Levels of total cholesterol, low-density lipids-cholesterol, malonialdehyde, very low-density lipids (VLDL), uric acid, plasma homocysteine and low-density lipids (LDL), were significantly higher in hypertensives as compared to normotensive. HDL-cholesterol, SOD, GPx, reduced glutahione, total glutathione, oxidized glutathione, total thiols, protein thiols, non protein thiols, RNI, total antioxidant power, vitamin A, ascorbic acid and glutahione-S-transferase (GST) were decreased significantly in normotensive. We observed significantly low nitric oxide levels in hypertensive patients. No correlation was observed between severity of disease and plasma nitric oxide levels. There was a significant decrease in plasma FRAP value in essential hypertensives as compared to normotensive controls, which showed a negative correlation with diastolic blood pressure. In conclusion, our study revealed that there was a consistent significant difference between essential hypertensives versus controls with respect to most of the parameters. These complex changes are consistent in the view that essential hypertension is associated with an abnormal level of antioxidant status compared to normal response to oxidative stress or both.

Analysis of flavonoids and other phenolic compounds using high-performance liquid chromatography with coulometric array detection: relationship to antioxidant activity.

High-performance liquid chromatography coupled with a coulometric array detector was used to characterize the electrochemical behavior of 17 flavonoids and three cinnamic acid derivatives. The antioxidant activity of these phenolic compounds was evaluated by the ferric reducing activity power (FRAP), the oxygen radical absorbance capacity (ORAC), and the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical assays. All flavonoids, except kaempferol-3-rutinoside, malvidin-3-glucoside, and peonidin-3-glucoside, had two oxidation potentials (100-300 and 700-800 mV). Quercetin and myricetin had an additional oxidation wave at 400 mV. The electrochemical responses at a relatively low oxidation potential (300 mV) and the cumulative responses at medium oxidation potentials (400 and 500 mV) had the highest correlations with antioxidant activities. The highest correlations between electrochemical characteristics and antioxidant activities were found between electrochemical responses and antioxidant activities obtained in the FRAP assay and in the DPPH assay after short reaction periods. Lower correlations were revealed between electrochemical responses and antioxidant activities obtained in the ORAC assay.

Antioxidant capacity of bovine milk as assayed by spectrophotometric and amperometric methods

The total antioxidant capacity (TAC) of bovine milk, whey, and low-molecular-weight (LMW) fractions of whey was investigated using spectrophotometric methods including an ABTS-based method (reduction of the cation radical of 2,2′-azinobis(3-ethylenebenzothiazoline-6-sulfonic acid)) and a FRAP method (reduction of Fe3+). Significant antioxidant capacity in milk and whey was demonstrated by the ABTS method (TAC(ABTS)), and it apparently increased with increasing pH. TAC (ABTS) was several-fold higher in milk than in whey, which had a slightly higher TAC than a LMW fraction prepared from it. Also the FRAP method could be used to demonstrate TAC in whey, although the low pH necessary for this method led to some protein precipitation. Most of the ferric-reducing activity of whey was found in the LMW fraction. The TAC values obtained using these methods were also compared to those obtained using a newly developed flow-injection amperometric (FIAmp) procedure for LMW fractions. High correlations were found for the TAC values of LMW samples obtained by the ABTS, FRAP and FIAmp methods (R2>0.8, P<0.001). Furthermore, to identify the major antioxidants in the LMW fraction, it was treated by uricase. Since most of the TAC (using ABTS, FRAP and FIAmp methods) was removed by uricase treatment, it could be concluded that urate is the major antioxidant in the LMW fraction. Also the effect of heat treatment on TAC in milk and whey was monitored. After heating of whey at 63°C for 1 h, TAC(ABTS) tended to increase by at least 20%, while TAC(FRAP) was not significantly changed. In milk, TAC(ABTS) remained constant during the same heat treatment. It is concluded that the methods tested gave the most reliable results for the LMW fraction of whey and that the use of several methods is necessary to characterise the antioxidant capacity of milk.

Plasma concentrations of individual tea catechins after a single oral dose in humans

1. Ten healthy volunteers ingested 1.5 mmole epicatechin gallate (ECg), epigallocatechin (EGC) or epigallocatechin gallate (EGCg) in a randomized crossover design. After deconjugation, catechins in plasma and 24-h urine samples were determined by high-performance liquid chromatography (HPLC). Antioxidant activity was measured in plasma by determining ferric reducing activity (FRAP). 2. The catechin levels in plasma after ingestion were significantly different: EGC rose quickly with a short elimination half-life (t 1/2 elim = 1.7 h), ECg was intermediate in rise but slowest in decline (t 1/2 elim = 6.9h), EGCg was slowest in rise but intermediate in decline (t 1/2 elim = 3.9 h). At 24 h, EGC and EGCg had returned to base levels, but ECg was still elevated. Peak maximum varied between 1.3 (EGCg) and 5.0 µmol l -1 (EGC). 3. Very limited interconversion (ECg → epicatechin, EGCg → EGC) occurred indicating that degallation is not required for uptake. 4. Up to 13.6% of the ingested EGC (partly methylated) was excreted in the urine, but ECg or EGCg were not detected. 5. EGC and ECg produced an increase in antioxidant activity in plasma, but with EGCg, no statistically significant effect was found. 6. The pattern of uric acid in plasma showed a clear resemblance with that of FRAP and linear regression analysis indicated a very significant relationship (R 2 = 0.88, p < 0.0001). 7. It is concluded that tea catechins differ significantly in their pharmacokinetic behaviour.

Ferric and cupric reductase activities in the green alga Chlamydomonas reinhardtii : experiments using iron-limited chemostats

Cells of the green alga Chlamydomonas reinhardtii Dangeard were grown in Fe-limited chemostat culture over a range of growth rates (0.15–1.5 d−1). Greater cell densities and culture chlorophyll levels were achieved using an excess of chelator [ethylenediamine di-(o-hydroxyphenylacetic acid)] relative to FeCl3 (80:1), compared to growth using a 1:1 chelator:FeCl3 ratio. The C. reinhardtii cells reduced extracellular ferric chelates, and ferric chelate reductase activity increased with increasing Fe-limited growth rates. However Fe-sufficient cells exhibited a low rate of ferric chelate reductase activity, similar to severely Fe-limited cells. Iron-limited cells were capable of reducing a wide variety of ferric chelates, representing a wide range of stability constants, at similar rates, suggesting that the stability constants of ferric complexes are not important determinants of ferric reducing activity. Cupric reductase activity also increased with increasing Fe-limited growth rates, and Cu(II) was preferentially reduced compared to Fe(III). These results suggest that both reductase activities may represent the same plasma-membrane enzyme. The rate of cupric reduction was a function of the free [Cu2+], not the total [Cu(II)], suggesting that free Cu2+ is the actual substrate for cupric reductase activity.

The ferric-reducing activity of duodenal brush-border membrane vesicles is associated with a b-type haem.

Rabbit brush-border membrane vesicles possess ferricyanide reducing activity. This activity is preferentially dependent on NADH as reductant, and can be stimulated by the addition of FMN. The latency of activity observed following vesicle solubilisation suggests that the responsible component is transmembranous, and partially sequestered on the inner-face of the vesicles prior to full solubilisation. Subsequent increases in detergent concentration (> 0.3% w/v lauryl maltoside) were found to be inhibitory. Ferricyanide reducing activity was effectively inhibited by the sulphydryl modifying reagents N-ethyl malemide and p-chloromercuribenzoate, but not by the flavin analogue diphenylene iodonium. The ferric-reducing activity co-purified with a b-type haem when applied to Sephacryl S-200 columns. The putative cytochrome was found to be immunologically distinct from neutrophil cytochrome b558.

Ferric pseudobactin 358 as an iron source for carnation

Abstract The influence of the siderophore produced by plant growth‐promoting Pseudomonas putida strain WCS358, pseudobactin 358 (PSB358), on chlorophyll synthesis and iron(III) reduction in carnation cultivars Lena and Pallas grown in hydroponics was studied. Ferric pseudobactin 358 (4 μM) stimulated chlorophyll synthesis in cv. Lena, but not in cv. Pallas. FeEDDHA stimulated chlorophyll synthesis in both cultivars. Differences between the two carnation cultivars in the utilization of FePSB358 as an iron source are correlated with differences in iron efficiency reactions of the two cultivars: Fe‐deficient plants of cv. Lena produced more and longer root hairs than Fe‐deficient plants of cv. Pallas, and the ferric reducing activity of cv. Lena was higher than that of cv. Pallas.

Iron-Deficiency Stress Responses in Cucumber (Cucumis sativus L.) Roots (A Possible Role for Ethylene?).

Most dicotyledonous species respond to Fe deficiency by developing several mechanisms known as Fe-deficiency stress responses. To study the regulation of these responses, young cucumber plants (Cucumis sativus L. cv Ashley) were grown in nutrient solution for 11 d, being deprived of Fe during the last 4 or 5 d. Inhibitors of ethylene synthesis (2 or 10 [mu]M aminoethoxyvinylglycine; 10 or 20 [mu]M aminooxyacetic acid; 1, 2, 5, or 10 [mu]M Co2+ as CoCl2) or action (50, 200, or 800 [mu]M Ag+ as silver thiosulfate) were added to the nutrient solution at different times during this period of growth with no Fe. After this period, the reduction of Fe3+ ethylenedi-aminetetraacetate by the roots of entire plants was measured with ferrozine by reading the absorbance at 562 nm after 2 h. The presence of the ethylene inhibitors in the nutrient solution inhibited the Fe-deficiency stress responses ferric-reducing capacity and subapical root swelling. In another experiment, the addition of 1 [mu]M 1-aminocyclopropane-1-carboxylic acid (ACC), a precursor of ethylene synthesis, to the nutrient solution of plants having low ferric-reducing activity increased notably the ferric-reducing capacity and subapical root swelling. Here we show evidence that ethylene plays a role in the development of Fe-deficiency stress responses, since when ethylene synthesis or action was inhibited, the responses were also inhibited, and when a precursor of ethylene (ACC) was added, the responses were increased.

Anaerobic growth on elemental sulfur using dissimilar iron reduction by autotrophicThiobacillus ferrooxidans

Anaerobic growth on elemental sulfur using dissimilar iron reduction by Thiobacillus ferrooxidans has been demonstrated. The ferric ion reducing activity (FIR) of the anaerobic cells was double that of the aerobic cells. Significant differences in inhibition of FIR by respiratory inhibitors were observed between aerobic and anaerobic cells. A higher amount of cytochrome was detected in anaerobic cells compared to aerobic cells. Absorption minima developed with the addition of ferric sulfate in the dithionite reduced cell suspension demonstrated that the ferric ion could accept electrons from the cytochrome system of this bacterium. The possibility of two different electron transport chains in ferric ion reduction is discussed.

Anaerobic growth on elemental sulfur using dissimilar iron reduction by autotrophic Thiobacillus ferrooxidans

Anaerobic growth on elemental sulfur using dissimilar iron reduction by Thiobacillus ferrooxidans has been demonstrated. The ferric ion reducing activity (FIR) of the anaerobic cells was double that of the aerobic cells. Significant differences in inhibition of FIR by respiratory inhibitors were observed between aerobic and anaerobic cells. A higher amount of cytochrome was detected in anaerobic cells compared to aerobic cells. Absorption minima developed with the addition of ferric sulfate in the dithionite reduced cell suspension demonstrated that the ferric ion could accept electrons from the cytochrome system of this bacterium. The possibility of two different electron transport chains in ferric ion reduction is discussed.

Ferric Reducing Activity in Roots of Fe-deficient Phaseolus vulgaris Source of Reducing Equivalents

Summary Fe deficiency activates a system in the roots of dicotyledons which can reduce extracellular ferric chelates (ferric reductase); this system is located in the plasma membranes of the epidermal cells. In order to identify the source of reducing equivalents for the reduction of ferric chelates by roots of bean ( Phaseolus vulgaris L. var. Prelude), properties of NADP + reducing enzymes were studied and incubations were performed with glucose labeled with 14 C at positions Cl and C6. NADP-dependent isocitrate dehydrogenase was the most active of the enzymes tested in root protein extracts and it could reduce NADP+ even at very high NADPH/NADP + ratios. It is concluded that citrate, which accumulates in roots upon Fe deficiency, via transformation into isocitrate by mitochondrial aconitase, drives cytosolic NADP in bean roots to a strongly reduced state through isocitrate dehydrogenase. Upon addition of reducible ferric salts, the NADP couple becomes more oxidized making it possible for the oxidative pentose phosphate pathway to contribute to NADP + reduction.

Characterization of ferric reducing activity in roots of Fe‐deficient Phaseolus vulgaris

Iron‐deficient bean plants (Phaseolus vulgaris L. cv. Prélude) exhibited a ferric reducing activity in the roots, with kinetics characteristic for matrix‐bound enzymes: the reaction rate was proportional to substrate (Fe‐EDTA) concentration until 100 μM, and at higher concentrations it leveled off to a maximum; the Lineweaver‐Burk plot yielded a non‐linear relationship between rate −1 and substrate −1. The Arrhenius plot yielded apparent activation energies which were dependent on substrate concentration. No evidence was obtained for the secretion by roots of a low molecular weight metabolite involved in the reduction of iron prior to its uptake. The results are interpreted to indicate that the ferric reducing activity in the roots of iron‐deficient bean plants is located in an enzyme in the plasmalemma of the cortex or epidermis cells.