Nitrogen,phosphorus and potassium in Salvinia molesta Mitchell in the field: effects of weather,insect damage,fertilizers and age

More than 1700 samples of Salvinia molesta Mitchell were collected from sites distributed from close to the equator in Papua New Guinea to 33°S in Australia. Nitrogen content ranged from 0.62 to 4.0% dry weight, phosphorus from 0.03 to 1.07% and potassium from 0.31 to 5.32%. Tops contained more concentrated N and P than roots, while K was more concentrated in roots. Concentrations of N and P were significantly correlated.Rainfall, followed by runoff, resulted in peaks of N, P and K in plants in one lake, but the sequence could not be demonstrated at other sites. At sites experiencing marked seasonal changes in temperature, N and P contents were inversely correlated with temperature, probably due to greater growth and utilisation of nutrients in summer. Damage caused by the biological control agent Cyrtobagous salviniae Calder and Sands decreased K content, while N and P contents were increased in some cases, but not in others. Thick mats of S. molesta in Papua New Guinea contained less concentrated N and P than thin mats, but this was not necessarily the case in the Australian sites. The reasons for these differences, and the likely effects on biological control agents, are discussed.Urea and superphosphate were found to increase N and P concentrations in the plant by amounts useful for experimental purposes and for aiding establishment of biological control agents. An equation related N concentration to the amount of urea applied and background N content of the plant. Concentrations of N, P and K decreased with age. Levels of N and P dropped most quickly as buds opened, then dropped slowly until the onset of senescence caused another rapid decline. The implications of these changes for insects feeding on S. molesta are discussed.     

Die küstenvegetation ostkanadas: D. Thannheiser. Münstersche Geographische Arbeiten. No. 10. Schöningh,Paderborn, 1981, 201 pp. 166 figs., 41 tables,DM. 41.50. ISBN 3-506-73210-2

Temperatures 10 and 2 cm above water level, in leaves of Salvinia molesta Mitchell, and 2 and 10 cm below water level, were measured in the field at hourly intervals over a total of 125 days. Temperature cycles of leaves and air had mean diurnal amplitudes of 8°C in summer and 17°C in winter; cycles in water lagged behind and had amplitudes which decreased with depth. Most parts of S. molesta were warmer than the air at a nearby weather station most of the time and there was temperature stratification in the water during the warm part of each day.Standard meteorological variables were selected, using stepwise regression, to predict daily maximum and minimum temperatures of S. molesta. Thermal inertia of water in the lake seemed to elevate S. molesta temperatures in autumn and depress them in spring compared with temperatures at the weather station. Better predictors were obtained by adding to meteorological variables a function based on the annual cycle of temperatures 10 cm below water level. Hourly temperatures experienced by S. molesta were predicted using curves fitted to diurnal cycles. The reliability of predictions was tested for each season of the year with independent data for a total of 78 days. Predicted temperatures were close to observed temperatures both in absolute terms and in terms of temperature-dependent growth rates of S. molesta.     

Influence of <Emphasis Type="Italic">Potamogeton crispus</Emphasis> growth on nutrients in the sediment and water of Lake Tangxunhu

An incubation experiment was performed on Potamogeton crispus (P. crispus) using sediment collected from Lake Tangxunhu in the center of China, in order to determine the effects of plant growth on Fe, Si, Cu, Zn, Mn, Mg, P, and Ca concentrations in the sediments and overlying waters. After 3 months of incubation, Ca, Mg, and Si concentrations in the water column were significantly lower, and P and Cu concentrations were significantly higher than in unplanted controls. The effect of P. crispus growth on sediment pore waters and water-extractable elements varied. Concentrations of Ca, Mg, Si, Fe, Cu, and Zn were significantly higher, and P was significantly lower, than in pore waters of the control. Water-extracted concentrations of Fe, Mg, and Si in the sediments were lower, and P was higher, than in the control. Presence of P. crispus generally enhanced concentration gradients of elements between pore waters and overlying waters but not for P. The growth of P. crispus was associated with an increase in water pH and formation of root plaques, resulting in complex effects on the sediment nutritional status. Handling editor: S. M. Thomaz     

Direct electrochemical oxidation of Clostridium pasteurianum ferredoxin: Identification of facile electron-transfer processes relevant to cluster degradation

Rapid oxidation processes relevant to the degradation of [4Fe4S] clusters in Clostridium pasteurianum ferredoxin were studied via direct (unmediated) heterogeneous electron transfer at a pyrolytic graphite electrode. Differential-pulse voltammograms of native [4Fe4S] ferredoxin showed two well-defined oxidation peaks corresponding to apparent E-values of +793 and +1120 mV at 5°C. Direct involvement of the cluster was established through parallel experiments with the 2[4Fe4Se] derivative for which peak positions were shifted. Square-wave voltammetry showed that the product of the first electron transfer, which may correspond to the ‘super-oxidised’ [4Fe4S]³⁺ oxidation level, undergoes rapid degradation (t_{$\text{1}\text{2}$} < 1.6 ms at 5°C). The second oxidation process, as characterised by a significant (?100 mV) negative shift upon selenium substitution, very likely represents oxidation of S(Se) still associated with the protein and possibly contained within the remaining FES(Se) substructure.     

Main group metal halide complexes with sterically hindered thioureas. IX. New complexes of selected post-transition metals and 1,3-dimethyl-2(3H)-imidazolethione and a structural investigation of infrared peak shifts associated with coordination

Five new complexes of sterically hindered 1,3- dimethyl-2(3H)-imidazolethione (dmit) with the chlorides of Cd(II), Hg(II), Te(II), Sn(IV) and Sb(V) have been synthesized and characterized. The previously reported Zn(II) adduct was also synthesized and further characterized. These complexes were of the general formula MX_n(dmit)_m where n = 2 and m = 2 when M = Zn, Cd, Hg and Sn; and n = 2 and m = 4 for Te(II). The only 1:1 adduct observed was SbCl₅dmit, and its chemistry is more complex giving rise to unique redox products upon heating in solution. Solid state spectra of these complexes as well as for dmit complexes are reported and discussed with regard to the coordination sensitive NCN asymmetric stretch and the CS stretch observed not only for dmit complexes but for tetramethylthiourea (tmtu) complexes reported in the literature as well. Greatest shifts on coordination are observed with the NCN asymmetric stretch for tmtu causing shifts to higher wave numbers ranging from 55 to 95 cm⁻¹ relative to free tmtu. Shifts are explained on the basis of observed crystal structures of tmtu adducts showing a greater CN double bond character. Dmit adducts show much smaller shifts both to higher and lower wave numbers for this mode relative to free ligand, and the CS stretch shows little change also. Comparison to known crystal structures show little change in the bond distances of the dmit ligand upon coordination. Inductive effects based on correlations of shift magnitude to the Sanderson group electronegativity (SGEN) of the acceptor seem to be unrelated with the exception of a small positive correlation observed for the NCN asymmetric stretch of tmtu.     

Elemental distribution in tissue components of N2-fixing nodules of Psoralea pinnata plants growing naturally in wetland and upland conditions in the Cape Fynbos of South Africa

There is little information on in situ distribution of nutrient elements in N₂-fixing nodules. The aim of this study was to quantify elemental distribution in tissue components of N₂-fixing nodules harvested from Psoralea pinnata plants grown naturally in wetland and upland conditions in the Cape Fynbos. The data obtained from particle-induced X-ray emission revealed the occurrence of 20 elements (Si, P, S, Cl, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn, As, Br, Rb, Sr, Y, Zr, Mo and Ba) in nodule components. Although, in upland plants, the concentrations of S, Fe, Si, Mn and Cu showed a steady increase from the middle cortex to the medulla region of P. pinnata nodules, in wetland plants, only S, Fe and Mn showed an increase in concentration from the middle cortex to the bacteria-infected medulla of P. pinnata nodules. By contrast, the concentrations of Cl, K, Ca, Zn and Sr decreased from middle cortex to nodule medulla. The alkaline earth, alkali and transition elements Rb, Sr, Y and Zr, never before reported in N₂-fixing nodules, were found to occur in root nodules of P. pinnata plants grown in both wetland and upland conditions.     

Oxygen and nitric oxide affinities of iron(II) ‘capped’ porphyrins

Oxygen and NO binding constants are reported for Fe(Por)(B) [1] complexes. The results show a good correlation between O₂ and NO affinities, and this is attributed to the similar bent structures of the FeOO and FeNO moieties. Evidence is presented to show that iron(II) C₃-capped porphyrins have a low affinity for O₂ because of ligand coordination on the cavity side of the cap.     

The crystal and molecular structures of dioxo mo(VI) complexes of tripodal,tetradentate N,S-donor ligands

The crystal and molecular structures of the complexes MoO₂((SCH₂CH₂)₂NCH₂CH₂SCH₃), I and MoO₂((SCH₂CH₂)₂NCH₂CH₂N(CH₃)₂), II, have been determined from X-ray intensity data collected by counter methods. Compound I crystallizes in two forms, Ia and Ib. In form Ia the space group is P2₁/n with cell parameters a = 7.235(2), b = 7.717(2), c = 24.527(6) Å, β = 119.86(2)°, V = 1188(1) ų, Z = 4. In form Ib the space group is P2₁/c with cell parameters a = 14.945(5), b = 11.925(5), c = 14.878(4) Å, β = 114.51(2)°, V = 2413(3) ų, Z = 8. The molecules of I in Ia and Ib are very similar having an octahedral structure with cis oxo groups, trans thiolates (cis to both oxo groups) and N and thioether sulfur atoms trans to oxo groups. Average ditances are MoO = 1.70, MoS (thiolate) = 2.40, MoN = 2.40 and MoS (thioether) = 2.79 Å. Molecule II crystallizes in space group P2₁2₁2₁ with a = 7.188(1), b = 22.708(8), c = 7.746(2) Å, V = 1246(1) ų and Z = 4. The coordination about Mo is octahedral with cis oxo groups, trans thiolates and N atoms trans to oxo. Distances in the first coordination sphere are MoO = 1.705(2), 1.699(2), MoS = 2.420(1), 2.409(1) and MoN = 2.372(2), 2.510(2) Å. The conformational features of the complexes are discussed. Complex I displays MoO and MoS distances which are very similar to those found by EXAFS in sulfite oxidase. This similarity is discussed.     

Plant communities of extreme acidic waters: The Rio Tinto case

As one of the largest extreme acidic environments in the world the Río Tinto (Spain) constitutes a useful case to study the vegetation resistant to waters, sediments and soils with pH < 3 and high concentrations of S, Fe, Cu and other metals. In this territory two types of water courses coexist: the extreme acidic waters, with a low pH and high amounts of S and Fe, usually of a red color, and those that are not extremely acid, which include colorless acid, neutral and basic waters with much less S and Fe. An exhaustive study of the riparian vegetation present along the two first sections of the Río Tinto and in less extreme, neighboring water courses was carried out (61 inventories). Some water quality variables (pH, redox, Fe, Cu and O₂) were measured in sampled points. Correspondence between plant community composition and water quality was analyzed through hierarchical classification, detrended correspondence analysis and canonical correspondence analysis.Results indicate clear differences in vegetation between extremely acidic and less extreme water courses. A total of 50 emergent plant species have been found in extremely acidic waters. Among them the most frequent were Erica andevalensis Cabezudo and J. Rivera, Scirpoides holoschoenus (L.) Soják and Nerium oleander L. Additionally, pH, redox, Fe and O₂ concentrations were significantly related to the floristic data.     

Rhizobium population genetics: Effect of clover variety and inoculum dilution on the genetic diversity sampled from natural populations

Concentrations of N, P and K were measured in floodwater and in floating rice cultivars growing at up to 2m water depths in the central flood plain of Thailand. Concentrations of N, P and K in floodwater were often higher than those reported for oligotrophic lakes, nevertheless the floodwater contained 4–45 times less K and 15–90 times less N than concentrations reported in most soil solutions. P concentrations were similar in the floodwater and in most soil solutions. Concentrations of nutrients in leaves indicated there may be deficiencies of P at two sites and a deficiency of N at one of two sites. Data are discussed in terms of reduced nutrient uptake in rice fields at low O₂ concentrations which have recently been measured in these areas.     

Sulfate control of phosphorus availability in lakes

During summer stratification large amounts of phosphorus (P) accumulate in anoxic bottom waters of many lakes due to release of P from underlying sediments. The availability to phytoplankton of this P is inversely related to the Fe:P ratio in bottom waters. Using data from 51 lakes, we tested the hypothesis that sulfate concentration in lake water may be critical in controlling the Fe:P ratio in anoxic bottom waters. Results showed that Fe:P ratios in bottom waters of lakes were significantly (p<0.001) related to surface water sulfate concentrations. The higher Fe:P ratios in low sulfate systems is due not only to higher iron concentrations in anoxic bottom waters but also to lower P concentrations in anoxic waters. Thus, our results suggest that anthropogenically induced increases in sulfate concentrations of waters (e.g. from fossil fuel burning) may have a double effect on P cycling in lakes. Higher sulfate concentrations can both increase the magnitude of P release from sediments as well as increase the availability of P released from sediments into anoxic bottom waters.     

Samea multiplicalis [Lep.: Pyralidae], for biological control of two water weeds,Salvinia molesta andPistia stratiotes in Australia

The biology and host specificity ofSamea multiplicalis (Guenée) were studied in quarantine in Australia. Immature stages completed development onSalvinia molesta Mitchell,Pistia stratiotes L. andAzolla pinnata R.Br. In starvation tests, although larvae which had first fed onS. molesta produced minor leaf scarring on some other plants, they were unable to complete development. Damage toS. molesta andP. stratiotes indicated thatS. multiplicalis may be a valuable biological control agent for these weeds in Australia.S. multiplicalis was first liberated in northern Queensland in 1981 where it has become established onS. molesta.     

Structure-function relationship of [2Fe2S] ferredoxins and design of a model molecule

[2Fe2S] ferredoxins isolated from various plants and algae comprise 93–99 amino acid residues and resemble each other not only in sequences, but also in physiological functions. One of them isolated from Spirulina platensis was subjected to X-ray analysis and its three dimensional structure is now known. [2Fe2S] ferredoxins of a different type are found in halobacteria and comprise 128 amino acid residues. Both types of the [2Fe2S] ferredoxins exhibit low redox potentials. By comparing the amino acid sequences of 28 [2Fe2S] ferredoxins and the tertiary structure of S. platensis ferredoxin we predicted a common three-dimensional structure to the [2Fe2S] ferredoxins and proposed a molecular surface area to be interacting with FNR. An artificial small molecule composed of 20 amino acid residues is designed on the basis of the tertiary structure of S. platensis ferredoxin. The amino acid sequence was predicted to be ProTyrSerCysArgAlaGlyAlaCysSerThrCysAlaGly ProLeuLeuThr CysVal which should have a [2Fe2S] cluster with a low redox potential     

Growth response of Microcystis spp. to iron enrichment in different regions of Lake Taihu, China

Iron (Fe) is an essential micronutrient for algal growth and can be a potential limiting nutrient in aquatic system, especially regions that exhibits nitrogen (N) limitation. Using short-term nutrient addition bioassays, we evaluated the potential role that iron might play in modifying the response of Microcystis spp. to the anthropogenic phosphorus (P) and N enrichment in hypereutrophic Lake Taihu, the third largest freshwater lake in China. Three nutrient enrichment experiments involving additions of N (as NO₃ ^?) and P (as PO₄ ^3?) with and without Fe were conducted during 2009?C2010 in Meiliang Bay, a region characterized by summer cyanobacterial (Microcystis spp.) blooms, and East Taihu, a region largely free of cyanobacterial blooms and dominated by macrophytes. In Meiliang Bay, Fe addition alone did not significantly increase Microcystis spp. biomass. However, Fe addition occasionally increased the stimulatory effect of N and P additions on Microcystis spp., indicating that Fe was not a primary limiting nutrient for Microcystis spp. growth. Occasionally Fe was co-limiting with N and P in this region. In East Taihu, the addition of Fe alone significantly stimulated Microcystis spp. growth, while addition of N and/or P had no effects on growth, indicating that Fe was a primary limiting nutrient in East Taihu. The combined addition of Fe and N resulted in a growth response similar to Fe alone, while combined addition of Fe and P yielded greater biomass increases than the addition of Fe alone. This indicated that in East Taihu, N was not limiting and Fe and P supplies facilitated Microcystis spp. growth. These results reflect differential availabilities and limitations of N, P, and Fe in distinct regions of Taihu. The potential role of Fe in eutrophication dynamics of large, regionally complex lakes like Taihu requires further attention.     

Growth of a floating aquatic weed,Salvinia under standard conditions

1. Growth of the floating aquatic weed, Salvinia, in sterile culture was exponential for at least 2 weeks under standardized conditions.
2. Increase in light intensity or in CO₂ resulted in increases in growth rate, but did not extend the exponential period of growth.
3. This aquatic plant, like many others, discriminates against calcium relative to strontium.
4. In culture Salvinia exhibited luxury consumption of N and P.
5. Because of high C/N ratios, Salvinia may not be a favorable source of animal food, but might be useful in nutrient removal schemes.
6. In sterile culture, S. molesta produced fewer leaves than S. minima, but maintained a significant increase in leaf area and dry weight. This may be correlated with the ability of the first species to rapidly spread over tropical waterways.

     

茎瘤芥不同生长期植株营养特性及其与产量的关系

在涪陵区选取30个茎瘤芥种植农户,采用大田调查和室内化学分析方法,研究了茎瘤芥不同生长期（苗期、快速膨大期、采收期）叶片和茎瘤10种必需营养元素含量的变化特征及其与产量的关系。结果表明：茎瘤芥在整个生育期内,除K、S含量较高外,其余大、微量元素均在大多植物含量范围内;不同生育期茎瘤芥叶片、茎瘤中各养分含量变化具有明显的规律性,苗期叶片大量元素含量次序为N>K>Ca>P>S>Mg,快速膨大期和采收期叶片大量元素含量次序均为N>K>Ca>S>P>Mg,茎瘤中大量元素含量次序均为K>N>P>S>Ca>Mg,3个生长期叶片和茎瘤的微量元素含量,除快速膨大期茎瘤中略有不同（Fe>Zn>Mn>Cu）外,其余均为Fe>Mn>Zn>Cu;从苗期到快速膨大期再到采收期养分变化规律看,叶片中N、P、K、Fe、Cu和Zn含量呈降低趋势,而Ca、Mg、S和Mn则呈现先降低后升高的趋势,从快速膨大期到采收期茎瘤中除N、S、Fe和Cu元素呈降低趋势外,其余养分元素均呈上升趋势。从茎瘤芥不同器官养分含量高低看,快速膨大期和采收期叶片中N、P、K、Cu和Zn含量较茎瘤中低,而Ca、Fe和Mn含量的变化特点则相反,S和Mg差异较小,表明茎瘤芥不同部位对不同养分的敏感程度各异。相关分析表明,各生育期不同器官的Mg、Fe、Mn和Zn与产量呈显著或极显著的负相关关系,K、Cu与产量呈正的相关关系。通过逐步回归分析建立茎瘤芥各生育期植株营养元素与产量的回归预测模型,其中苗期叶片营养元素与产量的最优回归方程为Y= 36768 3583XK-6.328XFe-76.09XMn;快速膨大期叶片和茎瘤营养元素与产量的最优回归方程分别为Y=50458 21557XP 7925XCa-88092XMg-1145XCu和Y=32487 7294XK-116122XMg;采收期叶片和茎瘤营养元素与产量的最优回归方程分别为Y=36064 3413XK-30.15XFe和Y= 11791 7334XK-385XZn。因此,在茎瘤芥各生长期均应注意钾肥的合理施用,快速膨大期应重视磷肥的施用。而几种微量元素和镁素对茎瘤芥产量的负效应,则可通过增施充分腐熟的有机肥料加以调控。     

RETRACTED ARTICLE: CO<Subscript>2</Subscript> effects on plant nutrient concentration depend on plant functional group and available nitrogen: a meta-analysis

Elevated CO₂ is expected to lower plant nutrient concentrations via carbohydrate dilution and increased nutrient use efficiency. Elevated CO₂ consistently lowers plant foliar nitrogen, but there is no consensus on CO₂ effects across the range of plant nutrients. We used meta-analysis to quantify elevated CO₂ effects on leaf, stem, root, and seed concentrations of B, Ca, Cu, Fe, K, Mg, Mn, P, S, and Zn among four plant functional groups and two levels of N fertilization. CO₂ effects on plant nutrient concentration depended on the nutrient, plant group, tissue, and N status. CO₂ reduced B, Cu, Fe, and Mg, but increased Mn concentration in the leaves of N₂ fixers. Elevated CO₂ increased Cu, Fe, and Zn, but lowered Mn concentration in grass leaves. Tree leaf responses were strongly related to N status: CO₂ significantly decreased Cu, Fe, Mg, and S at high N, but only Fe at low N. Elevated CO₂ decreased Mg and Zn in crop leaves grown with high N, and Mn at low N. Nutrient concentrations in crop roots were not affected by CO₂ enrichment, but CO₂ decreased Ca, K, Mg and P in tree roots. Crop seeds had lower S under elevated CO₂. We also tested the validity of a “dilution model.” CO₂ reduced the concentration of plant nutrients 6.6% across nutrients and plant groups, but the reduction is less than expected (18.4%) from carbohydrate accumulation alone. We found that elevated CO₂ impacts plant nutrient status differently among the nutrient elements, plant functional groups, and among plant tissues. Our synthesis suggests that differences between plant groups and plant organs, N status, and differences in nutrient chemistry in soils preclude a universal hypothesis strictly related to carbohydrate dilution regarding plant nutrient response to elevated CO₂.     

Metalloproteins in the evolution of photosynthesis

Certain metalloproteins are common to all photosynthetic electron transfer chains. These include soluble proteins such as ferredoxins and cytochromes of the c₂ type, and membrane-bound components such as cytochrome b, c₁ and the Rieske iron-sulphur protein. The sequence of electron transfer Quinone → (cyt b, FeS, cyt c₁) → cyt c₂ indicates a common precursor to these systems and to the mitochondrial respiratory chain. In cyanobacteria the cytochrome c₁, can be interchanged with the copper protein plastocyanin, and furthermore in chloroplasts of higher plants the latter is used exclusively. The ferredoxins in anaerobic photosynthetic bacteria are mostly of the [4Fe4S] type, probably derived from those of the fermentative bacteria. These could readily be formed in the earliest cells from iron, sulphide and a very simple peptide. In the oxygen-evolving cyanobacteria and the aerobic halobacteria the [2Fe2S] ferredoxins predominate. The electron transfer chains of the cyanobacteria have been incorporated almost unchanged into the chloroplasts of plants. The electron transfer chains of purple photosynthetic bacteria were probably the precursors of the mitochondrial respiratory chain, as shown by similarities of cytochromes c₂ and succinate dehydrogenase. However a different origin of the eukaryotic cytoplasm is indicated by the presence of the copper/zinc superoxide dismutase.     

Nutrient cycling and productivity in a desert saline lake: observations from a dry,low-productivity year

Seasonal variability of nutrients and productivity were examined in Pyramid Lake, a hyposaline, N-deficient, terminal desert lake, during a dry period. River inflow and N-fixation during 1990 were minimal allowing internal nutrient cycling to be more closely studied. Nutrient cycling was strongly affected by seasonal thermal stratification that was typical for a warm monomictic lake. Concentrations of nitrate, phosphate, and silicate in surface waters were highest during winter mixing and decreased rapidly in the spring due to a diatom bloom. Maximum average chlorophyll concentration in surface waters was 2.7 ± 1.2 µg 1^–1 and occurred in April while surface nutrients were being depleted. In contrast to chlorophyll, maximum particulate carbon in surface waters occurred in July–August when areal productivity was highest (367–398 mg C m^–2 day^–1). Concurrent with spring nutrient depletion in surface waters was increasing N-deficiency in the plankton. After the spring bloom dissipated in May, particulate matter (POM) became increasingly N-deficient reaching maximum elemental C : N of > 18 during summer-fall. Profiles of the C : N ratio of POM were nearly constant with depth for individual sampling dates suggesting that the residence time of POM in the water column was short (< 1 month). While surface waters were nutrient depleted during summer stratification, nutrient concentrations of bottom waters progressively increased, presumably through the oxidation of POM sinking to the bottom (103 m). Converting the rate of oxygen depletion in bottom waters to carbon equivalents of POM suggests that 42 % of mean annual phytoplankton production in overlying waters during 1990 was mineralized in bottom waters.     

Primary structure of a 7Fe ferredoxin from Streptomyces griseus

The complete primary structure of a Streptomyces griseus (ATCC 13273) 7Fe ferredoxin, which can couple electron transfer between spinach ferredoxin reductase and S. griseus cytochrome P-450_soy for NADPH-dependent substrate oxidation, has been determined by Edman degradation of the whole protein and peptides derived by Staphylococcus aureus V8 proteinase and trypsin digestion. The protein consists of 105 amino acids and has a calculated molecular weight, including seven irons and eight sulfurs, of 12291. The ferredoxin sequence is highly homologous (73%) to that of the 7Fe ferredoxin from Mycobacterium smegmatis. The N-terminal half of the sequence, which is the FeS clusters binding domain, has more than 50% homology with other 7Fe ferredoxins. In particular, the seven cysteines known from the crystal structure of Azotobacter vinelandii ferredoxin I to be involved in binding the two FeS clusters are conserved.