Design of a Superpositively Charged Enzyme: Human Carbonic Anhydrase II Variant with Ferritin Encapsulation and Immobilization.

Supercharged proteins exhibit high solubility and other desirable properties, but no engineered superpositively charged enzymes have previously been made. Superpositively charged variants of proteins such as green fluorescent protein have been efficiently encapsulated within Archaeoglobus fulgidus thermophilic ferritin (AfFtn). Encapsulation by supramolecular ferritin can yield systems with a variety of sequestered cargo. To advance applications in enzymology and green chemistry, we sought a general method for supercharging an enzyme that retains activity and is compatible with AfFtn encapsulation. The zinc metalloenzyme human carbonic anhydrase II (hCAII) is an attractive encapsulation target based on its hydrolytic activity and physiologic conversion of carbon dioxide to bicarbonate. A computationally designed variant of hCAII contains positively charged residues substituted at 19 sites on the protein's surface, resulting in a shift of the putative net charge from -1 to +21. This designed hCAII(+21) exhibits encapsulation within AfFtn without the need for fusion partners or additional reagents. The hCAII(+21) variant retains esterase activity comparable to the wild type and spontaneously templates the assembly of AfFtn 24mers around itself. The AfFtn-hCAII(+21) host-guest complex exhibits both greater activity and thermal stability when compared to hCAII(+21). Upon immobilization on a solid support, AfFtn-hCAII(+21) retains enzymatic activity and exhibits an enhancement of activity at elevated temperatures.

Label-free approach for electrochemical ferritin sensing using biosurfactant stabilized tungsten disulfide quantum dots.

A novel approach for the synthesis of biosurfactant stabilized/functionalized tungsten disulfide (WS2-B) quantum dots (QDs) and its application for ferritin immunosensor is reported. These 2-D layered material derived quantum dots are synthesized via one-step liquid exfoliation method and biosurfactant was used as a functionalization and stability providing moiety. The biosurfactant provided a clean and green method for both the synthesis and in-situ functionalization of the QDs. Exhaustive characterization using analytical techniques was done to study various aspects of the synthesized quantum dots. The functionalized quantum dots (WS2-B QDs) were further explored for their possible application as an electroactive platform. For this, the working area of commercially available screen-printed electrodes (SPE) was functionalized with these WS2-B QDs to construct a sensor platform. This sensor platform was then used for fabrication of ferritin immunosensor, using ferritin specific antibodies. Cyclic Voltammetry (CV) and Differential Pulse Voltammetry (DPV) techniques were used for electrochemical immunosensing of ferritin. Though, the achieved linear range for ferritin detection (10-1500 ng mL-1) is same with both the techniques but regression coefficient and limit of detection are better in differential pulse voltammetry. The limit of detection was found to be 3.800 ng mL-1 in DPV and 6.048 ng mL-1 in CV. The immunosensor is highly selective, reproducible and is stable for about 60 days.

Routes of iron entry into, and exit from, the catalytic ferroxidase sites of the prokaryotic ferritin SynFtn.

Ferritins are multimers comprised of 4 α-helical bundle monomers that co-assemble to form protein shells surrounding an approximately spherical internal cavity. The assembled multimers acquire Fe2+ from their surroundings by utilising channels that penetrate the protein for the transportation of iron to diiron catalytic centres buried within the monomeric units. Here oxidation of the substrate to Fe3+ is coupled to the reduction of O2 and/or peroxide to yield the precursor to a ferric oxy hydroxide mineral that is stored within the internal cavity. The rhombic dodecahedral quaternary structure results in channels of 4-fold and 3-fold symmetry, located at the vertices, which are common to all 24mer-ferritins. Ferritins isolated from higher eukaryotes have been demonstrated to take up Fe2+via the 3-fold channels. One of the defining features of ferritins isolated from prokaryotes is the presence of a further 24 channels, the B-channels, and these are thought to play an important role in Fe2+ uptake in this sub-family. SynFtn is an unusual ferritin isolated from the marine cyanobacterium Synechococcus CC9311. The reported structure of SynFtn derived from Fe2+ soaked crystals revealed the presence of a fully hydrated Fe2+ associated with three aspartate residues (Asp137 from each of the three symmetry related subunits) within each three-fold channel, suggesting that it might be the route for Fe2+ entry. Here, we present structural and spectro-kinetic data on two variants of SynFtn, D137A and E62A, designed to assess this possibility. Glu62 is equivalent to residues demonstrated to be important in the transfer of iron from the inner exit of the 3-fold channel to the catalytic centre in animal ferritins. As expected replacing Asp137 with a non-coordinating residue eliminated rapid iron oxidation by SynFtn. In contrast the rate of mineral core formation was severely impaired whilst the rate of iron transit into the catalytic centre was largely unaffected upon introducing a non-coordinating residue in place of Glu62 suggesting a role for this residue in release of the oxidised product. The identification of these two residues in SynFtn maps out major routes for Fe2+ entry to, and exit from, the catalytic ferroxidase centres.

Impact of Phosphate on Iron Mineralization and Mobilization in Nonheme Bacterioferritin B from Mycobacterium tuberculosis.

Ferritins are supramolecular nanocage proteins, which synthesize hydrated ferric oxyhydroxide mineral via protein mediated rapid Fe2+ sequestration and ferroxidase reactions. Ferritin minerals are also associated with a significant amount of phosphate, which contribute toward their structure and reactivity. Like iron, phosphate also regulates the pathogenesis of Mycobacterium tuberculosis (Mtb), which expresses two types of ferritin: heme binding bacterioferritin A (BfrA) and nonheme binding bacterioferritin B (BfrB). Unlike Mtb BfrA, the rapid kinetics and mechanism of ferroxidase activity, and the mineral core formation/dissolution in Mtb BfrB are not well explored. Moreover, the effect of physiological levels of phosphate (0-10 mM) on the synthesis, structure, and reactivity of ferritin mineral core also require investigation in detail. Therefore, the stopped-flow rapid kinetics of ferroxidase activity (ΔA650/Δt) of Mtb BfrB was carried out, which detected a transient intermediate similar to diferric peroxo species as observed in frog and human ferritins. Increasing phosphate concentration increased the initial rate of iron mineralization (ΔA350/Δt) and dissolved O2 consumption (both ∼1.5-2-fold). Phosphate not only decreased the amount of iron loading and size of the BfrB mineral core (both up to 2-fold) but also decreased its crystallinity, resembling the variations observed in the core morphology of different native ferritins. In addition, phosphate inhibited the kinetics of reductive iron mobilization (∼6-8-fold) indicating its influence on the stability of the iron mineral core. Hence, the current work provides the kinetic/mechanistic insight toward the ferroxidase activity in Mtb BfrB, apart from demonstrating the role of phosphate toward the structure/reactivity of its iron mineral.

Application of crossflow ultrafiltration for scaling up the purification of a recombinant ferritin.

Ferritin proteins are taking center stage as smart nanocarriers for drug delivery due to their hollow cage-like structures and their unique 24-meric assembly. Among all ferritins, the chimeric Archaeoglobus ferritin (HumFt) is able assemble/disassemble varying the ionic strength of the medium while recognizing human TfR1 receptor overexpressed in cancer cells. In this paper we present a highly efficient, large scale purification protocol mainly based on crossflow ultrafiltration, starting from fermented bacterial paste. This procedure allows one to obtain about 2 g of purified protein starting from 100 g of fermented bacterial paste. The current procedure can easily remove contaminant proteins as well as DNA molecules in the absence of expensive and time consuming chromatographic steps.

Pea Ferritin Stability under Gastric pH Conditions Determines the Mechanism of Iron Uptake in Caco-2 Cells.

Background: Iron deficiency is an enduring global health problem that requires new remedial approaches. Iron absorption from soybean-derived ferritin, an ∼550-kDa iron storage protein, is comparable to bioavailable ferrous sulfate (FeSO4). However, the absorption of ferritin is reported to involve an endocytic mechanism, independent of divalent metal ion transporter 1 (DMT-1), the transporter for nonheme iron. Objective: Our overall aim was to examine the potential of purified ferritin from peas (Pisum sativum) as a food supplement by measuring its stability under gastric pH treatment and the mechanisms of iron uptake into Caco-2 cells. Methods: Caco-2 cells were treated with native or gastric pH-treated pea ferritin in combination with dietary modulators of nonheme iron uptake, small interfering RNA targeting DMT-1, or chemical inhibitors of endocytosis. Cellular ferritin formation, a surrogate measure of iron uptake, and internalization of pea ferritin with the use of specific antibodies were measured. The production of reactive oxygen species (ROS) in response to equimolar concentrations of native pea ferritin and FeSO4 was also compared. Results: Pea ferritin exposed to gastric pH treatment was degraded, and the released iron was transported into Caco-2 cells by DMT-1. Inhibitors of DMT-1 and nonheme iron absorption reduced iron uptake by 26-40%. Conversely, in the absence of gastric pH treatment, the iron uptake of native pea ferritin was unaffected by inhibitors of nonheme iron absorption, and the protein was observed to be internalized in Caco-2 cells. Chlorpromazine (clathrin-mediated endocytosis inhibitor) reduced the native pea ferritin content within cells by ∼30%, which confirmed that the native pea ferritin was transported into cells via a clathrin-mediated endocytic pathway. In addition, 60% less ROS production resulted from native pea ferritin in comparison to FeSO4. Conclusion: With consideration that nonheme dietary inhibitors display no effect on iron uptake and the low oxidative potential relative to FeSO4, intact pea ferritin appears to be a promising iron supplement.

The importance of antibody orientation in the electrochemical detection of ferritin.

The way of immobilization of the monoclonal antibody (type IgG) on the electrode surface has a significant effect on the amount of the immobilized protein and in consequence on current signal of protein. Herein, we demonstrate that the application of appropriately functionalized phenyl film allowed us to control the orientation of the antibody (Ab) molecules on the electrode surface. The influence of Ab orientation on the efficiency of antigen-antibody interaction was tested with an example blood plasma protein (ferritin; Ft). To control the orientation of Ab molecules the phenyl films containing -COOH or -NH2 groups were applied. Contrary to aminoethylophenyl layer, the carboxyphenyl film guaranteed the shortest distance between the redox center of the protein and the electrode surface. Additionally, the application of an external magnetic field together with magnetic nanoparticles allowed achieving the best orientation to observe well-defined ferritin current signals. The proposed method of ferritin detection can be successfully used in the concentration range of Ft between 0.1 and 30 µg dL-1. The detection limit for a carboxyphenyl film was estimated as 0.40 ±â€¯0.04 and 0.13 ±â€¯0.04 µg dL-1 for impedance and voltammetric measurements, respectively. In turn, for an aminoethylophenyl film the detection limit was 0.03 ±â€¯0.002 (electrochemical impedance spectroscopy; EIS) and 0.02 ±â€¯0.002 µg dL-1 (differential pulse voltammetry, DPV). The interday precision (reproducibility) was calculated (4.10 ÷ 9.10% RSD) together with the intraday precision / repeatability (3.20 ÷ 8.0% RSD) for the studied samples. The functionality of the sensor has been tested on rat blood samples. Based on the performed investigations it can be stated that the developed sensor was characterized by high selectivity and good sensitivity.

Ferritin from the haemolymph of adult ants: an extraction method for characterization and a ferromagnetic study.

Ferritin has been studied in many animals, plants and bacteria. The main functions of ferritin in mammals are iron concentration and stabilization, protection against oxidants and iron storage for later developmental or iron-dependent activities. Although insect ferritin plays a key role in iron transport, only a few studies to date have examined its properties and function. Ferritin isolation from the haemolymph of adult Camponotus sericeiventris ants involved heating at 75 °C, followed by protein fractionation with 3.2 M KBr gradients and ferritin sedimentation with KBr. Protein identification was performed using high-resolution proteomics techniques. SDS-PAGE revealed three subunits with molecular weights (MW) of 26, 28 and 31 kDa. Native PAGE indicated a MW higher than 669 kDa. Proteomic analysis strongly suggested the 26 and 31 kDa bands as F2LCH and F1HCH subunits of ferritin, respectively. Ferromagnetic resonance (FMR) at 100 K showed, at low field, a characteristic broad component of the ferritin iron core, suggesting that its distribution was shifted to values greater than 3000, a higher content than in mammals. The protein yield and MW were comparable to those reported in other studies of insects. To the best of our knowledge, this is the first report on ferritin extracted from adult ants to date. These results are discussed on the basis of the protein structure-function relation of secreted insect and mammal ferritins. This purification method will allow the use of magnetic techniques, which are relevant for understanding the role of ferritin in the biomineralization of magnetic nanoparticles in insects.

ironPhone: Mobile device-coupled point-of-care diagnostics for assessment of iron status by quantification of serum ferritin.

Iron deficiency (ID) is an urgent public health problem that has devastating effects on maternal and child health. However, due to poor access and affordability, screening and diagnosis for ID is often limited to proxy hemoglobin measurements alone. Here, we report the development and validation of ironPhone, a mobile-device coupled portable diagnostics for quantification of serum ferritin concentrations, an iron status biomarker, within a few minutes, from a drop of fingerprick blood. The ironPhone diagnostic platform comprises of a smartphone accessory, an app, and a disposable lateral flow immunoassay test strip to quantify serum ferritin. For initial validation in the lab, we optimized and evaluated the performance of ironPhone with known ferritin concentrations in spiked buffer and serum samples. Following lab validation, we performed a human validation by collecting fingerprick whole blood samples from 20 participants to assess iron status using ironPhone and compared the results with the laboratory standard IMMULITE 2000 analyzer. Findings from the ironPhone for the buffer and spiked serum samples provided a calibration curve with R2 values of 0.97 (n=27) and 0.93 (n=12), respectively. On comparison with the laboratory standard IMMULITE analyzer in whole blood samples, a correlation of 0.92 (P<0.0001) was observed with a sensitivity of over 90% for predicting ID (ferritin<15.0µg/L) via the ironPhone, demonstrating its promise for iron status assessment at the point-of-care.

Efficient expression of recombinant human heavy chain ferritin (FTH1) with modified peptides.

Human heavy chain ferritin (FTH1) can self-assemble into a diameter of 12-nm spherical cage with an interior cavity of 8 nm in diameter. FTH1 has great potential as a nanocage in molecular imaging and drug delivery. Different peptides have been fused with FTH1 for targeting delivery; however, the expression of FTH1 modified with peptides in soluble form is not equivalent to natural FTH1. As shown in recent study, a novel scaffold protein --thioredoxin from the archaebacterium Pyrococcus furiosus (PfTrx)--exhibits a superior solubilization capacity and thermal stability [19]. Here we report a new construct (FTH1-PfTrx-His) that can be easily expressed and purified in Escherichia coli. Of note, different peptides inserted into FTH1-PfTrx-His did not influence the expression of proteins. Finally, the doxorubicin packaging ability of FTH1-PfTrx-His is comparable to natural FTH1. Our results showed that FTH1-PfTrx-His had a potential role as a novel peptide-modified ferritin carrier for drugs or imaging probes.

Evidence that ferritin is associated with light production in the mucus of the marine worm Chaetopterus.

The blue glow of the mucus from Chaetopterus involves a photoprotein, iron and flavins. Identity and respective role of these components remain, however, largely unresolved today, likely because of viscosity issues and inhibition of this system by oxidizers conventionally used to track bioluminescence activity. Here, we used gentle centrifugation to obtain a mucus supernatant showing no inhibition to oxidizers, allowing for further analysis. We applied conventional chromatographic techniques to isolate major proteins associated with light emission. Luminescence ability of elutriate fractions was tested with hydrogen peroxide to track photoprotein and/or protein-bound chromophore. Fractions producing light contained few major proteins, one with similarity to ferritin. Addition to the mucus of elements with inhibitory/potentiary effect on ferritin ferroxidase activity induced corresponding changes in light production, emphasizing the possible role of ferritin in the worm bioluminescence. DNA of the protein was cloned, sequenced, and expressed, confirming its identity to a Chaetopterus Ferritin (ChF). Both ferric and ferrous iron were found in the mucus, indicating the occurrence of both oxidase and reductase activity. Biochemical analysis showed ChF has strong ferroxidase activity, which could be a source of biological iron and catalytic energy for the worm bioluminescence when coupled to a reduction process with flavins.

Molecular cloning, overexpression, purification, and sequence analysis of the giant panda (Ailuropoda melanoleuca) ferritin light polypeptide.

The complementary DNA (cDNA) of the giant panda (Ailuropoda melanoleuca) ferritin light polypeptide (FTL) gene was successfully cloned using reverse transcription-polymerase chain reaction technology. We constructed a recombinant expression vector containing FTL cDNA and overexpressed it in Escherichia coli using pET28a plasmids. The expressed protein was then purified by nickel chelate affinity chromatography. The cloned cDNA fragment was 580 bp long and contained an open reading frame of 525 bp. The deduced protein sequence was composed of 175 amino acids and had an estimated molecular weight of 19.90 kDa, with an isoelectric point of 5.53. Topology prediction revealed one N-glycosylation site, two casein kinase II phosphorylation sites, one N-myristoylation site, two protein kinase C phosphorylation sites, and one cell attachment sequence. Alignment indicated that the nucleotide and deduced amino acid sequences are highly conserved across several mammals, including Homo sapiens, Cavia porcellus, Equus caballus, and Felis catus, among others. The FTL gene was readily expressed in E. coli, which gave rise to the accumulation of a polypeptide of the expected size (25.50 kDa, including an N-terminal polyhistidine tag).

M. tuberculosis ferritin (Rv3841): Potential involvement in Amikacin (AK) & Kanamycin (KM) resistance.

Tuberculosis is an infectious disease, caused by one of the most successful human pathogen, Mycobacterium tuberculosis. Aminoglycosides, Amikacin (AK) & Kanamycin (KM) are commonly used to treat drug resistant tuberculosis. They target the protein synthesis machinery by interacting with several steps of translation. Several explanations have been proposed to explain the mechanism of aminoglycoside resistance but still our information is inadequate. Iron storing/interacting proteins were found to be overexpressed in aminoglycosides resistant isolates. Iron assimilation and utilization in M. tuberculosis plays a crucial role in growth, virulence and latency. To establish the relationship of ferritin with AK & KM resistance ferritin (Rv3841/bfrB) was cloned, expressed and antimicrobial drug susceptibility testing (DST) was carried out. Rv3841/bfrB gene was cloned and expressed in E. coli BL21 using pQE2 expression vector. Etest results for DST against AK & KM showed that the minimum inhibitory concentration (MIC) of ferritin recombinant cells was changed. Recombinants showed two fold changes in MIC with AK and three fold with KM E-strips. Overexpression of ferritin reflect the MIC shift which might be playing a critical role in the survival of mycobacteria by inhibiting/modulating the effects of AK & KM. String analysis also suggests that ferritin interacted with few proteins which are directly and indirectly involved in M. tuberculosis growth, Iron assimilation, virulence, resistance, stresses and latency.

An evaluation of ELISA using recombinant Brucella abortus bacterioferritin (Bfr) for bovine brucellosis.

To date, detection of antibodies against the lipopolysaccharide portion is the backbone of most serodiagnostic methods for brucellosis screening. However this pose a risk for false positive reactions related to other pathogens especially that of Yersinia enterocolitica O:9 which has the most prominent cross reactivity with Brucella spp. In this study, cloning and expression of Brucella abortus bacterioferritin (Bfr) was accomplished by PCR amplification into an expression vector system, and purification of a recombinant B. abortus Bfr (rBfr). The immunogenicity of rBfr was confirmed by Western blot with Brucella-positive bovine serum. To determine whether rBfr has a potential benefit for use in the serodiagnosis of bovine brucellosis, rBfr-based ELISA was performed. Interestingly, rBfr was able to detect anti-Brucella antibodies in positive sera in a dependent manner of TAT values but did not show an immunoreaction with negative samples. Particularly, average OD492 values at the lowest, medium and highest TAT titer levels were 1.4, 2.2 and 2.6-fold increase compared with the cutoff value, respectively. The accuracy, specificity and sensitivity of rBfr showed 89.09%, 93.6% and 85.33%, respectively. These findings suggest that rBfr might be a good candidate for serological diagnosis development of bovine brucellosis.

Enrichment and characterization of ferritin for nanomaterial applications.

Ferritin is a ubiquitous iron storage protein utilized as a nanomaterial for labeling biomolecules and nanoparticle construction. Commercially available preparations of horse spleen ferritin, widely used as a starting material, contain a distribution of ferritins with different iron loads. We describe a detailed approach to the enrichment of differentially loaded ferritin molecules by common biophysical techniques such as size exclusion chromatography and preparative ultracentrifugation, and characterize these preparations by dynamic light scattering, and analytical ultracentrifugation. We demonstrate a combination of methods to standardize an approach for determining the chemical load of nearly any particle, including nanoparticles and metal colloids. Purification and characterization of iron content in monodisperse ferritin species is particularly critical for several applications in nanomaterial science.

A ferritin-like protein with antioxidant activity in Ureaplasma urealyticum.

BACKGROUND: Ureaplasma urealyticum is a major pathogen associated with many diseases. The ability of U. urealyticum to protect itself from oxidative stress is likely to be important for its pathogenesis and survival, but its oxidative stress tolerance mechanisms remain unclear. This study investigates the antioxidant activity of a ferritin-like protein from U. urealyticum. RESULTS: The uuferritin gene, which was up regulated when U. urealyticum was subjected to oxidative stress, was cloned from U. urealyticum and the corresponding recombinant protein uuferritin was purified. Uuferritin protein reduced the levels of hydroxyl radicals generated by the Fenton reaction as a consequence of its ferroxidase activity, and thus the protein protected DNA from oxidative damage. Furthermore, oxidation-sensitive Escherichia coli mutants transformed with pTrc99a-uuferritin showed significantly improved tolerance to oxidative stress compared to E. coli mutants transformed with an empty pTrc99a vector. CONCLUSIONS: The present work shows that uuferritin protein confers resistance to oxidative stress in vitro and in E. coli. The protective role of uuferritin provides a foundation for understanding the mechanisms of oxidative stress tolerance in U. urealyticum.

Towards instantaneous cellular level bio diagnosis: laser extraction and imaging of biological entities with conserved integrity and activity.

The prospect for spatial imaging with mass spectroscopy at the level of the cell requires new means of cell extraction to conserve molecular structure. To this aim, we demonstrate a new laser extraction process capable of extracting intact biological entities with conserved biological function. The method is based on the recently developed picosecond infrared laser (PIRL), designed specifically to provide matrix-free extraction by selectively exciting the water vibrational modes under the condition of ultrafast desorption by impulsive vibrational excitation (DIVE). The basic concept is to extract the constituent protein structures on the fastest impulsive limit for ablation to avoid excessive thermal heating of the proteins and to use strongly resonant 1-photon conditions to avoid multiphoton ionization and degradation of the sample integrity. With various microscope imaging and biochemical analysis methods, nanoscale single protein molecules, viruses, and cells in the ablation plume are found to be morphologically and functionally identical with their corresponding controls. This method provides a new means to resolve chemical activity within cells and is amenable to subcellular imaging with near-field approaches. The most important finding is the conserved nature of the extracted biological material within the laser ablation plume, which is fully consistent with in vivo structures and characteristics.

Ferritin encapsulation and templated synthesis of inorganic nanoparticles.

Understanding how inorganic nanoparticles interact with proteins is paramount to their safe and effective use in vivo. Ordered protein-inorganic nanomaterial assemblies will also enable the creation of patterned structures with useful physical properties. Thermophilic ferritin (tF) from Archaeoglobus fulgidus has unique structural features and self-assembly properties that facilitate stable but also reversible interaction with gold nanoparticles (AuNPs). In this chapter we describe how to express and purify tF and induce its assembly around AuNPs. We also describe methods for characterizing the tF-AuNP complex as well as templating NP growth within the protein cavity.

Differential scanning calorimetry to quantify the stability of protein cages.

Differential scanning calorimetry (DSC) is an experimental technique through which the differences in amount of heat required to maintain equal temperature between a sample and a reference cell are measured at various temperatures. The quantified heat relates to the differences in apparent heat capacity of the analytes. The data from DSC studies will thereby provide direct information about the energetics of thermally induced processes in the sample. Here we present a detailed protocol to quantify the thermostability of protein cage, bacterioferritin (BFR), using differential scanning calorimetry.

The usage of phage mini-antibodies as a means of detecting ferritin concentration in animal blood serum.

Mini-antibodies that have specific ferritin response have been produced for the first time using sheep's phage libraries (Griffin.1, Medical Research Council, Cambridge, UK). Produced phage antibodies were used for the first time for the development of diagnostic test kits for ferritin detection in the blood of cattle. The immunodot assay with secondary biospecific labeling is suggested as means of ferritin detection in cow blood serum (antiferritin phage antibodies and rabbit antiphage antibodies conjugated with different labels). Сolloidal gold, gold nanoshells, and horse reddish peroxidase used as labels have shown a similar response while detecting concentration of ferritin (0.2 mg/mL). It is shown that the method of solid-phase immunoassay with a visual view of the results allows determination of the minimum concentration of ferritin in the blood of cows at 0.225 g/mL.