Diversity of DNA-hydrolyzing antibodies from the sera of autoimmune-prone MRL/MpJ-lpr mice

It has been shown for the first time that polyclonal IgG abzymes (Abzs) with DNase activity from the sera of autoimmune-prone MRL/MpJ-lpr mice can be separated by isoelectric focusing into many subfractions having the isoelectric points (pI) from 4.5 to 9, with the maximal activity for Abzs with pI = 6.5-9.0. Affinity chromatography on DNA-cellulose separated DNase IgGs into many subfractions demonstrating a range of affinities for DNA and different levels of the relative DNase activities (RDA) due to intrinsically bound metals and after addition of external Mg(2+) , Mn(2+) , Ca(2+), and Mg(2+) +Ca(2+). Some fractions significantly increase RDAs in the presence of external ions (Mg(2+) + Ca(2+)  > Mg(2+)  > Mn(2+)  > Ca(2+)), while each of this cofactor can also inhibit or have no influence on the RDAs of another fractions. It is known that complexes of DNA with histones and other proteins of apoptotic cells are the primary immunogens in systemic lupus erythematosus (SLE). Bovine serum albumin (BSA) and methylated BSA (mBSA) increase the RDAs of only some fractions, while have no effect or inhibit other IgG fractions. The ratio of the RDAs in the presence of all metal ions, BSA, and mBSA was individual for every abzyme fraction. Mn(2+) and Ca(2+) stimulated accumulation of only relaxed form of supercoiled DNA (scDNA) in the case of all subfractions, while in the presence of Mg(2+) antibodies (Abs) of some subfractions (and in the presence of Mn(2+) +Ca(2+) all subfractions) produced relaxed DNA (rDNA) and linear DNA (linDNA) in a variable extent. The data obtained show that the polyclonal Abzs of mice may be a cocktail of Abs directly to DNA, RNA, and their complexes with proteins and anti-idiotypic Abs to active centers of different nucleases. The diversity of the physicochemical and kinetic characteristics of the Abzs seems to be significantly widened when pre-diseased mice spontaneously develop the disease.

Natural catalytic antibodies in norm, autoimmune, viral, and bacterial diseases

In human patients with autoimmune, viral, and bacterial diseases, the generation of antibodies (Abs) to foreign antigens and/or autoantibodies to self-antigens usually occurs. Some Abs with different catalytic activities (abzymes, Abzs) may be induced spontaneously by primary antigens and can have characteristics of the primary antigen, including the catalytic activity of idiotypic and/or anti-idiotypic Abs. Healthy humans usually do not develop Abzs or their activities are low, often on the borderline of sensitivity of the detection methods. Detection of Abzs was shown to be the earliest indicator of development of different autoimmune diseases (ADs). At the early stages of ADs, the repertoire of Abzs is usually relatively narrow, but it greatly expands with the progress of the disease, leading to the generation of catalytically diverse Abzs with different activities and functions. Some Abzs are cytotoxic and can play an important negative role in the pathogenesis of ADs, while positive roles have been proposed for other Abzs. Abzs with some low activities can temporarily be present in the blood of patients in the course of viral and bacterial diseases, but their activity increases significantly if these infections stimulate development of ADs. A significant increase in the relative Abz activities associated with a specific reorganization of the immune system, including changes in the differentiation and proliferation of bone marrow hematopoietic stem cells and lymphocyte proliferation in different organs. Different mechanisms of Abz production can be proposed for healthy externally immunized and for autoimmune mammals during the development of pathology.

Peculiarities of abzymes from sera and milk of healthy donors and patients with autoimmune and viral diseases

The detection of catalytic activity of antibodies is the earliest indicator of development of autoimmune diseases (AID). In early stages of AID, the repertoire of abzymes with various properties is relatively small, but it is greatly increased during their development. Catalytic diversity of the abzymes includes DNase, RNase, ATPase, and oxidoreductase activities; there are antibodies phosphorylating proteins, lipids, and polysaccharides. This review summarizes new data on abzyme heterogeneity and possible reasons for this phenomenon. A possible role of abzymes and their exceptional multiplicity in the pathogenesis of different AID is discussed.

DNA-hydrolyzing activity of IgG antibodies from the sera of patients with tick-borne encephalitis

DNase autoantibodies (Abzs) can be found in the blood of patients with several autoimmune diseases, while the blood of healthy donors or patients with diseases with an insignificant disturbance of the immune status does not contain DNase Abzs. Here we present the first analysis of the DNase Abzs activity in the patients with tick-borne encephalitis (TBE). Several strict criteria have been applied to show that the DNase activity is an intrinsic property of IgGs from the sera of TBE patients but not from healthy donors. The relative activity of IgGs has been shown to vary extensively from patient to patient, but most of the preparations (91%) had detectable levels of the DNase activity. Polyclonal DNase IgGs were not active in the presence of EDTA or after a dialysis against EDTA, but could be activated by several externally added metal ions, with the level of activity decreasing in the order Mn(2+) + Ca(2+) > or = Mn(2+)+ Mg(2+) > or = Mn(2+) > or = Mg(2+) + Ca(2+) > or = Co(2+) > or = Mg(2+) > Ca(2+), while K(+), Na(+), Ni(2+), Zn(2+), and Cu(2+) did not stimulate DNA hydrolysis. Affinity chromatography on DNA-cellulose separated the DNase IgGs into many subfractions with various affinities for DNA and very different levels of the relative activity. Possible reasons for catalytic diversity of polyclonal human Abzs are discussed.

DNA, oligosaccharides, and mononucleotides stimulate oligomerization of human lactoferrin

Using small-angle X-ray scattering (SAXS), light scattering (LS), and soft laser ablation we have shown that lactoferrin (LF) in solution at neutral pH is oligomerized in the absence of salt or at physiological salt concentrations. The level of oligomerization depends on the concentration of LF, KCl or NaCl, and on the duration of the protein storage in solution. At the concentrations comparable with those in human milk (1-6 mg/ml), the average radius of gyration (R(g)) values of LF can attain 400-480 A, while fresh solution of previously lyophylized LF demonstrate a lower average R(g) (50-100 A), and R(g) value characterizing the LF monomer formed at 1 M NaCl is 26.7 A. The addition of oligonucleotides, oligosaccharides, or mononucleotides to LF in the presence or in the absence of KCl with different level of initial oligomerization accelerates the oligomerization rate and increases the R(g) values up to approximately 600-700 A, which correspond to associates containing ten or more protein molecules. During gel filtration on Sepharose 4B, high-degree LF oligomers dissociate nearly completely forming different degraded complexes, but in some cases it is possible to reveal small amount of a decamer. A possible role for oligomerization of LF, a highly polyfunctional protein, for its different biological activities is discussed.

DNA-hydrolysing activity of IgG antibodies from the sera of patients with diseases caused by different bacterial infections

DNase autoantibodies (Abs) can be found in the blood of patients with several autoimmune diseases, while the blood of healthy donors or patients with diseases with insignificant disturbances of the immune status does not contain the DNase Abs. Here we have analysed for the first time the DNase activity in the patients with diseases caused by several bacterial infections. Several rigid criteria have been applied to show that the DNase activity is an intrinsic property of IgGs from the sera of patients with bacterial diseases but not from healthy donors. The relative activity of IgGs has been shown to vary extensively between the diseases analysed and from patient to patient, but most of the preparations had detectable levels of the DNase activity. On average, the catalytic activities were significantly lower than in patients with autoimmune pathologies and increased in the following order: streptococcal infection (erysipelas) < urogenital chlamydiosis associated with arthritis (Reiter's disease) < meningococcal meningitis < shigellosis < suppurative surgical infections caused by Staphylococcus aureus < suppurative surgical infections caused by epidermal staphylococci < urogenital ureaplasmosis associated with reactive arthritis. While intact IgGs possessed this catalytic activity, separated light chains of polyclonal Abs appeared to be even more active in the hydrolysis of DNA.

Nucleotide-hydrolyzing antibodies from the sera of autoimmune-prone MRL-lpr/lpr mice

Abzymes (Abzs) with different enzymic activities have been detected in the sera of patients with various autoimmune (AI) diseases and in AI mice. In this work, electrophoretically homogeneous IgGs were isolated from the sera of MRL-lpr/lpr mice spontaneously developing lupus-like AI pathology. It was shown for the first time that polyclonal IgGs (pIgGs) and their isolated heavy and light chains hydrolyze different nucleoside-5'-triphosphate (NTPs), nucleoside-5'-diphosphate (NDPs), adenosine monophosphate and deoxiadenosine-5'-monophosphate (dAMP), whereas antibodies from the sera of control healthy mice were catalytically inactive. Monoclonal mouse IgGs also effectively hydrolyze nucleotides. The data demonstrate that nucleotide-hydrolyzing activity is an intrinsic property of isolated mouse pIgG and monoclonal IgG. It was shown that various markers of AI pathologies (proteinuria and antibody titers to native and denatured DNA) demonstrating spontaneous development of AI reactions increased in animals with aging and correlated with an increase in Abz relative activity in hydrolysis of nucleotides. The highest increase in AI reaction markers and in Abz enzymic activity was found in mice immunized with a DNA-protein complex.

Oxidoreductase activities of polyclonal IgGs from the sera of Wistar rats are better activated by combinations of different metal ions

It was shown that IgGs purified from the sera of healthy Wistar rats contain several different bound Me2+ ions and oxidize 3,3'-diaminobenzidine through a H2O2-dependent peroxidase and H2O2-independent oxidoreductase activity. IgGs have lost these activities after removing the internal metal ions by dialysis against EDTA. External Cu2+ or Fe2+ activated significantly both activities of non-dialysed IgGs containing different internal metals (Fe > or = Pb > or = Zn > or = Cu > or = Al > or = Ca > or = Ni > or = Mn > Co > or = Mg) showing pronounced biphasic dependencies corresponding to approximately 0.1-2 and approximately 2-5 mM of Me2+, while the curves for Mn2+ were nearly linear. Cu2+ alone significantly stimulated both the peroxidase and oxidoreductase activities of dialysed IgGs only at high concentration (> or = 2 mM), while Mn2+ weakly activated peroxidase activity at concentration >3 mM but was active in the oxidoreductase oxidation at a low concentration (<1 mM). Fe2+-dependent peroxidase activity of dialysed IgGs was observed at 0.1-5 mM, but Fe2+ was completely inactive in the oxidoreductase reaction. Mg2+, Ca2+, Zn2+, Al2+ and especially Co2+ and Ni2+ were not able to activate dialysed IgGs, but slightly activated non-dialysed IgGs. The use of the combinations of Cu2+ + Mn2+, Cu2+ + Zn2+, Fe2+ + Mn2+, Fe2+ + Zn2+ led to a conversion of the biphasic curves to hyperbolic ones and in parallel to a significant increase in the activity as compared with Cu2+, Fe2+ or Mn2+ ions taken separately; the rates of the oxidation reactions, catalysed by non-dialysed and dialysed IgGs, became comparable. Mg2+, Co2+ and Ni2+ markedly activated the Cu2+-dependent oxidation reactions catalysed by dialysed IgGs, while Ca2+ inhibited these reactions. A possible role of the second metal in the oxidation reactions is discussed.

Affinity and catalytic heterogeneity of polyclonal myelin basic protein-hydrolyzing IgGs from sera of patients with multiple sclerosis

Human myelin basic protein (hMBP)-hydrolyzing activity was recently shown to be an intrinsic property of antibodies (Abs) from multiple sclerosis (MS) patients. Here, we present the first evidence demonstrating a significant diversity of different fractions of polyclonal IgGs (pIgGs) from MS patients in their affinity for hMBP and in the ability of pIgGs to hydrolyze hBMP at different optimal pHs (3–10.5). IgGs containing λ- and κ-types of light chains demonstrated comparable relative activities in the hydrolysis of hMBP. IgGs of IgG1–IgG4 sub-classes were analyzed for catalytic activity. IgGs of all four sub-classes were catalytically active, with their contribution to the total activity of Abzs in the hydrolysis of hMBP and its 19-mer oligopeptide increasing in the order: IgG1 (1.5–2.1%) < IgG2 (4.9–12.8%) < IgG3 (14.7–25.0%) < IgG4 (71–78%). Our findings suggest that the immune systems of individual MS patients generate a variety of anti-hMBP abzymes with different catalytic properties, which can attack hMBP of myelin-proteolipid shell of axons, playing an important role in MS pathogenesis.

Antibodies against DNA hydrolyze DNA and RNA

In this work, rabbits were immunized with a high polymer DNA complexed with methylated BSA (mBSA) and by mBSA. It is shown that electrophoretically homogeneous preparations of polyclonal antibodies (Ab) from non-immunized rabbits and animals immunized by mBSA do not exhibit catalytic activity. Ab from the blood of rabbits immunized with the DNA-mBSA complex hydrolyzed poly(C) and different RNAs with efficiency exceeding that towards DNA by approximately 3-4 orders of magnitude. Affinity chromatography of the IgG on DNA cellulose separated the Ab into fractions hydrolyzing both RNA and DNA, and for the first time fractions that hydrolyze only RNA were found. Kinetic parameters that characterize the RNA and DNA hydrolysis by initial Ab preparations and their fractions obtained by separation on an affinity sorbent are compared.

[DNA and oligosaccharides stimulate oligomerization of human milk lactoferrin]

Lactoferrin (LF), the glycoprotein transferring Fe+ ions, is contained in barrier liquids, human blood and milk. LF is an acute phase protein and one of the most important factors of nonspecific defense. The protein has unique set of biological functions. Using the methods of small-angle X-ray scattering and light-scattering it was shown for the first time that addition of DNA and oligosaccharides to LF with different level of initial oligomerization leads to an enhance in the oligomerization rate. 1M NaCl stimulates almost a complete dissociation of LF oligomeric complexes obtained in the pesence of DNA, oligosaccharides, or early founded oligomerization effectors (nucleotides). It was shown that LF oligomeric complexes obtained in the presence of different oligomerization effectors have different stability. Incubation with 50 mM MgCl2 leads to complete destruction of the protein complexes formed by ATP and oligosaccharide but partially dissociate the complexes with following formation of new in the case of AMP- and d(pT)10-dependent associates, which possess higher stability i n presence of the salt. A possible role of LF oligomerization for different biological functions of the protein is discussed.

Antibodies against RNA hydrolyze RNA and DNA

Immunization of animals with DNA leads to the production of anti-DNA antibodies (Abs) demonstrating both DNase and RNase activities. It is currently not known whether anti-RNA Abs can possess nuclease activities. In an attempt to address this question, we have shown that immunization of three rabbits with complex of RNA with methylated BSA (mBSA) stimulates production of IgGs with RNase and DNase activities belonging to IgGs, while polyclonal Abs from three non-immunized rabbits and three animals immunized with mBSA are catalytically inactive. Affinity chromatography of IgGs from the sera of autoimmune (AI) patients on DNA-cellulose usually demonstrates a number of fractions, all of which effectively hydrolyze both DNA and RNA, while rabbit catalytic IgGs were separated into Ab subfractions, some of which demonstrated only DNase activity, while others hydrolyzed RNA faster than DNA. The enzymic properties of the RNase and DNase IgGs from rabbits immunized with RNA distinguish them from all known canonical RNases and DNases and DNA- and RNA-hydrolyzing abzymes (Abzs) from patients with different AI diseases. In contrast to RNases and AI RNA-hydrolyzing Abs, rabbit RNase IgGs catalyze only the first step of the hydrolysis reaction but cannot hydrolyze the formed terminal 2',3'-cyclophosphate. The data indicate that Abzs of AI patients hydrolyzing nucleic acids in part may be Abs against RNA and its complexes with proteins.

Immunization of rabbits with DNase I produces polyclonal antibodies with DNase and RNase activities

Immunization of rabbits with DNase I leads to the production of antiidiotypic Abs with DNase activity. It is not known at present whether antiidiotypic Abs against DNA-hydrolyzing enzymes can possess RNase activity. Here we show that immunization of healthy rabbits with bovine DNase I produces IgGs with intrinsic DNase and RNase activities. Electrophoretically and immunologically homogeneous polyclonal IgGs were obtained by sequential chromatography of the immune sera on Protein A-Sepharose and gel filtration. Affinity chromatography on DNA cellulose using elution of Abs with different concentrations of NaCl and an acidic buffer separated catalytic IgGs into four Ab subfractions, three of which demonstrated only DNase activity while one subfraction hydrolyzed RNA faster than DNA. The serum of patients with many different autoimmune (AI) diseases contains small fractions of antibodies (Abs) interacting with immobilized DNA, which possess both DNase and RNase activities. Our data suggest that a fraction of abzymes from AI patients hydrolyzing both DNA and RNA can contain a subfraction of Abs against DNase I.

Activation of DNA-hydrolyzing antibodies from the sera of autoimmune-prone MRL-lpr/lpr mice by different metal ions

We have shown previously that electrophoretically and immunologically homogeneous polyclonal IgGs from the sera of autoimmune-prone MRL mice possess DNase activity. Here we have analyzed for the first time activation of DNase antibodies (Abs) by different metal ions. Polyclonal DNase IgGs were not active in the presence of EDTA or after Abs dialysis against EDTA, but could be activated by several externally added metal (Me(2+)) ions, with the level of activity decreasing in the order Mn(2+)> or =Mg(2+)>Ca(2+)> or =Cu(2+)>Co(2+)> or =Ni(2+)> or =Zn(2+), whereas Fe(2+) did not stimulate hydrolysis of supercoiled plasmid DNA (scDNA) by the Abs. The dependencies of the initial rate on the concentration of different Me(2+) ions were generally bell-shaped, demonstrating one to four maxima at different concentrations of Me(2+) ions in the 0.1-12 mM range, depending on the particular metal ion. In the presence of all Me(2+) ions, IgGs pre-dialyzed against EDTA produced only the relaxed form of scDNA and then sequence-independent hydrolysis of relaxed DNA followed. Addition of Cu(2+), Zn(2+), or Ca(2+) inhibited the Mg(2+)-dependent hydrolysis of scDNA, while Ni(2+), Co(2+), and Mn(2+) activated this reaction. The Mn(2+)-dependent hydrolysis of scDNA was activated by Ca(2+), Ni(2+), Co(2+), and Mg(2+) ions but was inhibited by Cu(2+) and Zn(2+). After addition of the second metal ion, only in the case of Mg(2+) and Ca(2+) or Mn(2+) ions an accumulation of linear DNA (single strand breaks closely spaced in the opposite strands of DNA) was observed. Affinity chromatography on DNA-cellulose separated DNase IgGs into many subfractions with various affinities to DNA and very different levels of the relative activity (0-100%) in the presence of Mn(2+), Ca(2+), and Mg(2+) ions. In contrast to all human DNases having a single pH optimum, mouse DNase IgGs demonstrated several pronounced pH optima between 4.5 and 9.5 and these dependencies were different in the presence of Mn(2+), Ca(2+), and Mg(2+) ions. These findings demonstrate a diversity of the ability of IgG to function at different pH and to be activated by different optimal metal cofactors. Possible reasons for the diversity of polyclonal mouse abzymes are discussed.

Polysaccharide kinase activity of human milk IgG antibodies

A small fraction of human milk IgG antibodies is shown to possess polysaccharide kinase activity for the first time. Unlike all known kinases, IgG antibodies can use as phosphate donor not only [gamma-(32)P]ATP, but also directly [(32)P]ortho-phosphate. Human milk IgGs therefore possess high affinity to ortho-phosphate (K(m) = 9-71 microM), which is a more effective substrate than ATP. IgG antibodies possessing polysaccharide kinase activity are yet another example of natural abzymes possessing not hydrolytic, but synthetic enzymatic activity.

Substrate specificity of rat sera IgG antibodies with peroxidase and oxidoreductase activities

We have recently shown that intact IgGs from the sera of healthy Wistar rats oxidize 3,3'-diaminobenzidine (DAB) in the presence and in the absence of H(2)O(2) similar to horseradish peroxidase (HRP). Here we demonstrate for the first time that the peroxidase and oxidoreductase activities of IgGs can efficiently oxidize not only DAB but also o-phenylendiamine, phenol, p-dihydroquinone, alpha-naphthol, and NADH but, in contrast to HRP, cannot oxidize adrenalin. In contrast to IgGs, HRP cannot oxidize phenol, p-dihydroquinone, or alpha-naphthol in the absence of H(2)O(2). In contrast to plant and mammalian peroxidases, IgGs were more universal in their metal dependence. The specific wide repertoire of polyclonal peroxidase and oxidoreductase IgGs oxidizing various substances could play an important role in protecting the organism from oxidative stress and serve as an additional natural system destroying different toxic, carcinogenic, and mutagenic compounds.

[Interactions of pro- and eukaryotic DNA repair enzymes with oligodeoxyribonucleotides containing clustered lesions]

Interactions of oxoGuanine-DNA glycosylases from Escherichia coli (Fpg) and human (OGG1) and abasic site endonucleases from yeast (Apnl) and E. coli (Nfo) with oligodeoxyribonucleotides containing oxoGuanine (oxoG) and tetrahydrofuran (F, a stable analog of an abasic site) separated by various numbers of nucleotides have been studied. Inhibitor analysis has shown that the affinity of Fpg for single-stranded ligands does not depend on the relative positions of oxoG and F lesions. KM and kcat values have been determined for all double-stranded substrates and all enzymes under study. The effect of introducing the second lesion was strongly dependent on the relative positions of the lesions and the nature of the enzyme. The highest drop in the affinity (1.6-148-fold) and the reaction rate (4.8-58-fold) has been observed with Fpg and OGG1 for substrates containing F immediately 5' or 3' adjacent to oxoG. Introduction of the second lesion barely changed the KM values for Apnl and Nfo substrates. At the same time, the reaction rates were 5-10-fold lower for substrates containing two adjacent lesions. For all enzymes studied, increasing the distance between two lesions in duplex DNA reduced the effect of the lesion in KM and kcat values.

[Interactions of human 8-oxoguanine-DNA glycosylase with single- and double-stranded DNA]

Interactions of human 8-oxoguanine-DNA glycosylase (hOGG1) with single- and double-stranded oligodeoxyribonucleotides (ODN) have been studied by the method of stepwise increase in ligand complexity. The ODNs have been found to inhibit the glycosylase-catalyzed reaction competitively. The K1 values have been determined for a set of ODNs. All units of non-specific DNA within the enzyme footprint have been shown to interact with the protein globule in an additive manner. An increase in the d(pN)n length (n) by one unit caused a monotonous 1.4-1.5-fold increase in their affinity for the glycosylase ODN until n = 10, mostly due to weak nonspecific contacts of the enzyme and the sugar-phosphate backbone. The weak nonspecific additive interactions contributed about five orders of magnitude in the affinity of hOGG1 for specific DNA (Kd approximately 10(-5) M), whereas introduction of a 8-oxoguanine residue added about three orders of magnitude to this affinity (Kd approximately 10(-8) M). Quantitative features of recognition of specific DNA by the enzyme are analyzed.

[DNA-hydrolyzing IgG antibodies from the blood of patients with acquired immune deficiency syndrome]

DNAase activity of 110 samples of IgG from the blood of AIDS patients was analyzed. It was shown that the relative activity of preparations varies very much from patient to patient, but 96% preparations show detectable level of DNAase activity. Several rigid criteria were applied and it was shown that DNAase activity is an intrinsic property of antibodies from AIDS patients. It was shown that catalytic activity could posses not only intact IgG, but also separated light chains of polyclonal antibodies. The abzymes catalyze DNA hydrolysis effectively in a wild range of pH (5.0-9.5). K(M) and V(MaKC) values of antibody-dependent hydrolysis of DNA was estimated.

Antibodies with amylase activity from the sera of autoimmune-prone MRL/MpJ-lpr mice

Animals spontaneously developing lupus-like autoimmune pathology (SLE) are very promising models to study the mechanisms of natural abzymes (Abzs) generation and their role in etiology and pathogenesis of autoimmune diseases, but Abzs from the sera of animals remain virtually unstudied. In this work, electrophoretically homogeneous IgGs were isolated from the sera of MRL/MpJ-lpr mice. It was shown for the first time that amylase activity is an intrinsic property of antibodies (Abs) and their isolated heavy and light chains. Various markers of SLE pathology (proteinuria, enhanced concentration of anti-DNA Abs) increased with spontaneous development of SLE and especially after animal immunization, correlating with the increase in Abz relative amylase activity. The highest amylase activity was found in the sera Abs of healthy mice after delivery and at the beginning of lactation; this was not correlated with markers of mouse SLE but supports the idea that pregnancy could "activate" or "trigger" autoimmune-like manifestations and Abzs production in healthy mammals. The possible differences in mechanisms of Abzs production in lactating mice and animals developing SLE are discussed.

Metal ions-dependent peroxidase and oxidoreductase activities of polyclonal IgGs from the sera of Wistar rats

We present evidence showing that a small fraction of electrophoretically homogeneous IgGs from the sera of healthy Wistar rats is bound with several different Me2+ ions and oxidizes 3,3'-diaminobenzidine through a peroxidase activity in the presence of H2O2 and through an oxidoreductase activity in the absence of H2O2. During purification on Protein A-Sepharose and gel filtration, the polyclonal IgGs partially lose the Me2+ ions. Therefore, in the absence of external metal ions, the specific peroxidase activity of IgGs from the sera of different rats varied in the range 1.6-26% and increased up to 13-198% after addition of Fe2+ or Cu2+ ions as compared with horseradish peroxidase (HRP, taken for 100%). The oxidoreductase activity of HRP is 24-fold lower than its peroxidase activity, while oxidoreductase and peroxidase activities of IgGs are comparable. Oxidoreductase activities of different IgGs in the absence of external metal ions varied from 22 to 800%, and in the presence of Fe2+ or Cu2+ ions, from 37 to 1100% in comparison with the HRP oxidoreductase activity (100%). Chromatography of the IgGs on Chelex-100 leads to the adsorption of a small IgG fraction bound with metal ions and to its separation to many different subfractions demonstrating various affinities to the chelating resin and increased levels of the specific oxidoreductase and peroxidase activities. Antioxidant enzymes such as superoxide dismutases, catalases, and glutathione peroxidases are known to represent critical defense mechanisms for preventing oxidative modifications of DNA, proteins, and lipids. Peroxidase and oxidoreductase activity of antibodies may play an important role in the protection of organisms from oxidative stress and toxic compounds.

Proteolytic activity of IgG antibodies from blood of acquired immunodeficiency syndrome patients

Proteolytic activity of polyclonal IgG antibodies (Abs) from the blood of AIDS patients was analyzed for the first time. These Abs were shown to display higher activity in hydrolysis of beta-casein than in hydrolysis of human immunodeficiency virus (HIV)-1 reverse transcriptase (RT) or human serum albumin (HSA). Several abzymatic criteria were applied and it was shown that RT, HSA, and beta-casein hydrolyzing activities are an intrinsic property of polyclonal Abs from AIDS patients. Casein-hydrolyzing Abs were detected in the blood serum for 95% of AIDS patients, and it was shown that they possess serine protease-like catalytic activity. The substrate specificities of polyclonal Ab proteases and typical human proteases are different. Depending on the patient, the IgGs exhibit various pH optima of proteolytic activity. The products of casein hydrolysis by Ab proteases were different from those in the case of trypsin, chymotrypsin, and proteinase K.

Human milk antibodies with polysaccharide kinase activity

It was shown for the first time that a small fraction of milk secretory IgA (sIgA) is tightly bound to oligosaccharides (oligoSACs) and polysaccharides (polySACs). The ability of sIgA to phosphorylate oligo- and polysaccharides was shown to be an intrinsic property of this antibody. In contrast to known kinases, sIgAs with polysaccharide kinase activity can transfer phosphoryl group to oligo- and polysaccharides not only from [gamma-(32)P]ATP but can also use [(32)P]orthophosphate as a substrate of phosphorylation reaction. An extremely unusual property of polysaccharide kinase Abs is their high affinity for orthophosphate (K(m) = 15-77 microM), and orthophosphate is a better substrate than ATP. Two first examples of natural abzymes (Abzs) with synthetic activity were milk sIgA with protein and lipid kinase activities. Polysaccharide kinase sIgA of human milk is the third example of natural antibodies (Abs) with synthetic activity.

[The effect of nucleotides on oligomeric state of human lactoferrin]

A polyfunctional protein lactoferrin (LF) which is present in human barrier fluids, blood and milk and this protein of acute phase is responsible for nonspecific cells defense against microbial and viral infection and cancer diseases. Using the methods of small-angle X-ray scattering and light-scattering it was shown that LF in solution exists in oligomeric state. The level of LF oligomerization depends upon its concentration and time of keeping of no frozen neutral protein solutions. At the concentrations comparable with those in human milk (1-6 mg/ml) the average inertial radius values (Rg) of LF can reach 100-450 angstroms, while Rg for monomer LF form is 26.7 angstroms. LF was shown to complex with different nucleotides and hydrolyze them. The addition of ATP and AMP to LF demonstrating any level of oligomerization leads to increase of oligomerization processes and enhancement of the Rg values up to 600-700 angstroms According to different models of LF monomer association to its oligomeric forms (sphere, plate, cylinder) the oligomeric complexes demonstrate high Rg values which can contain from several tens up to several thousands of LF monomers. A possible role of LF oligomerization for different biological functions of the protein is discussed.