Zinc sequestration by earthworm (Annelida: Oligochaeta) chloragocytes

Summary The elemental compositions of chloragosome granules in the earthworm Lumbricus rubellus living in non-polluted and heavily Zn-polluted soils were determined by fully quantitative electron probe X-ray microanalysis. P, Ca, S and Zn were the major elemental components of the chloragosomes. The in vivo accumulation of Zn by the chloragosomes was accompanied by diminished chloragosomal Ca concentrations. Zn was apparently bound by at least two ligand pools (Pool 1=uncharacterised; Pool 2=P-containing ligands, binding approximately 45% and 55% of the Zn, respectively) in the control chloragosomes. In Zn-contaminated chloragosomes, most (70%) was bound by P-containing ligand(s) but some (<1%) was also bound by S-containing ligands. It is suggested that the sequestration of Zn in chloragosomes results in the detoxification of the metal by accumulative immobilisation.     

The effect of lead incorporation on the elemental composition of earthworm (Annelida, Oligochaeta) chloragosome granules

The elemental compositions of chloragosome 'granules' in the earthworm Lumbricus rubellus living in non-polluted (Dinas Powys) and heavily Pb-polluted (Wemyss) soils were determined by fully quantitative electron probe X-ray microanalysis. P, Ca, S and Zn were the major elemental components of the chloragosomes. High Pb concentrations were found in chloragosomes of Wemyss animals; Pb was not detected in chloragosomes of Dinas Powys animals. Partial correlation and regression analysis indicated that the in vivo accumulation of Pb by chloragosomes was accompanied by diminished chloragosomal Ca concentrations. Pb is bound by P-containing ligand(s) in the chloragosome matrix. The sequestration of Pb by chloragosomes results in the detoxification of the metal by accumulative immobilization.     

The effect of lead incorporation on the elemental composition of earthworm (Annelida,Oligochaeta) chloragosome granules

Summary The elemental compositions of chloragosome granules in the earthworm Lumbricus rubellus living in non-polluted (Dinas Powys) and heavily Pb-polluted (Wemyss) soils were determined by fully quantitative electron probe X-ray microanalysis. P, Ca, S and Zn were the major elemental components of the chloragosomes. High Pb concentrations were found in chloragosomes of Wemyss animals; Pb was not detected in chloragosomes of Dinas Powys animals. Partial correlation and regression analysis indicated that the in vivo accumulation of Pb by chloragosomes was accompanied by diminished chloragosomal Ca concentrations. Pb is bound by P-containing ligand(s) in the chloragosome matrix. The sequestration of Pb by chloragosomes results in the detoxification of the metal by accumulative immobilization.     

Cold-stress induced formation of calcium and phosphorous rich chloragocyte granules (chloragosomes) in the earthworm Eisenia fetida

The cytochemical and functional characteristics of chloragocytes of both 'control' and cold-stressed Eisenia fetida were examined. Flow cytometry revealed the heterogeneity of chloragocytes: the first group was characterized by low, the second one by high acid phosphatase (AcP) content. In 'control' animals the former, in cold-stressed ones the latter type were the dominant form. The elevated AcP-activity correlated with the accumulation of autophagic vacuoles (AVs) in chloragocytes. Both AVs and all small chloragosomes showed high AcP activity, while most of the large chloragosomes did not display any. Most 'control' granules (0.75-1.25 μm) contained high amounts of Ca and P, with less and variable quantities of S, Cl, K, Fe and Zn. Small chloragosomes with low Ca and P concentrations were seldom found. In cold-stressed animals the number of small granules (0.25-0.75 μm) increased up to 40% of total population. Their Ca and P contents were significantly lower; S and Fe concentrations were higher than those of large chloragosomes (1.0-1.5 μm). Our results prove that the formation and elemental composition of chloragosomes can be influenced by environmental stressors and suggest that the mature chloragosomes are tertiary lysosomes and their formation is coupled to autophagocytosis.     

A morphological and electron-microprobe study of the inorganic composition of the mineralized secretory products of the calciferous gland and chloragogenous tissue of the earthworm,Lumbricus terrestris L.

Summary The two pairs of lobes of the calciferous gland of the earthworm Lumbricus terrestris are specialized oesophageal diverticulae that secrete spherites ranging from 0.5–7.0 m in diameter. Correlative transmission and scanning electron microscopy indicated that the spherites (which are predominantly CaCO₃) are formed extracellularly in distinctive bays bounded by secretory-cell processes, and are mobilized anteriorly from the gland lumina to the lumen of a non-secretory pouch, where the majority coalesce and undergo phase transformation to concretions 0.5–1.0 mm in diameter consisting of a mass of cuboidal crystals with facets up to 40 m. The distribution of Sr (0.1 ml 5 % SrCl₂ injected into the posterior coelomic cavity) was monitored in the mineralized secretory products of the calciferous glands by X-ray microanalysis of 10 m — thick air-dried cryostat sections in a SEM. Strontium was not detected in chloragosomes at 2 h and 24 h post-injection. Strontium was transported anteriorly and specifically incorporated into gland spherites (detectable within 2h). This technique of Sr localization afforded sufficient structural and analytical resolutions to provide a confirmation of the sequence of extracellular changes in the gland/pouch system. In addition we were able to distinguish a population of growing spherites from the vast majority of mature spherites; size alone was a singularly poor indication of spherite growth.The major element constituents of the chloragosomes were P, Ca and Zn (Ca: P ranging from 0.4 to 1.0; Zn: P from about 0.05 to 0.45). Analysis of individual spherites showed that Ca was probably bound to P or P-containing matrix components, whilst Zn was probably linked to one or more different but unknown constituents.     

The elemental composition of the chloragosomes of two earthworm species (Lumbricus terrestris and Allolobophora longa) determined by electron probe X-ray microanalysis of freeze-dired cryosections

Summary The elemental composition of the chloragosomes of the two earthworm species, one with complex highly active Ca-secreting calciferous glands (L. terrestris) and the other with non-secretory glands (A. longa), was determined by the electron probe X-ray microanalysis of unfixed freeze-dried cryosections. The predominant constituents of the chloragosomes of both species were P, Ca, Zn and S, with lesser quantities of K, Cl and Fe. The most striking species differences in chloragosomal chemistry were the higher concentrations (expressed as relative mass fractions) of P(×2.1), Ca(×1.5), and Zn(×2.3) in L. terrestris, and the much higher S(×19.6) in A. longa. These differences were discussed in relation to the general ecophysiology of the two species, and more specifically in relation to heavy metal uptake and binding.     

Subcellular localization of zinc in experimentally polluted tubifex tubifex (Annelida,Oligochaeta)

• 1.1. Localization of Zn (+ ⁶⁵Zn) has been examined within twelve subcellular fractions (derived from discontinuous sucrose gradients) of preincubated T. tubifex.
• 2.2. Zn was principally associated with the pellet (28% of total) and lowest density fraction (14%).
• 3.3. Pellet ultrastructure is composed of chloragosomes and epicuticle. Pellet Zn is localized within chloragosomes, X-ray microanalysis showing chloragosomal Zn concentration to exceed epiculticular Zn by a factor of thirty.
• 4.4. Biochemical and ultrastructural studies demonstrate that Zn is not appreciably bound to other cell constituents.
• 5.5. Chloragosomal localization of internalized Zn indicates a capacity for detoxification.

     

The accumulation and intracellular compartmentation of cadmium,lead, zinc and calcium in two earthworm species (Dendrobaena rubida and Lumbricus rubellus) living in highly contaminated soil

Summary The earthworm Lumbricus rubellus contained more Ca and Zn, and less Pb and Cd, than Dendrobaena rubida living in the same contaminated disused-mine soil. Differences in the kinetics of Ca turnover may account for some of the inter-specific differences in heavy metal burdens, although the calciferous glands do not seem to be directly involved in heavy metal excretion. A comparison of the present findings with published data indicated that the concentration of soil Ca and the bioavailability of heavy metals, both factors being allied to soil pH, are important exogenous determinants of heavy metal accumulation by different earthworm populations. Electron microprobe X-ray analysis of air-dried smears of chloragogenous tissue showed that the metals were fairly specifically compartmentalized into two distinct organelles in both worms: Ca, Pb and Zn were found (associated with P) in the chloragosomes; Cd was found (with S and probably in stoichiometric association) in a more electron-lucent vesicular component, designated the cadmosome, but which may be identical with the debris vesicles which are characteristic inclusions in conventionally-fixed chloragocytes. The in vivo incorporation of Pb by the chloragosomes of D. rubida was accompanied by the loss of Ca, Zn and P.     

Synthesis and characterisation of the first transition metal complex of zoxazolamine (2-amino-5-chlorobenzoxazole): the X-ray crystal structure determination of [ZnCl2(eta 1-Nbenzoxazole-2-amino-5-chlorobenzoxazole)2

The synthesis and characterisation (NMR, X-ray, elemental analysis) of the first transition metal complex of Zoxazolamine (1: 2-amino-5-chlorobenzoxazole), viz. [ZnCl(2)(1)(2)] (2) is described; complex 2 is obtained in 77% yield from the treatment of 1 with ZnCl(2) in acetone solution. The Zn compound is a mononuclear species (X-ray) with a distorted tetrahedral array of ligands around the metal centre with the title ligand bound to Zn via the benzoxazole ring N-atom. The structural properties of 2 are discussed in relation to other mononuclear Zn halide complexes.     

Mixture toxicity of copper and zinc to barley at low level effects can be described by the Biotic Ligand Model

Background and aims

The biotic ligand model (BLM) is a bioavailability model for metals based on the concept that toxicity depends on the concentration of metal bound to a biological binding site; the biotic ligand. Here, we evaluated the BLM to interpret and explain mixture toxicity of metals (Cu and Zn).

Methods

The mixture toxicity of Cu and Zn to barley (Hordeum vulgare L.) was tested with a 4 days root elongation test in resin buffered nutrient solutions. Toxicity of one toxicant was tested in presence or absence of a low effect level of the other toxicant or in a ray design with constant toxicant ratios. All treatments ran at three different Ca concentrations (0.3, 2.2 and 10?mM) to reveal ion interaction effects.

Results

The 50 % effect level (EC50) of one metal, expressed as the free ion in solution, significantly (p?<?0.05) increased by adding a low level effect of the other metal at low Ca. Such antagonistic interactions were smaller or became insignificant at higher Ca levels. The Cu EC10 was unaffected by Zn whereas the Zn EC10 increased by Cu at low Ca. These effects obeyed the BLM combined with the independent action model for toxicants.

Conclusions

The BLM model explains the observed interactions by accounting for competition between both metals free ions and Ca²⁺ at the Cu and Zn biotic ligands. The implications of these findings for Cu/Zn interactions in soil are discussed.     

Short and long spacer sequences and other structural features of zinc binding sites in zinc enzymes

The crystal structures of eleven zinc enzymes have served to identify common features of their Zn binding sites. Two of them have non-catalytic Zn sites, both of which contain four cysteine ligands closely spaced in the linear sequence of the protein with no bound water. In contrast, all the catalytic Zn sites have three protein ligands and, in addition, one coordinated, 'activated' water. Histidine is the predominant ligand. The spacing between the first two ligands (1-3 amino acids), the short spacer, ensures a nucleus for Zn binding. The third ligand, separated by from approximately 20 to approximately 120 amino acids, the long spacer, not only completes the coordination but also aligns protein residues for interaction with the substrate. The short and long spacing observed for catalytic zinc sites may also pertain to Fe and Cu proteins.     

Metals and phosphate in the chloragosomes of Lumbricus terrestris and their possible physiological significance

Summary The chloragog cells of the earthworm Lumbricus terrestris contain numerous granules, chloragosomes, which were analyzed for metals and phosphate by histochemistry, by use of an electron microscope X-ray microprobe (EMMA), and by chemical analysis of chloragosome preparations. Inorganic and organic phosphate each accounts for about 3% of the chloragosome dry mass, Ca for 2–3%, Zn for 1–3% and Mg for 0.2–0.4%. Carbonate is not present in chloragosomes. The average molar ratios CaMgZntotal PO₄ are 10.10.31. The CaPO₄ ratio is fairly constant (correlation coefficient 0.99), while the ZnPO₄ ratio varies considerably. It is concluded that Ca is bound in the form of inorganic CaHPO₄ and organic ROPO ₃Ca (or possibly Ca-polyphosphate complexes). Mg may also be phosphate-bound, while Zn probably is not. Chemical analysis of the calciferous glands revealed a high concentration of Ca, small amounts of Mg and phosphate, but no Zn. It is concluded that Zn is not excreted through the calciferous gland.Storage of Ca in the chloragocytes and excretion of CaCO₃ by the calciferous gland may be physiologically linked. Regulation of the concentrations of Ca and HCO₃ ^–ions in the blood and coelomic fluid may assist in equalization of osmotic pressures during dehydration and rehydration. This regulation may be a major function of the chloragosomes.The chloragosomes were discussed in relation to the spherites of various arthropods and molluscs and to the cytosomes of anoxia-tolerating molluscs.I wish to thank Theodore A. Hall for the use of the EMMA-4 microprobe facility, T.C. Norrnann for help in performing the microprobe analysis, Bruno Hansen for the improved zinc determination method and Annette Prentø for performing the chemical analyses. This work was supported by the Danish Natural Science Research Council (grant 511-3522). The EMMA-4 facility is supported by a grant from the British Science Research Council     

The binding of zinc in root cells of crop plants by phytic acid

Appreciable quantities of Zn are bound as Zn phytate (myo-inositol kis-hexaphosphate) within small vacuoles of cortical cells in the elongation zone of root tips of zinc tolerant Deschampsia caespitosa. These Zn/P-containing globular deposits have now been shown to occur in the roots of soybean, lucerne, lupins, tomato, rapeseed, cabbage, radish, wheat and maize. The globules are most frequent in the endodermis and pericycle but may also occur in the stele and inner cortex. The X-ray data again confirmed the presence of phytate with a relatively stable proportion of Zn and a species-dependent, variable, proportion of K, Mg and Ca to P.Analysis of soybean plants by atomic absorption spectroscopy showed that the Zn concentration in the shoots doubled in response to an increase in Zn supply from 1 to 100 M while the concentration of Zn in the root symplast was approximately 22 times greater than in the shoot, suggesting restricted transport to the shoot. It is suggested that the genetic expression of the capacity to bind heavy metals by means of phytate in endodermal cells may provide a strategy for keeping the above-ground content of heavy metals low. It may be possible to incorporate the trait into transformed roots that can be utilized for the treatment of industrial wastes.     

The mechanism of stabilization of the structure of nuclease-T by binding of ligands.

The rate of unfolding of Nuclease-T at pH 8,20 degrees was determined as a function of concentration of the ligands deoxythymidine 3',5'-diphosphate (pdTp) and Ca2+ on the basis of the rate of exchange between free fragment, Nuclease-T(50-149) and labeled fragment, Nuclease-T-(50-149) incorporated in the structure of nuclease-T (Taniuchi, H. (1973) J. Biol. Chem. 248, 5164-5174). The rate constant of unfolding of unliganded Nuclease-T' was 4.6 times 10-4s-1. Those of Nuclease-T' bound with pdTp, with Ca2+, and with both pdtp and Ca2+ were 9.0 times 10-5, 1.6 times 10-4, and 2.2 times 10-5s-1, respectively. The association constants of pdTp and Ca2+ with Nuclease-T' were found to be 1.0 times 10-4 and 2.0 times 10-2 m-1, respectively. Those of pdTp with Nuclease-T' plus Ca2+ and of Ca2+ with Nuclease-T' plus pdTp were 4 times 10-5 and 1.4 times 10-4M-1, respectively. The calculation of free energy change on the basis of the association constants shows that the magnitude of negative free energy change involved in the binding of either of the two ligands increases by approximately 2 kcal when the other ligand is already bound. There is a correlation between the free energy change and the specifically coupled with the cooperative interacions operating throught the three-dimensional structure resulting in strengthening of the interactions throughtout the structure, including those with the ligands, without a large change in conformation.     

Synthesis and structural characterization of silver(I), aluminium(III) and cobalt(II) complexes with 4-isopropyltropolone (hinokitiol) showing noteworthy biological activities. Action of silver(I)-oxygen bonding complexes on the antimicrobial activities

Through two unequivalent oxygen donor atoms of the hinokitiol (Hhino; C10H12O2; 4-isopropyltropolone) ligand that showed noteworthy biological activities, the dimeric, silver(I)-oxygen bonding complex [Ag(hino)]2 1, the monomeric aluminium(III) complex [Al(hino)3].0.5H2O 4 and the cobalt(II) complex "[Co(hino)2]2.H2O" 6 were synthesized and characterized with elemental analysis, thermogravimetric and differential thermal analysis (TG/DTA), FTIR and solution (1H and 13C) NMR spectroscopy. The crystal structure of 1 was determined by Rietveld analysis based on X-ray powder diffraction (XPD) data and those of [Al(hino)3].MeOH 4a and [Co(hino)2(EtOH)]2 6a, being obtained as yellow block crystals and red platelet crystals, respectively, by crystallization of 4 and 6, were determined by single-crystal X-ray analysis. The antimicrobial activities of 1, 4 and 6, evaluated with minimum inhibitory concentration (MIC; microg ml(-1)), were compared with those of other metal complexes (M=Na, Li, Cs, Ca, V, Zn) with the hino- ligand. The antimicrobial activities observed in the alkali-metal salts strongly suggested that they were attributed to the effect of the anionic hino- species. The antimicrobial activities of 1 were significantly enhanced, whereas those of other metal complexes were suppressed, compared with those of the neutral Hhino and anionic hino- molecules. The antimicrobial activities observed in 1 were comparable with those of other recently found silver(I)-oxygen bonding complexes, the ligands of which had no activity. Thus, it is proposed that the antimicrobial activities of the silver(I)-oxygen bonding complexes are due to a direct interaction or complexation of the silver(I) ion with biological ligands such as protein, enzyme and membrane, and the coordinating ligands of the silver(I) complexes play the role of a carrier of the silver(I) ion to the biological system.     

Crystal structure analysis of a recombinant predicted acetamidase/formamidase from the thermophile Thermoanaerobacter tengcongensis

The structure of acetamidase/formamidase (Amds/Fmds) from the archaeon Thermoanaerobacter tengcongensis has been determined by X-ray diffraction analysis using MAD data in a crystal of space group P2?, with unit-cell parameters a = 41.23 (3), b = 152.88 (6), c = 100.26 (7) ?, β = 99.49 (3) ° and been refined to a crystallographic R-factor of 17.4% and R-free of 23.7%. It contains two dimers in one asymmetric unit, in which native Amds/Fmds (TE19) contains of the 32 kDa native protein. The final model consists of 4 monomer (299 amino acids residues with additional 2 expression tag amino acids residues), 5 Ca2?, 4 Zn2? and 853 water molecules. The monomer is composed by the following: an N-domain which is featuring by three-layers β/β/β; a prominent excursion between N-terminal end of strand β? and β??, which contains four-stranded antiparallel β sheet; an C-domain which is formed by the last 82 amino acid residues with the feature of mixed α/β structure. The protein contains ion-pair Ca2?-Zn2?. The portion of three-layer β/β/β along with the loops provides four protein ligands to the tightly bound Ca2?, three water molecules complete the coordination; and provides five protein ligands to the tightly bound Zn2?, one water molecule complete the coordination.     

The calmodulin-dependent activation and deactivation of the phosphoprotein phosphatase, calcineurin, and the effect of nucleotides, pyrophosphate, and divalent metal ions. Identification of calcineurin as a Zn and Fe metalloenzyme

Studies on the interaction of calcineurin with its activator, calmodulin, showed that the 1:1 complex is the activated species. Concomitant with activation, a time-dependent deactivation of the phosphatase was observed. The process followed first order kinetics and was dependent on the presence of both Ca2+ and calmodulin. The deactivation rate constant at pH 7.6 and 30 degrees C was 0.06 min-1, which was increased by the substrate, p-nitrophenylphosphate (Km = 11 mM), to 0.47 min-1. PPi and nucleotides inhibited the enzyme competitively and accelerated the deactivation. The first order rate constant was increased to 2.3 min-1 by PPi (Ki = 55 microM) and to 8.0 min-1 by ADP (Ki = 0.94 mM). A theory dealing with the deactivation (applicable to chemical modification, etc.) of an enzyme in the absence and presence of various ligands is presented. The deactivated enzyme remained bound to calmodulin and was not reactivated by dissociation-reassociation of the calcineurin-calmodulin complex. Calcineurin was found to contain covalently bound phosphate; however, no difference in its content was detected upon deactivation, indicating that self-dephosphorylation was not involved. The deactivation could be reversed, as well as prevented, by divalent metal ions such as Ni2+ and Mn2+. Atomic absorption spectroscopy revealed nearly stoichiometric amounts of tightly bound Fe and Zn (but little other ions) on purified calcineurin, which remained bound during the calmodulin-dependent deactivation; removal of tightly bound metals is, therefore, not the cause of deactivation. Our results indicate that calcineurin is a metallophosphatase and not simply a Ca2+- and calmodulin-stimulated enzyme. In addition to the nondissociable Zn and Fe and the Ca2+ bound to the B subunit and calmodulin, the enzyme requires a divalent metal ion for structural stability and full activity.     

The different roles of metal ions and water molecules in the recognition and catalyzed hydrolysis of ATP by phenanthroline-containing polyamines

The phenanthroline bridging polyaza ligands L1, L2 and L3 can selectively and strongly bind nucleotides at physiological pH, and hence accelerate the hydrolysis rate of the bound ATP. It is interesting that a phosphoramidate intermediate at 2.88 ppm (should be added 5.63 ppm when compared with other models) was found in the hydrolysis process of L/ATP. By introduction of metal ions (critical Zn(2+) or hard Mg(2+), Ca(2+)) to the L/ATP system, recognition of the anionic substrates by the protonated ligands was greatly promoted. However, due to the different affinities of metal ions to the receptor and the substrate, ATP hydrolysis in Zn(2+)/L/ATP system and Mg(2+)(Ca(2+))/L/ATP system occurs through different mechanisms. By comparison with the M/ATP (M=Zn(2+), Mg(2+), Ca(2+)) system, the rates of ATP-hydrolysis in the Mg(2+)Ca(2+)/L/ATP system and the Zn(2+)/L/ATP system were enhanced and retarded, respectively. Moreover, the reasons contributing to large rate range of the L/ATP systems and M(2+)/L/ATP systems were given. The results show that metal ions vertically regulate the recognition and hydrolysis of ATP. On the other hand, water molecule participates in the hydrolysis reactions at different steps with different functions in the L/ATP systems and M(Zn(2+), Mg(2+), Ca(2+))L/ATP systems.     

Interaction of nucleotides and cations with the (Ca2+, Mg2+)-ATPase of sarcoplasmic reticulum as determined by fluorescence changes of bound 1-anilino-8-naphthalenesulfonate

The changes in fluorescence of 1-anilino-8-naphthalenesulfonate (ANS-) have been used to determine binding of ligands to the (Ca2+, Mg2+)-ATPase of sarcoplasmic reticulum vesicles, isolated from rabbit skeletal muscle. ANS- binds to sarcoplasmic reticulum membranes with an apparent Kd of 3.8 X 10(-5) M. The binding of ANS- had no effect on Ca2+ transport or Ca2+-dependent ATPase activity. EGTA, by binding endogenous Ca2+, increased the fluorescence intensity of bound ANS- by 10-12%. Subsequent addition of ATP, ADP, or Ca2+, in the presence or absence of Mg2+, reversed this change of fluorescence. The binding parameters, as determined by these decreases in fluorescence intensity, were as follows: for ATP, Kd = 1.0 X 10(-5) M, nH = 0.80; for ADP, Kd = 1.2 X 10(-5) M, nH = 0.89; and for Ca2+, Kd = 3.4 X 10(-7) M, nH = 1.8. The binding parameters for ITP and for the nonhydrolyzable analogue, adenyl-5'-yl-beta, gamma-methylene)diphosphate, were similar to those of ATP, but GDP, IDP, CDP, AMP, and cAMP had lower apparent affinities. Millimolar concentrations of pyrophosphate also decreased the fluorescence of bound ANS-, whereas orthophosphate caused a small (2-3%) increase in fluorescence in Ca2+-free media. Vanadate, in the presence of EGTA, decreased the fluorescence of bound ANS-with half-maximal effect at 4 X 10(-5) M. The changes of fluorescence intensity of bound ANS- appear to reflect conformational changes of the (Ca2+, Mg2+)-ATPase, consequent to ligand binding, with the low and high fluorescence intensity species corresponding to the E1 and E2 conformations, respectively. These appear to reflect similar conformational states of the (Ca2+, Mg2+)-ATPase to those reported by changes in intrinsic tryptophan fluorescence (DuPont, Y. (1976) Biochem, Biophys. Res. Commun. 71, 544-550).     

Distribution of unselectively bound ligands along DNA

Unselective and reversible adsorption of ligands on DNA for a model of binding proposed by Zasedatelev, Gursky, and Volkenshtein is considered. In this model, the interaction between neighboring ligands located at the distance of i binding centers is characterized by the statistical weight a(i). Each ligand covers L binding centers. For this model, expressions for binding averages are represented in a new simple form. This representation is convenient for the calculation of the fraction of inter-ligand distances of i binding centers f(d)(i) and the fraction of binding centers included in the distances of i binding centers f(bc)(i) for various types of interaction between bound ligands. It is shown that, for non-cooperative binding, contact cooperativity and long-range cooperativity, the fraction of the zero inter-ligand distance f(d)(0) is maximal at any relative concentration of bound ligands (r). Calculations demonstrate that, at low r, f(d)(0) approximately r . a(o), and f(d)(i) approximately r at 1 1/r-L, then f(d)(i) rapidly decreases with i at any r for all types of inter-ligand interaction. At high ligand concentration (r is close to r(max) = L(-1)), f(d)(0) is close to unity and f(d)(i) rapidly decreases with i for any type of inter-ligand interaction. For strong contact cooperativity, f(d)(0) is close to unity in a much lager r interval ((0.5-1) . r(max)), and f(d)(1) approximately a(o)(-1) at r approximately 0.5 . r(max). In the case of long-range interaction between bound ligands, the dependence f(d)(i) is more complex and has a maximum at i approximately (1/r-L)(1/2) for anti-cooperative binding. f(bc)(i) is maximal at i approximately 1/r-L for all types of binding except the contact cooperativity. A strong asymmetry in the influence of contact cooperativity and anticooperativity on the ligand distribution along DNA is demonstrated.