Calcium Bridges Research Articles

Effects of salts on rheological behaviour of salvia hydrogels

Rheological behavior of natural hydrogel produced from seeds of threeSalvia spp. (S. miltiorrhiza (SM),S. sclarea (SS), S.viridis (SV)) was investigated by using a Rheometer equipped with a cone and plate geometry measuring system under never-dried condition. Different chemical contents of such hydrogels give significant effects on their rheological properties. Because of incomplete penetration of water inside the hydrogels after drying before-dried hydrogels were used for rheological analysis. To know molecular interactions which predominated in the gel formation, some constituents were externally added to the 1.0% (w/w) hydrogel. Addition of urea to disrupt hydrogen bonds reduced 3.4-67% viscosity of the untreated hydrogels and changed viscoelastic properties from gel to liquid-like behavior. Neutral salts added to the hydrogel solution at 0.1 M also lowered the viscosity in a manner related with increase in size of cations and temperature. Changing from gel state to liquid-like state was also easily confirmed by oscillation measurement (storage,G′, and loss,G′⇔’, modulii) typically observed in the cases of potassium sulfate and potassium thiocyanate. Influence of pH variation on the viscosity explained that weak alkaline condition (pH 8-9) creates a higher resistance to flow due to increasingly electrostatic repulsions between negative charges (COO-). Importance of calcium bridges was also demonstrated by recovery of viscosity of the hydrogels by addition of calcium after acidification. The summarized results indicate that electrostatic repulsion is a major contributor for production of hydrogel structure.

Development of nanoparticulate drug delivery systems based on thiolated poly(acrylic acid)

In this study the preparation and stabilization of poly(acrylic acid)-cysteine nanoparticles and incorporation of a fluorescence marked model-compound was investigated. Nanoparticles were prepared by ionic gelation of a poly(acrylic acid)-cysteine conjugate with calcium chloride. Poly(acrylic acid)-cysteine nanoparticles display high cohesive properties due to a cross-linking process via calcium bridges in the core and the pervasive formation of disulphide bonds and were 139 ± 34 nm in size. Nanoparticles were loaded with FITC-dextrans (flourescein isothiocyanate-dextrans) of 4, 20 and 40 kDa molecular mass as model-compound via sonication method or via vibration method for 3 and 24 h. In vitro release studies showed an initial burst release followed by an extended release of model-compounds. The lower the molecular mass of the FITC-dextrans, the higher was the amount of incorporated and released model compounds. Vibration seems to be a proper method for the incorporation of hydrophilic and macromolecular drugs in poly(acrylic acid)-cysteine nanoparticles.

The Crystal Structure of Calcium-bound Annexin Gh1 from Gossypium hirsutum and Its Implications for Membrane Binding Mechanisms of Plant Annexins

Plant annexins show distinct differences in comparison with their animal orthologues. In particular, the endonexin sequence, which is responsible for coordination of calcium ions in type II binding sites, is only partially conserved in plant annexins. The crystal structure of calcium-bound cotton annexin Gh1 was solved at 2.5 A resolution and shows three metal ions coordinated in the first and fourth repeat in types II and III binding sites. Although the protein has no detectable affinity for calcium in solution, in the presence of phospholipid vesicles, we determined a stoichiometry of four calcium ions per protein molecule using isothermal titration calorimetry. Further analysis of the crystal structure showed that binding of a fourth calcium ion is structurally possible in the DE loop of the first repeat. Data from this study are in agreement with the canonical membrane binding of annexins, which is facilitated by the convex surface associating with the phospholipid bilayer by a calcium bridging mechanism. In annexin Gh1, this membrane-binding state is characterized by four calcium bridges in the I/IV module of the protein and by direct interactions of several surface-exposed basic and hydrophobic residues with the phospholipid membrane. Analysis of the protein fold stability revealed that the presence of calcium lowers the thermal stability of plant annexins. Furthermore, an additional unfolding step was detected at lower temperatures, which can be explained by the anchoring of the N-terminal domain to the C-terminal core by two conserved hydrogen bonds.

Egg box conformation of oligogalacturonides: The time-dependent stabilization of the elicitor-active conformation increases its biological activity

Circular dichroism spectrometry was used on oligogalacturonides (OGAs) and showed the existence of a calcium/sodium-induced conformational state that is intermediate between single-isolated chains and calcium-associated multimer chains. This conformation is interpreted as being egg box dimers. Using the 2F4 monoclonal antibody that specifically binds such an egg box dimer conformation of pectin, the stability of OGA dimers was investigated over a period of 24 hours. The extent to which egg box dimers were recognized by the antibody was dependent on the temperature and duration of preincubation of the OGA. This suggests a "maturation" process of the egg-box structure that consists in a progressive increase in the length of the junction sequences between two chains that slide along each other in order to form a maximum number of calcium bridges and dimer ends. The maturation of egg boxes induced both a significant increase in their binding to wall-associated kinase 1 (WAK1) and an increased extracellular alkalinization when applied to Arabidopsis thaliana cell suspensions. The chemical modification of the reducing end of the OGAs largely diminished their elicitating activity but did not hinder either dimerization or binding of these end-reduced egg boxes to WAK1. We conclude that there are at least two different perception systems for egg box dimers. One binds egg box junctions and the other binds egg box ends. The relevance of these results is discussed in terms of pectic signal perception and plant-pathogen interaction.

Copper 5-sulfoisophthalato quasi-planar squares in coordination polymers modulated by alkaline-earth metals: a way to molecular squares?

Two copper-sip coordination polymers (sip3− = 5-sulfoisophthalic anion), [Ca(H2O)3Cu2(H2O)6(sip)2]·2H2O 2a, and [Sr(H2O)4Cu2(H2O)6(sip)2]·H2O 2b, have been synthesized at room temperature. Single-crystal X-ray diffraction reveals that the structures of complexes 2a and 2b are 2-D coordination layer structures, containing [Cu4(sip)4] molecular squares linked by calcium (2a) or strontium (2b) bridges. The coordination layers display 3,6-connected topologies if the [Cu4(sip)4] molecular squares and alkaline-earth metals are considered as nodes, or (4,4) nets if alkaline-earth metals are considered to be part of the [Cu4(sip)4] squares. In comparison with the more commonly encountered Cu-sip zigzag chain subunits in copper-sip coordination polymers, the [Cu4(sip)4] square subunits in 2a and 2b represent similar coordination fashions and connecting modes while creating singular examples of new subunits in coordination complexes of the copper-sip system. Variable temperature magnetic susceptibility of 2a indicated that antiferromagnetic interactions dominate between the Cu(II) ions bridged by sip3− ligands.

Calcium bridges in fatty acid/pectin assemblies

Pectins are anionic polysaccharides arising from plant cell walls. Due to their charge, modulated by the degree of esterification, they are sensitive to cations, a property that is widely used in food science. Besides their gelling properties in bulk systems, little is known as regards their effect on interfacial films that constitute dispersed systems such as emulsions and foams. On the contrary, fatty acids are well known to form more or less condensed films at interfaces in the presence of calcium. By means of basic tools such as Langmuir Balance and a Brewster angle microscope, we demonstrate that pectin molecules are able to bind through calcium bridges to fatty acid films formed at the air–water interface. The interfacial behaviour of these new aggregates is controlled by the degree of charge of pectin and the calcium concentration.

Cultivar-Dependent Cell Wall Modification of Strawberry Fruit under NaCl Salinity Stress

Strawberry cultivars differ in their sensitivity to NaCl; fruits of cv. Elsanta suffer from softening, whereas those of cv. Korona retain their firmness. The mean fruit fresh weight is reduced in cv. Elsanta up to 46% and in cv. Korona up to 26%. Cell walls of fruits grown under 0, 40, or 80 mmol/L NaCl were extracted and analyzed. In fruits of cv. Korona, the content of the alcohol-insoluble residue remained comparatively stable as salt levels increased but was reduced in cv. Elsanta. The water-soluble pectin fraction was not affected in cv. Korona, but the content of low methoxy pectinates increased significantly, indicative of the generation of calcium and magnesium bridges that stabilize pectin polysaccharides of cell walls. In cv. Elsanta, the content of water-soluble pectin rose, indicating pectin solubilization. For both cultivars, the significant negative correlation of fruit Cl(-) contents with the contents of NaOH-soluble pectinates, when expressed per fruit fresh mass, indicated that covalently bound pectic substances were degraded. Especially the response of cv. Elsanta is in line with the general observation that severe osmotic stress results in slower cell expansion and weaker cell walls.

Biodegradation of forest floor organic matter bound to minerals via different binding mechanisms

Mineral-associated organic matter (OM) represents a large reservoir of organic carbon (OC) in natural environments. The factors controlling the extent of the mineral-mediated OC stabilization, however, are poorly understood. The protection of OM against biodegradation upon sorption to mineral phases is assumed to result from the formation of strong bonds that limit desorption. To test this, we studied the biodegradation of OM bound to goethite (α-FeOOH), pyrophyllite, and vermiculite via specific mechanisms as estimated from OC uptake in different background electrolytes and operationally defined as ‘ligand exchange’, ‘Ca 2+ bridging’, and ‘van der Waals forces’. Organic matter extracted from an Oa forest floor horizon under Norway spruce ( Picea abies (L.) Karst) was reacted with minerals at dissolved OC concentrations of ∼5–130 mg/L at pH 4. Goethite retained up to 30.1 mg OC/g predominantly by ‘ligand exchange’; pyrophyllite sorbed maximally 12.5 mg OC/g, largely via ‘van der Waals forces’ and ‘Ca 2+ bridging’, while sorption of OM to vermiculite was 7.3 mg OC/g, mainly due to the formation of ‘Ca 2+ bridges’. Aromatic OM components were selectively sorbed by all minerals (goethite ≫ phyllosilicates). The sorption of OM was strongly hysteretic with the desorption into 0.01 M NaCl being larger for OM held by ‘Ca 2+ bridges’ and ‘van der Waals forces’ than by ‘ligand exchange’. Incubation experiments under aerobic conditions (initial pH 4; 90 days) revealed that OM mainly bound to minerals by ‘ligand exchange’ was more resistant against mineralization than OM held by non-columbic interactions (‘van der Waals forces’). Calcium bridges enhanced the stability of sorbed OM, especially for vermiculite, but less than the binding via ‘ligand exchange’. Combined evidence suggests that the extent and rate of mineralization of mineral-associated OM are governed by desorption. The intrinsic stability of sorbed OM as related to the presence of resistant, lignin-derived aromatic components appears less decisive for the sorptive stabilization of OM than the involved binding mechanisms. In a given environment, the type of minerals present and the solution chemistry determine the operating binding mechanisms, thereby the extent of OM sorption and desorption, and thus ultimately the bioavailability of mineral-associated OM.

A comparative study of the flocculation behaviour and final properties of synthetic and activated sludge in wastewater treatment

In this study, we have investigated in a comparative fashion the flocculation behaviour and final properties of both synthetic and activated sludge. Synthetic sludge was prepared according to established procedures; activated sludge was produced in a lab-scale, continuous-flow reactor which was fed with live activated sludge from a wastewater treatment plant. The novelty of our approach lies in the attempt to use the former as a key to characterising the physical and chemical properties of the latter. The effects of calcium ion concentration on flocculation dynamics for both sludges were measured on-line using the photometric dispersion analyser; the effects of calcium, polyelectrolyte conditioner and shear rate on final sludge properties were determined, including settleability, turbidity of supernatant, sludge volume index and dewatering, sludge conditioning, and floc strength and structure. It was thus possible to link the flocculation dynamics to the final sludge properties. The results indicate that calcium ions play an important role in the floc formation and the final floc size for both types of sludge by the construction of calcium bridges, and hence played a significant role in determining the final properties of the sludge. A qualitative link exists between the flocculation dynamics and the final properties for both types of sludge, and between the floc dynamics and properties of synthetic sludge on the one hand and those of activated sludge on the other. The two types of sludge have very similar settling and dewatering characteristics after cationic polymer conditioning. However, there are quantitative differences in the calcium concentration required for flocculation, the supernatant turbidity, the sludge-volume index and the floc strength. This difference is believed to be due to the absence of filamentous material in the synthetic sludge which is present in the activated sludge. The stable and well-defined nature of synthetic sludge makes it useful as a non-complex analogue for the physical and chemical properties of activated sludge, but filamentous cellulose should be added to improve quantitative agreement with activated sludge.

Molecular modeling of some calcium and magnesium ionic bridges

AbstractBond length and atomic charges are calculated for L2M and L2M2+ complexes, as well as dissociation energies in vacuum for the complexes, with semiempiric ZINDO1 and PM3 methods, and with ab initio method with 3‐21G and 6‐31G* basis sets. Here, L are CH3COO−, CH3OSO, ethylenediol and 1,4‐dioxane; M2+ are Ca2+ and Mg2+. Geometries for CH3COO− and 1,4‐dioxane are in fair agreement with X‐ray crystallographic data. Dissociation energies calculated by ab initio, are in the range of 200–500 kcal/mol, generally larger for Mg2+ then for Ca2+‐complexes. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007

Effect of New Photocatalytic Coagulant on NF Membrane Fouling

In this research, the results of the photocatalytic coagulation of humic acids (HAs) in aqueous solution were investigated, and the effect of the photocatalytic coagulation on the fouling of nanofiltration (NF) membrane was investigated. Nanoparticles of copper-doped titania were synthesized by a sol−gel method using titanium isopropoxide and cuperous chloride. The behavior of a thin-film composite NF membrane was investigated as a function of solution chemistry (ionic composition and strength and calcium and organic concentration). In the membrane fouling test, calcium bridges between the natural organic matter (NOM) and the membrane led to severe flux decline because of the development of densely compacted fouling layer on the membrane surface. The photocatalytic coagulation was applied to remove humic acids prior to membrane filtration. In the photocatalytic coagulation, the UV absorbance, chemical oxygen demand (COD), and cations decreased by 99%, 90%, and 10%, respectively, while anions and conductivity increased to 39% and 79%. The results emphasized that the photocatalytic coagulation could be an effective alternative solution for the elimination of the humic acids and for the prevention of the membrane fouling.

The effect of calcium on the membrane biofouling in the membrane bioreactor (MBR)

A continuous bench-scale submerged membrane bioreactor (BSMBR) was operated in two modes; low (LC) and optimum calcium (OC) concentrations, to investigate the effect of calcium on membrane biofouling. Both the cake layer and pore blocking resistances were reduced in the operation under OC conditions. In order to find the causes of fouling, molecular weight fractionations of the extracellular polymeric substances (EPS) and soluble microbial products (SMP) were conducted, and the relative hydrophobicity of the sludge, EPS and SMP were also measured. The reduction in the cake layer resistance was assumed to be due to the decrease of filamentous bacteria, and better flocculation caused by the calcium bridges and the increased hydrophobicity of EPS in the operation under OC conditions. It was suggested that the pore blocking resistance was reduced due to the low SMP rejection of the membrane and the fewer hydrophobic reactions of the SMP in the operation under OC conditions. Fourier-transform infrared analysis of the fouled membrane surface supported that proteins and carbohydrates were the main foulants during the BSMBR operation.

Interfacial Interaction between Dextran Sulfate and Lipid Monolayers: An Electrochemical Study

The interaction between dextran sulfate (DS) with zwitterionic dipalmitoylphosphatidylcholine (DPPC) and negatively charged dipalmitoylphosphatidic acid monolayers at different surface pressures at air-liquid and liquid-liquid interfaces was studied using Langmuir-Blodgett (LB) and electrochemical techniques. The negatively charged DS can bind to phospholipids via calcium ions. To investigate the mechanism of the adsorption of DS on lipid monolayers, compression isotherms (pi-A) and capacitance-potential curves were measured, and a theoretical model was developed to interpret the capacitance data. The compression of lipid monolayers in the presence of DS led to a more condensed hybrid layer, removing the LE-LC phase transition of DPPC. Lower surface pressures improved the binding of DS on the lipid monolayers via calcium bridges due to the electrostatic attraction. Alternating current voltammetry and cyclic voltammetry were used to monitor the transfer of a cationic beta-blocker (metoprolol) across lipid monolayers in the absence and presence of the polyelectrolyte and to compare with the transfer of the standard probe, tetraethylammonium cation. Results showed a strong dependence on (i) the surface pressure, (ii) the applied potential, and, (iii) in the case of the hybrid layer, the charge of the phospholipid headgroup. Finally, results were also confirmed by attenuated total reflection Fourier transform infrared spectroscopy, performed after transferring lipid multilayers onto a solid substrate by the LB method.

Wall-associated Kinase WAK1 Interacts with Cell Wall Pectins in a Calcium-induced Conformation

Wall-associated kinase 1 (WAK1) is a transmembrane protein containing a cytoplasmic Ser/Thr kinase domain and an extracellular domain in contact with the pectin fraction of the plant cell walls. In order to characterize further the interaction of WAK1 with pectin, a 564 bp DNA sequence corresponding to amino acids 67-254 of the extracellular domain of WAK1 from Arabidopsis thaliana was cloned and expressed as a soluble recombinant peptide in yeast. Using enzyme-linked immunosorbent assays (ELISA), we show that peptide WAK(67-254) binds to polygalacturonic acid (PGA), oligogalacturonides, pectins extracted from A. thaliana cell walls and to structurally related alginates. Our results suggest that both ionic and steric interactions are required to match the relatively linear pectin backbone. Binding of WAK(67-254) to PGA, oligogalacturonides and alginates occurred only in the presence of calcium and in ionic conditions promoting the formation of calcium bridges between oligo-and polymers (also known as 'egg-boxes'). The conditions inhibiting the formation of calcium bridges (EDTA treatment, calcium substitution, high NaCl concentrations, depolymerization and methylesterification of pectins) also inhibited the binding of WAK(67-254) to calcium-induced egg-boxes. The relevance of this non-covalent link between WAK(67-254) and cell wall pectins is discussed in terms of cell elongation, cell differentiation and host-pathogen interactions.

Effects of pH, Ionic Strength, Calcium, and Molecular Mass on the Arrangement of Hydrophobic Peptide Helices at the Air−Water Interface

The influence of subphase characteristics (ionic strength, pH, and the presence of bridging cations) on the conformation and lateral orientation of the hydrophobic polypeptide poly-l-leucine (p-leu) has been investigated at the air−water interface with the surface film balance technique as well as with Brewster angle microscopy (BAM). In addition, Langmuir−Blodgett films of p-leu deposited on quartz and mica from different subphases have been studied by circular dichroism (CD) spectroscopy and atomic force microscopy (AFM). P-leu forms α-helices at the interface regardless of subphase characteristics. Long-range lateral orientation of the α-helical strands in the p-leu monolayer was obtained under conditions where attractive interpeptide end-group interactions prevail. These interactions were obtained under conditions where (1) end-group charges lend a zwitterionic character to the peptide, thus enabling strong electrostatic attraction between adjacent strands, (2) there is a possibility for formation of carboxylic acid dimers, or (3) calcium bridges form between carboxylate end groups. These three cases correspond to an increase of the effective molecular mass of the peptide. It was concluded that such an increase, and thereby an increased long-range lateral orientation, can be obtained by enabling peptide end group attraction, but not by screening peptide end group repulsion. Kinetic studies of monolayer relaxation strongly suggest that the end-group effects influence the thermodynamic, as well as the kinetic, properties of peptide monolayers.

Physical alginate hydrogels based on hydrophobic or dual hydrophobic/ionic interactions: Bead formation, structure, and stability

Hydrophobically associating alginate (AA) derivatives were prepared by covalent fixation of dodecyl or octadecyl chains onto the polysaccharide backbone (AA-C 12/AA-C 18). In semidilute solution, intermolecular hydrophobic interactions result in the formation of physical hydrogels, the physicochemical properties of which can be controlled through polymer concentration, hydrophobic chain content, and nonchaotropic salts such as sodium chloride. The mechanical properties of these hydrogels can then be reinforced by the addition of calcium chloride. The combination of both calcium bridges and intermolecular hydrophobic interactions leads to a decrease in the swelling ratio accompanied by an increase of elastic and viscous moduli. Beads made of hydrophobically modified alginate were obtained by dropping an aqueous solution of alginate derivative into a NaCl/CaCl 2 solution. As compared to unmodified alginate beads, modified alginate particles proved to be stable in the presence of nongelling cations or calcium-sequestering agents. However, evidence is presented for a more heterogeneous structure than that of plain calcium alginate hydrogels with, in particular, an increase in the effective gel mesh size, as determined by partition and diffusion coefficient measurements.

Textural, histological and biochemical changes in cucumber (Cucumis sativus L) due to immersion and variations in turgor pressure

AbstractTextural, histological and biochemical characteristics of cucumber (Cucumis sativus L) under different tissue turgor pressures were studied after equilibration of mesocarp tissue cylinders in various polyethylene glycol 400 (PEG) solutions. Tissue swelling was observed for all hypotonic solutions. Cell membrane vitality was detected in all cucumber tissues where significant values of initial firmness (fi) and residual relaxation force (FR) were found. Good turgor status was also associated with higher values of these parameters, observing higher values of the textural parameters for higher turgor. Cell wall integrity was observed through Calcofluor fluorescence assay in tissue equilibrated in hypotonic, isotonic and hypertonic solutions, although a lower fluorescence intensity was observed in tissue equilibrated with 0 mol m−3 PEG solution, probably owing to some cell bursting. Calcium bridges between pectic polymers were proven to be responsible for cell–cell adhesion and tissue integrity of cucumber mesocarp tissue. Compression curves obtained for raw tissue showed a stage of fracture, and its loss after immersion might be attributed to cell–cell adhesion weakness due to immersion in calcium‐free PEG solutions. Peroxidase and polygalacturonase increased after cucumber equilibration in the solutions, probably expressing tissue injury. Cucumber textural behaviour was very much affected by immersion in calcium‐free solutions, determining the loss of fracture stage and a great influence of turgor pressure on the textural response of soaked tissue.© 2003 Society of Chemical Industry

Autolysis-like release of homogalacturonan from bean ( Phaseolus vulgaris L.) callus cell walls

After 12 h incubation at 35 °C, cell walls isolated from bean calluses released approximately 3% of the cell wall dry weight as pectic polysaccharides (2.7%), largely composed of a t-1,2-diaminecyclohexane- N, N, N′, N′-tetraacetic acid-soluble homogalacturonan, and monosaccharides (0.3%). The release of sugars occurred over a broad pH range and was affected by the type of buffer used in cell wall incubation. The effect of the addition of calcium and chelators on the amount of released sugars indicated that the homogalacturonan was released by the cleavage of calcium bridges rather than an enzymatic reaction. This result is likely to be a consequence of the high amount of loosely-bound pectins in the cell walls of calluses. The monosaccharide fraction was exclusively composed of neutral sugars, mainly glucose. It seems reasonable to postulate that most of these monosaccharides would have been released in a reaction mediated by enzymes since the highest enzymatic activity detected in these cell walls corresponded to a β- d-glucosidase. A very small peak of released sugars at pH 5.5 is also consistent with an autolysis mediated through enzymes associated with the cell walls. The results presented suggest that the mechanism of sugar release from incubated bean cell walls varies with the cell wall composition and structure.

Thermodynamic compatibility of sodium caseinate with different pectins. Influence of the milieu conditions and pectin modifications.

Combinations of pectins and caseins are ingredients of many food products. Therefore the thermodynamic compatibility of both components was examined to investigate the influences of environmental factors as well as of the structure of the pectin. High-methoxyl pectin was demethoxylated and amidated, respectively, and tested for the compatibility with sodium caseinate under varying conditions of pH and ionic strength. The compatibility increased with increasing pH and decreasing ionic strength. Demethoxylated pectins were more and amidated pectins less compatible with the caseinate. Changes in the pectin hydrophilicity, solubility and molecular weight and possibly local interactions such as electrostatic attraction, hydrogen bonding and calcium bridges are involved in the compatibility of the components. The type and degree of the pectin modifications as well as the type, composition and properties of the protein were found to be of great importance for the thermodynamic compatibility.

Molecular Mechanism of the Renneting Process of Casein Micelles in Skim Milk, Examined by Viscosity and Light-Scattering Experiments and Simulated by Model SCF Calculations

The properties of the outer hairy layer of casein micelles have been studied using several methods. Viscosity and light-scattering measurements have been performed on rennet-destabilized skim milk at different concentrations of calcium. We have reproduced the known result that calcium promotes destabilization at relatively high κ-casein surface coverages (even at only 50% of the κ-casein molecules cut off). This suggests that calcium bridges contribute to the casein micelle attraction. The effect may be direct by calcium-mediated bridging of β-casein or αs1-casein (phosphate/carboxylate) or κ-casein (carboxylate) or indirect by altering the interplay between several types of caseins in the micelle. In the analysis of the experiments, we make use of an adhesive hard sphere approximation. The casein hairy layer has further been modeled by a self-consistent field (SCF) theory in which coarse-grained molecular details were included. In these calculations the effect of calcium bridges cannot directly be accounted for. It is shown that a κ-casein layer induces repulsive interactions of mainly steric origin. Cutting the N-terminus part results in reduced (shorter-ranged) repulsive pair potentials, which still dominate over the van der Waals attraction. As a result of the altered interplay between the several types of casein molecules during the renneting process, the αs1-casein concentration in the outer hairy layer may increase. Again using the SCF model, but now using a less-detailed description of the system, we examine a possible result of this. We confirm that diblock copolymers (simple model for κ-casein) and diblock copolymer with shorter soluble block (simple model for para-κ-casein) give repulsion and triblock copolymers (simple model for αs1-casein) give attraction by means of bridging (adsorption). The renneting process is simulated by increasing the ratio of model para-κ-casein to κ-casein at a fixed αs1-casein concentration. As a result, the potential shifts from repulsive to attractive. We show that by reducing the range of repulsive interactions of the diblock copolymers, we can make room available to express the attractive contributions of the model αs1-casein. This comprises a novel molecular-based mechanism for the renneting process.