PubMed · 14941089
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J W PEDERSEN, B E BAKER. 1952-05-31. Hydrolysis.. https://doi.org/10.1038/169928a0
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The formation of electrostatic complexes between sodium caseinate and gum arabic (GA) was studied as a function of pH (2.0-7.0), using slow acidification in situ with glucono-delta-lactone (GDL) or titration with HCl. The colloidal behavior of the complexes under specific conditions was investigated using absorbance measurements (at 515 or 810 nm) and dynamic light scattering (DLS). In contrast to the sudden increase in absorbance and subsequent precipitation of sodium caseinate solutions at pH < 5.4, the absorbance values of mixtures of sodium caseinate and GA increased to a level that was dependent on GA concentration at pH 5.4 (pH(c)). The absorbance values remained constant with further decreases in pH until a sudden increase in absorbance was observed (at pH(phi)). The pH(phi) was also dependent upon the GA concentration. Dynamic light scattering (DLS) data showed that the sizes of the particles formed by the complexation of sodium caseinate and GA between pH(c) and pH(phi) were between 100 and 150 nm and these nanoparticles were visualized using negative staining transmission electron microscopy (TEM). Below pH(phi), the nanoparticles associated to form larger particles, causing phase separation. zeta-Potential measurements of the nanoparticles and chemical analysis after phase separation showed that phase separation was a consequence of charge neutralization. The formation of complexes between sodium caseinate and GA was inhibited at high ionic strength (>50 mM NaCl). It is postulated that the structure of the nanoparticles comprises an aggregated caseinate core, protected from further aggregation by steric repulsion of one, or more, electrostatically attached GA molecules.
An apparatus for continuous fractionation of peptides on the basis of amphoteric nature of sample peptides was developed. A tank (66.5 cm x 8 cm x 8 cm, L x W x H) was divided into 12 compartments by a thin agarose gel layer. A drain tube (5.5 cm in length and 0.7 cm in i.d.) was fixed through the bottom of each compartment to give a height of 4 cm from the bottom. The tank with 12 compartments and electrodes was referred to as an autofocusing unit. The peptide solution or water was delivered to the sample compartments of the first unit. The solutions drained from the first unit were successively delivered to the second and third units. To the electrodes of three units, a direct electric current was applied. By using the present apparatus, peptides in casein hydrolysate can be continuously fractionated at least for 5 h. Better resolution was obtained in the second and third units.
Tissue type plasminigen activator (t-PA) is one of the important proteolysis factors in the pathogenesis of pulpal inflammation. However, the mechanisms and signal transduction pathways involved in the production of t-PA in human pulp cells are not fully understood. The purpose of this study was to investigate the t-PA activity in human pulp cells stimulated with various pharmacological agents. IL-1alpha was used to evaluate t-PA activity in human pulp cells using casein zymography and enzyme-linked immunosorbent assay (ELISA). Furthermore, to search possible signal transduction pathways, p38 inhibitor SB203580, MEK inhibitor U0126, and phosphatidylinositaol 3-kinase (PI3K) inhibitor LY294002 were added to test how they modulated the t-PA activity. The main casein secreted by human pulp cells migrated at 70 kDa and represented t-PA. Secretion of t-PA was found to be stimulated with IL-1alpha during 2 day cultured period (p < 0.05). From the results of casein zymography and ELISA, SB203580, U0126, and LY294002 significantly reduced the IL-1alpha-stimulated t-PA production, respectively (p < 0.05). Our findings demonstrated that IL-1alpha enhance t-PA production in human pulp cells, and the signal transduction pathways p38, MEK, and PI3K are involved in the inhibition of t-PA. SB203580, U0126, and LY294002 suppress t-PA activity and may also have important implication for pharmacological intervention.