A P-31 NMR-STUDY OF THE ADSORPTION OF BOVINE SERUM-ALBUMIN ON MONTMORILLONITE USING PHOSPHATE AND THE PARAMAGNETIC CATION MN2+ - MODIFICATION OF CONFORMATION WITH PH

The specific interfacial area of bovine serum albumin (BSA) adsorbed on montmorillonite was deduced from the ratio between the quantity of cations exchanged on adsorption of BSA and the quantity of protein bound. A paramagnetic cation, Mn2+, was used, and its release from the clay surface was followed by measuring the line broadening effect of displaced Mn2+ on the 31P NMR signal from orthophosphate in the solution. From experiments conducted at different protein/clay ratios and different pH, it was deduced: (i) that no more than one monolayer was adsorbed; (ii) that the specific interfacial area was the same at low and at high surface coverage; (iii) that below the isoelectric point (i.e.p.) the specific interfacial area of BSA increased with decreasing pH, with a constant surface coverage of the clay surface; and (iv) that above the i.e.p. the surface coverage of the clay decreased with further increases in pH. It is assumed that electrostatic interactions between the protein and the clay surface play a major role in these phenomena. The correlation with the behavior of extracellular enzymes in soils is emphasized. © 1992

Interactions between proteins and soil mineral surfaces: environmental and health consequences

Proteins have long been recognized as important compounds in the biogeochemical cycles of terrestrial ecosystems. They can, for example, provide a source of nitrogen for plants and soil microorganisms following proteolysis and ammonification. Extracellular enzymes liberated in soil are essential catalysts in the mobilization of carbon, nitrogen, phosphorus and sulphur from macromolecular organic matter. Proteins are also implicated in new environmental topics, such as soil carbon storage, horizontal transmission of spongiform encephalopathies and potential negative effects of insecticidal toxins released from transgenic plants

Conformational Changes of Bovine Serum Albumin Induced by Adsorption on Different Clay Surfaces: FTIR Analysis

International audienceInteractions between proteins and clays perturb biological activity in ecosystems, particularly soil extracellular enzyme activity. The pH dependence of hydrophobic, hydrophilic, and electrostatic interactions on the adsorption of bovine serum albumin (BSA) is studied. BSA secondary structures and hydration are revealed from computation of the Amide I and II FTIR absorption profiles. The influence of ionization of Asp, Glu, and His side chains on the adsorp-tion processes is deduced from correlation between p 2 H dependent carboxylic/carboxylate ratio and Amide band profiles. We quantify p 2 H dependent internal and external structural unfolding for BSA adsorbed on montmorillonite, which is an electronegative phyllosil-icate. Adsorption on talc, a hydrophobic surface, is less denaturing. The results emphasize the importance of electrostatic interactions in both adsorption processes. In the first case, charged side chains directly influence BSA adsorption that generate the structural transition. In the second case, the forces that attract hydrophobic side chains toward the protein-clay interface are large enough to distort peripheral amphiphilic helical domains. The resulting local unfolding displaces enough internal ionized side chains to prevent them from establishing salt bridges as for BSA native structure in solution. On montmorillonite, a particular feature is a higher protonation of the Asp and Glu side chains of the adsorbed BSA than in solution, which decreases coulombic repulsion

QUANTITATIVE ASPECTS OF THE P-31-NMR DETECTION OF MANGANESE IN PLANT-TISSUES

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