Interactions of bovine serum albumin and lysozyme with sodium silicate solutions

The interaction of lysozyme and bovine serum albumin (BSA) with diluted solutions of sodium silicate was studied at pH 4.7 and 7.2. At neutral pH, lysozyme leads to the formation of a silica precipitate incorporating the protein whereas a composite BSA-silica gel was obtained in acidic media. Using the colorimetric molybdosilicate method, the nature of the silicate species interacting with the proteins could be determined. The effect of pH on these interactions is discussed, taking into account the evolution of the charge of both organic and inorganic components. Characterisation of the solids by thermogravimetric analysis, Si-29 magic angle spinning-NMR, electron microscopy and porosimetry confirms the proposed mechanisms of protein-silica interactions. Of particular interest is the fact that BSA-silicate interactions induce protein aggregation that controls silica particles size, mimicking biomincralization processes. (C) 2002 Elsevier Science B.V. All rights reserved.