EFFECT OF MEDIUM POLARITY ON THE REACTIVITY OF AMINO-ACIDS IN IMMOBILIZATION TO SILICA

The effect of medium polarity on the relative reactivity of the nucleophilic amino acids lysine, cystein and tyrosine has been investigated. It was found that, whereas lysine was most reactive in aqueous buffer, cystein had the highest reactivity in a water/oil (w/o) microemulsion, i.e. a medium of low polarity. The results indicate that the pattern of immobilization of proteins to solid surfaces may be governed by the choice of reaction medium. In a w/o microemulsion attachment via cystein residues is favoured from reactivity reasons, and binding via tyrosine residues is likely to be promoted by conformational changes, since the hydrophobic residues will strive for the outside of the protein molecule. The net result will be that immobilization via lysine residues is minimized, a fact which has important implications with regard to activity of the immobilized enzyme. © 1990.