Interaction and aggregation of sodium aurothiomalate and poly L-lysine

This report describes the interaction and aggregation of sodium aurothiomalate with polylysine, a potentially useful property, both as a model for drug-protein interaction and as a means of reversibly immobilizing sodium aurothiomalate. Sodium aurothiomalate formed stable precipitates with polylysine at neutral pH, ionic strengths below 1M NaCl, and optimally, at sodium aurothiomalate to lysine ratios of less than one. The interaction could be demonstrated both by precipitation (which was sensitive to the size of polylysine polymer) and by using polylysine immobilized to Sepharose. Precipitation could be inhibited by addition of the organic thiomalate moiety alone. These findings indicate that the interaction of sodium aurothiomalate with polylysine is by electrostatic bonding of the thiomalate (mercaptosuccinate) moiety and the epsilon-amino groups of lysine residues. At suitable molar ratios this will link together many polylysine chains leading to precipitation. This represents a potentially valuable interaction for immobilization of the drug and in the formation of conjugates.