Induction of proteolytic activity in serum by treatment with anionic detergents and organic solvents

Using casein plates as a sensitive assay for proteolytic activity, it was observed that sodium-dodecyl sulfate (SDS) and other anionic detergents induce caseinolysis when mixed with sera and plasma. Caseinolysis was dependent on the presence of plasminogen in the fluids and could be blocked by inhibitors of serine proteases and antibody to plasminogen. Similarly, organic solvents such as isopropanol induced caseinolysis after mixing with plasma, but not normal serum. Isopropanol dissociated complexes of alpha 1-antitrypsin or alpha 2-macroglobulin with trypsin preformed in vitro. As both SDS and organic solvents are widely used in biochemical investigations of biological fluids, attention should be paid to the possible induction of proteolysis.