Precipitation of enzymes with reversible soluble-insoluble polymers is a simple approach which can be easily scaled up. This work reports investigations aiming at verifying the existence of specific interactions and complex formation between porcine trypsin and poly acrylic acids using spectroscopy techniques. The trypsin-polymer complex was insoluble at pH lower than 5, with a stoichiometric ratio polymer mol per protein mol of 1: 148. It took only a minute for the insoluble complex to form and it was redissolved modifying the pH of the medium. The enzymatic activity of trypsin was maintained even in the presence of the polymer and after precipitation poly acrylic acid presence protect the enzyme from itself degradation. The conditions of complex formation were studied using pure proteins that could be applied on porcine pancreas homogenates as an isolation strategy of trypsin. (C) 2009 Elsevier Ltd. All rights reserved.