Isolation and partial characterization of a proteinase inhibitor from human colorectal adenocarcinoma

A proteinase inhibitor has been isolated from human colorectal adenocarcinomas by extraction with a low-ionic-strength buffer and a combination of Con A-Sepharose, Sephadex G-200, DEAE-cellulose and chromatofocusing steps. The preparation appeared to be homogeneous upon gel exclusion chromatography and SDS-polyacrylamide gel electrophoresis and had an estimated molecular weight of 66,000. The inhibitor was able to bind and inhibit urokinase, plasmin, trypsin, tissue plasminogen activator and thrombin. The binding appeared to be stoichiometric and relatively fast. The isoelectric point of the protein was 4.6-4.7. The inhibitor did not crossreact with antisera elicited against alpha 2-macroglobulin, alpha 2-antiplasmin, antithrombin III or C1-inhibitor, but it did crossreact with an antiserum against alpha 1-antitrypsin in double immunodiffusion. The antiserum only partially attenuated the activity of the inhibitor. Whereas alpha 1-antitrypsin completely inhibited the amidolytic activity of elastase, the tumor inhibitor had no effect on elastase under the same conditions.