Characterization of a 54 kDa, α 1 Antitrypsin‐like Protein Isolated from Ascitic Fluid of an Endometrial Cancer Patient

A protein factor which stimulated [ 3 H]thymidine uptake into free hepatocytes prepared from normal mouse liver was detected in the ascitic fluid of gynecological cancer patients. The factor was subsequently further purified from the ascitic fluid of an endometrial cancer patient by DEAE‐Sephacel, Sephadex G‐150 and Phenyl‐Sepharose CL‐4B column chromatographies, and sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) showed a single protein band of 54,000 Da, designated tentatively as 54K ascitic protein (54K‐AP). 54K‐AP was similar to human Qt‐antitrypsin (α 1 ‐AT) in terms of SDS‐PAGE and immunological behavior, but was slightly different in terms of amino acid sequence and isoelectric point. Although 54K‐AP inhibited the activities of bovine trypsin and a‐chymotrypsin as did human α 1 ‐AT, 54K‐AP inhibited the plasminogen activator released from human endometrial cancer Ishikawa cells more efficiently than α 1 ‐AT. Because, in contrast to normal serum, the serum from the endometrial cancer patients stimulated [ 3 H]thymidine uptake into hepatocytes, the possibility arises that 54K‐AP could he produced hy the cancer host as a defence mechanism against the cancer.