Acid stable protease inhibitor in ascites of ovarian carcinoma.

In patients with ovarian tumors, a novel protease inhibitor which is very stable in acid (AS-PI, acid stable protease inhibitor) was identified in the ascites and tumor fluid as well as in the urine and plasma. The highest AS-PI activity was observed in the tumor fluid of ovarian carcinomas (10.7 +/- 2.3 U/ml), followed by the ascites of ovarian carcinomas (8.2 +/- 4.2 U/ml). There was a significant difference in activity of the tumor fluid and ascites between malignant and benign tumors (p less than 0.005, p less than 0.05, respectively). The same antigenicity of AS-PI fractionated from ascites of ovarian carcinomas to urinary trypsin inhibitor was identified by double immunodiffusion and neutralization techniques. It migrated in the serum albumin fraction on immunoelectrophoresis. By gel filtration, the AS-PI in the ascites of ovarian carcinomas showed a molecular weight of 70000-80000. Two active components with molecular weights of 61300 +/- 2100 and 73300 +/- 2500 were detected by SDS polyacrylamide gel electrophoresis.