Identification and characterization of serum protein in patients with ovarian cancer

A 36 kDa protein was isolated from the sera of patients with ovarian cancer and rabbit antisera to this protein were prepared. Precipitation test with these antisera detected an antigen with electrophoretic mobility corresponding to alpha-1-globulins and molecular weight of 36 kDa. Direct comparison of precipitating test systems showed that this antigen is not identical to the known carcinoembryonic, placental, and reactive proteins. Serum alpha-1-globulin was not detected in the sera of healthy humans, pregnant women, newborns, and in human adult and fetal visceral tissues at the level of precipitating test system sensitivity 1 mg/liter. It was detected in the sera of patients with ovarian cancer, in ovarian tumor (cancer) tissues, in the contents of ovarian tumor cavities, and in concentrated specimens of amniotic fluid. The antigen was not detected in ascitic fluid of patients with ovarian cancer, but it was present in 75% serum samples from these patients. The antigen was called serum oncoovarian alpha-1-globulin. SDS-PAAG electrophoresis showed that this antigen is an oligomer consisting of subunits (monomers) with molecular weight of 36 kDa. Under denaturing conditions in the presence of 2-mercaptoethanol these monomers dissociate into polypeptide chains with a molecular weight of 18 kDa. The protein is liable to oligomerization. Comparative characteristics of serum oncoovarian alpha-1-globulin and CA-125 antigen are presented.