Inhibitor of trypsin and chymotrypsin in cultures of HeLa cells.

An inhibitor of trypsin and chymotrypsin with apparent molecular weight of 68 000 and a mobility similar to alpha1-globulin on polyacrylamide gel electrophoresis, was isolated from serum-free supernatant preparations from HeLa cells. Immunoelectrophoresis assays indicated that the inhibitor differed serologically from known inhibitors of serine proteinases in plasma and urine but shared antigenic determinants with an unidentified protein in these body fluids and with an inhibitor recently isolated from cultures of lung.