Abstract
An immunosuppressive substance was isolated from ascitic fluids of patients with advanced colon cancer by means of ammonium sulphate precipitation and preparative isoelectric focusing. This was a glycoprotein with an isoelectric point of pH 2.7-3.3, a molecular weight of about 52,000, and a sedimentation coefficient of 4.0S. The substance showed a single band on ordinary disc electrophoresis, but it was separated into several bands by gel isoelectric focusing, due to the structural variety of the sugar moiety. The results of physicochemical analysis indicate that the amino acid composition of this glycoprotein was indistinguishable from that of alpha 1-acid glycoprotein (alpha 1-AG), but its molecular weight, its carbohydrate content, and composition were distinctly different. Furthermore, this glycoprotein was found to have higher immunosuppressive activity than that of alpha 1-AG in both the in vitro and in vivo assays. This glycoprotein, which we called "IS substance," is a cancer-related substance synthesized in cancer patients.
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