Abstract
The glycoprotein hormone α-subunit was extracted and purified from the urine of a patient with undifferentiated carcinoma producing isolated α-subunit. Its final specific immunoactivity was 0.92 (mg α-subunit/mg protein). The α-subunit exhibited virtually identical immunoantigenecity to hCG-α antiserum with standard hCG-α. The molecular weight of the α-subunit determined by gel chromatography on Sephadex G-100 was greater than that of standard hCG-α dissociated by urea in vitro. By SDS disc electrophresis, however, the α-subunit moved faster than hCG-α separated by mercaptoethanol reduction. The amino acid composition of the α-subunit was quite similar to that of standard hCG-α. In the isoelectric focusing, the major components of the α-subunit from undifferentiated carcinoma and the α-subunit from urine of normal pregnant women (third trimester) were distributed over the range from pH3.5 to 6.0, while standard hCG-α was distributed in the fractions ranging from pH6.0 to 8.0. The result of a combination study in vitro indicated that both α-subunits from undifferentiated carcinoma and from urine of normal pregnant women did not actively combine with hCG-β.
These results suggest that the α-subunit secreted by undifferentiated carcinoma is virtually identical with standard hCG-α as the protein moiety but differs in regard to carbohydrate moiety, and also suggest that the excess of α-subunit, which is not associated with β-subunit, may have undergone some intracellular modification, and consequently, the electric charge of the freely secreted α-subunit changes and it no longer has the ability to combine with the β-subunit.
