The characterization of alpha-subunit of glycoprotein hormone produced by undifferentiated carcinoma.

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Abstract
The glycoprotein hormone .alpha.-subunit was extracted and purified from the urine of a patient with undifferentiated carcinoma producing isolated .alpha.-subunit. Its final specific immunoactivity was 0.92 (mg .alpha.-subunit/mg protein). The .alpha.-subunit exhibited virtually identical immunoantigenecity to hCG[human chorionic gonadotropin]-.alpha. antiserum with standard hCG-.alpha.. The MW of the .alpha.-subunit determined by gel chromatography on Sephadex G-100 was greater than that of standard hCG-.alpha. dissociated by urea in vitro. By sodium dodecyl sulfate disc electrophoresis, however the .alpha.-subunit moved faster than hCG-.alpha. separated by mercaptoethanol reduction. The amino acid composition of the .alpha.-subunit was quite similar to that of standard hCG-.alpha.. In the isoelectric focusing, the major components of the .alpha.-subunit from undifferentiated carcinoma and the .alpha.-subunit from urine of normal pregnant women (3rd trimester) were distributed over the range from pH 3.5-6.0, while standard hCG-.alpha. was distributed in the fractions ranging from pH 6.0-8.0. The result of a combination study in vitro indicated that both .alpha.-subunits from undifferentiated carcinoma and from urine of normal pregnant women did not actively combine with hCG-.beta.. The .alpha.-subunit secreted by undifferentiated carcinoma is virtually identical with standard hCG-.alpha. as the protein moiety but differs in regard to carbohydrate moiety; excess of .alpha.-subunit, which is not associated with .beta.-subunit, may have undergone some intracellular modification, and consequently, the electric charge of the freely secreted .alpha.-subunit changes and it no longer has the ability to combine with the .beta.-subunit.

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