Heterogeneity of free alpha-subunit in term placenta.

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Abstract
Free .alpha.-subunit in normal term placenta was examined for MW, electric charge and ability to combine with standard hCG[human chorionic gonadotropin]-.beta. in comparison with extracellular free .alpha.-subunit and standard hCG-.alpha. dissociated from urinay hCG in vitro. The gel chromatography on Sephadex G-100 of the placental extract revealed 3 major immunoreactive hCG-.alpha. peaks, designated as P.alpha.-A (Kav = 0.32-0.46), P.alpha.-B (0.47-0.58) and P.alpha.-C (0.59-0.70), near the position of standard hCG-.alpha.. In the isoelectric focusing, while P.alpha.-A was mainly distributed over the acidic region, the major components of P.alpha.-B and P.alpha.-C were distributed over the basic region. Furthermore, in the combination study with standard hCG-.beta., such .alpha.-subunit with acidic pI [isoelectric point] scarcely showed any combining activity while .alpha.-subunit with basic pI revealed significant combining activity. Apparently the various size species of placental .alpha.-subunit may be responsible for the progressive glycosylation; the small .alpha.-subunit with basic pI may combine with .beta.-subuit to form immunoreactive hCG; the .alpha.-subunit, which has not associated with .beta.-subunit, may be converted to a large and incombinative form with acidic pI by further glycosylation, followed by secretion as a free .alpha.-subunit.

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