Structure and significance of human luteinizing hormone-beta core fragment purified from human pituitary extracts.

A fragment of the hCG beta-subunit is present in high concentrations in the urine of pregnant women and the urine from individuals with ovarian or other cancers. The utility of immunoreactive measurement of this fragment to monitor therapy of such cancers is compromised, however, because high concentrations of the molecule are also detected in the urine of healthy postmenopausal women. It has been suggested that the latter observations may be due to a cross-reacting human (h) LH beta core fragment, presumably of pituitary origin, but no such fragment had ever been isolated. We have now isolated a hLH beta core fragment from a pituitary tissue extract. Its structure is exactly analogous to that of the hCG beta core fragment. The finding of a discrete hLH beta core fragment in a tissue extract suggests that it may be produced within pituitary tissue, rather than by a peripheral degradation process. We have also found that the same immunoaffinity method used to extract the hLH beta core fragment from the pituitary extract purified several protein fragments from postmenopausal urine, none of which was related to hLH or hCG. The availability of the pituitary hLH beta core fragment may allow development of assays that distinguish it from its hCG analog.