Direct stimulation of nucleoside triphosphatase activity in bovine luteal nuclear membranes by human chorionic...

Nuclear membranes of bovine corpora lutea contain nucleoside triphosphatase (NTPase), an enzyme involved in the nucleocytoplasmic transfer of mRNA. Upon addition to nuclear membranes, hCG stimulated this enzyme, but not Mg2+-ATPase or NADH cytochrome c reductase, in a dose-, time-, and temperature-dependent manner. Heat-denatured hCG, however, had no effect on NTPase activity. hCG antisera blocked hCG's ability to stimulate the NTPase activity. While human LH also stimulated luteal nuclear membrane NTPase activity, a variety of other hormones tested, including alpha- and beta-subunits of hCG and 1 and 10 mM cAMP, had no effect on the enzyme. hCG's effect on NTPase is tissue specific in that it had no effect on liver or kidney nuclear membrane NTPase activity. In conclusion, the present data demonstrate that hCG acts directly on the luteal cell nucleus, thus raising the possibility that internalized hCG might influence nuclear functions before it is eventually degraded in lysosomes of luteal cells.