STUDIES ON AMPHIBIAN YOLK .8. ESTROGEN-INDUCED HEPATIC SYNTHESIS OF A SERUM LIPOPHOSPHOPROTEIN AND ITS SELECTIVE UPTAKE BY OVARY AND TRANSFORMATION INTO YOLK PLATELET PROTEINS IN XENOPUS LAEVIS

14C-labeled leucine injected into Xenopus rapidly becomes incorporated into liver protein; subsequently the specific activity of serum protein rises. The extent of serum protein labeling is pronounced, particularly in estrogen-treated males and vitellogenic females; however, in the latter case, labeled protein rapidly disappears from the circulation and the specific activity of ovarian protein simultaneously rises to a plateau. Serum chromatograms demonstrate that most of the variable labeling of the serum is the function of a single serum component, designated SLPP. This component is produced by the liver as indicated by the synthetic capacity of liver slices in vitro, and the hepatic synthesis and secretion of SLPP appears to be under the control of estrogen. SLPP is taken up selectively by the maturing ovary and specifically by the vitellogenic oocyte. The latter, however, must first be activated by a hormonal factor in order to perform this task. Once incorporated into the oocyte, SLPP appears to transform into the two proteins of the crystalline yolk platelet, phosvitin and lipovitellin, and hence represents the precursor molecule for crystalline yolk. © 1969.