AN OOCYTIC MEMBRANE-RECEPTOR FOR BIOTIN-BINDING PROTEIN

The chicken oocyte accumulates a biotin-binding protein (BBP) in the y olk that is distinct from the avidin in the 'egg white', An identical BBP to that of yolk is also present in the circulation of the laying h en, We report the first evidence for the existence of a BBP receptor i n the oocyte vitelline membrane, Reduction of the 100 kDa receptor res ults in loss of BBP-binding activity; this suggests that a disulfide-b onded region of the receptor is necessary for maintaining BBP-binding activity, We show further that the levels of serum BBP are strictly de pendent on the presence of estrogen, As expected, BBP is not detected in significant quantities in rooster serum, Thus, these results sugges t that circulatory BBP, like other estrogen-dependent components of se rum, has a cognate binding activity on the oocyte membrane that may me diate its endocytosis.