An oocytic membrane receptor for biotin‐binding protein

Abstract

The chicken oocyte accumulates a biotin-binding protein (BBP) in the yolk 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 hen. We report the first evidence for the existence of a BBP receptor in the oocyte vitelline membrane. Reduction of the 100 kDa receptor results in loss of BBP-binding activity; this suggests that a disulfide-bonded region of the receptor is necessary for maintaining BBP-binding activity. We show further that the levels of serum BBP are strictly dependent on the presence of estrogen. As expected, BBP is not detected in significant quantities in rooster serum. Thus, these results suggest that circulatory BBP, like other estrogen-dependent components of serum, has a cognate binding activity on the oocyte membrane that may mediate its endocytosis.

The chicken egg yolk plasma and granule proteomes

“…Yolk contained plasma retinol-binding protein, biotin-binding proteins, riboflavin-binding protein, vitamin D-binding protein, and two presumed cobalamin-binding proteins ( Table 1). Some of these proteins occur in blood and enter the oocyte by receptor-mediated endocytosis [41][42][43]. Many of these activities were identified in yolk previously and only the less well-characterized proteins will be discussed.…”