This family consists of several avian apovitellenin I sequences. As part of the avian reproductive effort, large quantities of triglyceride-rich very-low-density lipoprotein (VLDL) particles are transported by receptor-mediated endocytosis into the female germ cells. Although the oocytes are surrounded by a layer of granulosa cells harbouring high levels of active lipoprotein lipase, non-lipolysed VLDL is transported into the yolk. This is because VLDL particles from laying chickens are protected from lipolysis by apolipoprotein (apo)-VLDL-II, a potent dimeric lipoprotein lipase inhibitor [1]. Apo-VLDL-II is produced in the liver and secreted into the blood stream when induced by estrogen production in female birds.

1: Molecular characterization of quail apolipoprotein very-low-density lipoprotein II: disulphide-bond-mediated dimerization is not essential for inhibition of lipoprotein lipase. MacLachlan I, Steyrer E, Hermetter A, Nimpf J, Schneider WJ; Biochem J 1996;317:599-604. PMID:8713091