Metabolism of ovomucoid by the developing chick embryo

A glycoprotein resembling ovomucoid was purified from chorioallantoic membranes of 12.5 day chick embryos by a sequential procedure involving zinc chloride precipitation, hydroxylapatite chromatography, and ion exchange chromatography on DEAE‐ and CM‐cellulose. The resulting preparation was homogeneous as indicated by polyacrylamide gel electrophoresis at 3 pH values, isoelectric focusing, ultracentrifugation, and immunochemical analysis. The purified material had an isoelectric point of 4.8, molecular weight of 29,500 and contained 1.6 moles of galactose, 7.7 moles of mannose, 22.8 moles of N ‐acetylglucosamine and 0.4 mole of glucose per mole of protein. The ovomucoid fraction inhibited bovine trypsin, forming a 1 to 1 complex on a molar basis, and elicited a positive anaphylactoid response in albino rats at levels as low as 0.5 μg. A specific ovomucoid antiserum was obtained from rabbits that allowed investigation of the mobilization and metabolism of ovomucoid in the developing chick embryo. These studies revealed that between days 12 and 13 of embryo development a progressive migration of ovomucoid occurs from the albumin sac to the amnionic sac. The glycoprotein is then swallowed and transported through the gut to the yolk sac, where it is catabolized by proteases and glycosidases contained in the yolk sac membrane. Between day 12 of embryo development and day 7 after hatching, ovomucoid appeared in the serum of the chick and reached a maximum value of 2.4 mg % on day 18 of embryo development.