CHANGES IN THE MAJOR MACROMOLECULAR FRACTIONS OF EGG YOLK DURING EMBRYOGENESIS

Abstract

Yolk from fertile eggs was separated into its three major fractions (granule, low-density, and water-soluble) after 0, 6, 12, 15, and 18 days' incubation. Qualitative and quantitative changes in whole yolk and its fractions were small during the first 12 days, but later marked changes occurred. A decrease in the proportions of granule and low-density fractions and an increase in the water-soluble fraction account for most of the overall changes in the nitrogen, phosphorus, and lipid contents of yolk. Qualitatively the lipid-rich low-density fractions showed little change. The granule fraction, however, lost phosphorus, and at least one new component was evident in both its ultracentrifugal and electrophoretic patterns. A marked increase in the amount of water-soluble material after 12 days' incubation can be attributed to the appearance of a new component having sedimentation and electrophoretic mobilities similar to those of ovalbumin.