Changes in the Phosphoproteins of the Yolk During the Development of the Chick Embryo

INTRODUCTION INVESTIGATIONS on the yolk proteins of the developing chick embryo comparable to the published work on fresh yolk proteins of nonfertile eggs are not available. Although the changes in the nitrogen, phosphorus, lipid carbohydrate, and amino acid contents of the yolk during embryonic development have been reported (Needham, 1942, 1954; Romanoff and Romanoff, 1949; Williams et al., 1954), only a few scattered reports concerning any variations of definite proteins in the embryonic yolk have been cited and Schenck (1932), and later Needham (1954) in reviewing the situation considered these few scattered reports to be inconclusive. In the subsequent discussion the changes occurring in the electrophoretic components of the yolk during the incubation period are reported. METHODS Fertile eggs used in this investigation were obtained from hens fed 0.2 mc. of P32 per day, for six days before the eggs were collected for incubation. The fertile eggs were subsequently incubated . . .