On the fractionation of the proteins of egg yolk.

For many years the senior author has attempted to fractionate the yolk proteins of the Atlantic salmon with each annual laying season, but without conspicuous success. The newer electrophoretic technique has now provided us with a better criterion of the success of our methods as applied to the egg yolk of the hen as well as of the salmon (1). The general subject has been reviewed by Needham (2, 3) and by Jukes and Kay (4). Until recently the existence of three proteins had been claimed in egg yolk: (1) a lipoprotein (lipovitellin or ichthulin), (2) a pseudoglobulin (livetin or thuchtin), and (3) a mucoid (vitellomucoid). In 1946 Fevold and Lausten (5) isolated a lipoprotein from hen’s egg yolk which they named lipovitellenin. This protein differed from lipovitellin in containing a higher lipide content, 36 to 41 per cent, and in exhibiting a greater instability in contact with acetone. Mecham and Olcott (6) have isolated another phosphoprotein which they have named phosvitin. Their preparation contained 10 per cent of phosphorus and comprised 7.0 per cent of the total proteins. Shepard and Hottle (7) have attempted to purify livetin for use as an antigen. Their preparations exhibited three components on electrophoretic analysis. Although our methods have not achieved fractions of the desired degree of homogeneity, it seems useful to publish the results at the present time. The fractionation of yolk proteins into the three components, demonstrable electrophoretically, does not appear to be readily accomplished in salmon yolk as tested electrophoretically.