Studies on the Apoproteins of the Major Lipoprotein of the Yolk of Hen's Eggs I. Isolation and Properties of the Low-molecular-weight Apoproteins

Abstract

In a continuing study of protein-lipid interactions in egg yolk, the total apoprotei.n mixture (i.e. the 'apovitellenins') from the high-lipid, low-density lipoprotein (density 0·97 gJml) of the yolk from hen's eggs has been isolated in a soluble form. By gel-filtration chromatography in 6M urea the mixture has been separated into several fractions from which three new low-molecular-weight proteins (I, la, and 11), making up about 30% of the total, have been isolated. The most plentiful of these (I) consists of stable aggregates with several identical subunits each of molecular weight about 10000. This protein is analogous to the principal protein from the corresponding lipoprotein of emu's egg yolk, i.e. emu's apovitellenin I. Hen's apovitellenin I has a slightly different amino acid composition from that of the emu; notably it contains a sulphydryl group. The hen's protein also forms more stable aggregates that are dissociated by detergent and by guanidine hydrochloride but are stable in urea.