YOLK OF THE H E N ' S EGG
223
obtained. To some extent this may be because different techniques
have been used by different workers.
Vitellin (or ovo-vitellin)
This is normally bound with lipids, thus being present in the egg as
lipo-vitellin. Lipo-vitellin constitutes about 18% of the egg yolk solids
(Alderton and Fevold, 1945). Evans and Bandemer (1961) have calculated that it contains about 47-5% of the total protein of the yolk and
about 6-8% of thelipid. I t is rich in phosphorus, some of which is present
in the vitellin itself which is a phosphoprotein, the rest being due to
phospholipids, especially lecithin and cephalin (Chargaff, 1942a, b ;
Alderton and Fevold, 1945). According to Schjeide and Urist (1961)
20% of its weight is due to phospholipids. Lipovitellin is rich in aspartic
acid, glutamic acid, leucine, arginine and serine (Bernardi and Cook,
1960b). I t also contains a certain amount of carbohydrate and Schjeide
and Urist (1959) have therefore re-named it 'X 2 lipoglycoprotein'.
Recently, lipovitellin has been shown to consist of two main components, a- and j8-lipovitellin (Bernardi and Cook, 1960a; Cook, 1961).
These authors report that the two forms are very similar, having the
same lipid content, nitrogen content, amino acid content and molecular
weight (4 x 10
5
). They differ, however, in their protein phosphorus
content, electrophoretic mobility, absorption on hydroxapatite, ultracentrifugal behaviour in alkaline media, and solubility. A detailed
comparative analysis of their properties has been made by Martin et al.
(1963). Further developments are foreshadowed by the fact that even
the a- and ß-lipovitellins have each now been dissociated into two subunits (Radomski et al., 1963). Phosphoproteins similar to vitellin have
been isolated from the blood serum of laying hens, and there is evidence
for their direct passage into the follicle (see Section III, B).
Livetin (or ovo-livetin)
The entire water-soluble fraction of the yolk has, until recently, been
known as livetin. About 0-7 g of this material is present in a yolk of
about 18-7 g wet weight (Romanoff and Romanoff, 1949), and about
one-quarter to one-third of the yolk proteins are found in this fraction.
Formerly, livetin was considered to be a single protein, but Shepard and
Hottle (1949) distinguished three main components which then became
known as a-, ß- and y-livetin (Joubert and Cook, 1958a; Cook, 1961).
Williams (1962b) showed that the water-soluble fraction contained in
addition a fourth component, transferrin. Furthermore, he identified
the a-livetin as serum albumin, the ß-livetin as a 2 -glyco-protein, and ylivetin as serum y-globulin.
The immunological relationship between yolk livetin and maternal
223
obtained. To some extent this may be because different techniques
have been used by different workers.
Vitellin (or ovo-vitellin)
This is normally bound with lipids, thus being present in the egg as
lipo-vitellin. Lipo-vitellin constitutes about 18% of the egg yolk solids
(Alderton and Fevold, 1945). Evans and Bandemer (1961) have calculated that it contains about 47-5% of the total protein of the yolk and
about 6-8% of thelipid. I t is rich in phosphorus, some of which is present
in the vitellin itself which is a phosphoprotein, the rest being due to
phospholipids, especially lecithin and cephalin (Chargaff, 1942a, b ;
Alderton and Fevold, 1945). According to Schjeide and Urist (1961)
20% of its weight is due to phospholipids. Lipovitellin is rich in aspartic
acid, glutamic acid, leucine, arginine and serine (Bernardi and Cook,
1960b). I t also contains a certain amount of carbohydrate and Schjeide
and Urist (1959) have therefore re-named it 'X 2 lipoglycoprotein'.
Recently, lipovitellin has been shown to consist of two main components, a- and j8-lipovitellin (Bernardi and Cook, 1960a; Cook, 1961).
These authors report that the two forms are very similar, having the
same lipid content, nitrogen content, amino acid content and molecular
weight (4 x 10
5
). They differ, however, in their protein phosphorus
content, electrophoretic mobility, absorption on hydroxapatite, ultracentrifugal behaviour in alkaline media, and solubility. A detailed
comparative analysis of their properties has been made by Martin et al.
(1963). Further developments are foreshadowed by the fact that even
the a- and ß-lipovitellins have each now been dissociated into two subunits (Radomski et al., 1963). Phosphoproteins similar to vitellin have
been isolated from the blood serum of laying hens, and there is evidence
for their direct passage into the follicle (see Section III, B).
Livetin (or ovo-livetin)
The entire water-soluble fraction of the yolk has, until recently, been
known as livetin. About 0-7 g of this material is present in a yolk of
about 18-7 g wet weight (Romanoff and Romanoff, 1949), and about
one-quarter to one-third of the yolk proteins are found in this fraction.
Formerly, livetin was considered to be a single protein, but Shepard and
Hottle (1949) distinguished three main components which then became
known as a-, ß- and y-livetin (Joubert and Cook, 1958a; Cook, 1961).
Williams (1962b) showed that the water-soluble fraction contained in
addition a fourth component, transferrin. Furthermore, he identified
the a-livetin as serum albumin, the ß-livetin as a 2 -glyco-protein, and ylivetin as serum y-globulin.
The immunological relationship between yolk livetin and maternal