224
RUTH BELLAIRS
blood serum globulins was shown by Jukes and Kay (1932) and Jukes
et al. (1934). The transfer of serum proteins across the follicle has also
been demonstrated (see Section III, B).
Phosvitin
This contains nearly 10% phosphorus and 60-70% of the total
protein phosphorus of the yolk (Mecham and Olcott, 1949). It was formerly included in the vitellin fraction before its separate identity was
established. It has a high serine content, and according to Schjeide and
Urist (1959) binds 75% of the calcium in yolk. Schjeide andUrist (1960),
who have renamed it X x phosphoprotein, believe it to correspond with
y-livetin, though this is denied by Cook.
Phosvitin has a molecular weight of 3-0 x 10
4
at p H 4-0 and appears
to be a polyelectrolyte whose properties depend on the concentration of
both the solute and the solvent (Joubert and Cook, 1958b). According to
Sato et al. (1962) it has an anti-clotting activity in chick blood in vitro.
It has recently been split into two fractions by Connelly and Taborsky
(1961).
Phosvitin resembles other yolk proteins in that substances whose
Chromatographie patterns are identical to it have been found in the
blood serum of laying hens (Mok et al., 1961) ; i.e. the phosvitin of yolk is
the same substance as the phosvitin of the serum.
Lipovitellenin
This lipoprotein is obtained after ultracentrifugation from the
supernatant or low density fraction of the yolk (Fevold and Lausten,
1945). In the older literature it is included in the vitellin fraction. I t
contains about 38-6% of the yolk protein and 93-2% of the lipid (Evans
and Bandemer, 1961). The lipid is mainly lightly bound neutral fat
(Evans and Bandemer, 1961), about half being ether-soluble and about
half being alcohol-soluble (Neelin and Cook, 1961). According to Sato
et al. (1962) the levels of the low density proteins in the yolk, which are
essentially lipovitelleniri, are greatly influenced by the food intake of
the hen.
2. Yolk Lipids
The yolk lipids constitute about 6-1 g of the yolk (Romanoff and
Romanoff, 1949) being composed mainly of glycerides and phospholipids. Much of this lipid is bound with the egg lipo-proteins (see above).
About one-quarter of lipovitellin is lipid (Evans and Bandemer, 1961 ;
Martin et al., 1963), of which 6 1 % is phospholipid, 35% triglycéride and
4% cholesterol and its esters. The low density fraction has about 80%
of lipid, of which 27% is phospholipid, 69% triglycéride and 4%
cholesterol and its esters (Martin et al., 1963).
RUTH BELLAIRS
blood serum globulins was shown by Jukes and Kay (1932) and Jukes
et al. (1934). The transfer of serum proteins across the follicle has also
been demonstrated (see Section III, B).
Phosvitin
This contains nearly 10% phosphorus and 60-70% of the total
protein phosphorus of the yolk (Mecham and Olcott, 1949). It was formerly included in the vitellin fraction before its separate identity was
established. It has a high serine content, and according to Schjeide and
Urist (1959) binds 75% of the calcium in yolk. Schjeide andUrist (1960),
who have renamed it X x phosphoprotein, believe it to correspond with
y-livetin, though this is denied by Cook.
Phosvitin has a molecular weight of 3-0 x 10
4
at p H 4-0 and appears
to be a polyelectrolyte whose properties depend on the concentration of
both the solute and the solvent (Joubert and Cook, 1958b). According to
Sato et al. (1962) it has an anti-clotting activity in chick blood in vitro.
It has recently been split into two fractions by Connelly and Taborsky
(1961).
Phosvitin resembles other yolk proteins in that substances whose
Chromatographie patterns are identical to it have been found in the
blood serum of laying hens (Mok et al., 1961) ; i.e. the phosvitin of yolk is
the same substance as the phosvitin of the serum.
Lipovitellenin
This lipoprotein is obtained after ultracentrifugation from the
supernatant or low density fraction of the yolk (Fevold and Lausten,
1945). In the older literature it is included in the vitellin fraction. I t
contains about 38-6% of the yolk protein and 93-2% of the lipid (Evans
and Bandemer, 1961). The lipid is mainly lightly bound neutral fat
(Evans and Bandemer, 1961), about half being ether-soluble and about
half being alcohol-soluble (Neelin and Cook, 1961). According to Sato
et al. (1962) the levels of the low density proteins in the yolk, which are
essentially lipovitelleniri, are greatly influenced by the food intake of
the hen.
2. Yolk Lipids
The yolk lipids constitute about 6-1 g of the yolk (Romanoff and
Romanoff, 1949) being composed mainly of glycerides and phospholipids. Much of this lipid is bound with the egg lipo-proteins (see above).
About one-quarter of lipovitellin is lipid (Evans and Bandemer, 1961 ;
Martin et al., 1963), of which 6 1 % is phospholipid, 35% triglycéride and
4% cholesterol and its esters. The low density fraction has about 80%
of lipid, of which 27% is phospholipid, 69% triglycéride and 4%
cholesterol and its esters (Martin et al., 1963).