286
JOHN RUNNSTRÖM
than COO~ groups to form hydrogen bonds with NH 2 groups. It is
obvious that the properties of this model are in keeping with many
results obtained in artificial activation of the sea urchin or starfish eggs,
for example, the activating effect of increased salinity. Sasaki and
Nogucki {loc. cit.) only used NaCl in their experiments; Ca
2+ may have
a stronger effect than Na
+ (see further below, Section III). The I0 4 " may
act by breaking up certain critical α-glycol groups and thus bring down
the molecular weight of a "natural" inhibitor that has the character
of a sulfated mucopolysaccharide. According to the model this decrease
in molecular weight would decrease the precipitation of the complex
between fibrinogen and sulfated polysaccharides. The conditions within
the natural complex in the egg must be more complicated than in the
model. The split processes may not involve a total separation of proteins
from an acid polysaccharide but release of a special protein of enzymatic
nature from a mucopolysaccharide. A complex between natural inhibitor
and protein may, for example, be present in the surface of the cytoplasmic membrane. It may be responsible for the intimate attachment
of the vitelline membrane to the egg surface but must be present also
below this membrane. The hydrogen bonds that must be broken up to
separate the vitelline membrane from the egg surface are perhaps mainly
the bonds between sulfate and amino groups.
The model is strictly valid only if the egg proteins involved behave
like fibrinogen. According to Partridge (1948), sulfated polysaccharides
form soluble complexes with albumin, even on the alkaline side of the
isoelectric point of this protein. Wicklund (1954b) found that addition
of albumin to the medium changed the egg so that an elevation of the
vitelline membrane easily occurred when the eggs were exposed to a
hypertonic solution. The presence of albumin also increased the rate of
fertilization (Hagström and Hagström, 1954). As mentioned previously,
treatment with periodate may bring about a preactivation, i.e., the
membrane elevation is facilitated when the egg becomes fertilized (see
Fig. 26). Preactivation means probably that the natural inhibitor has
been affected outside the cytoplasmic membrane. Only upon more prolonged treatment or increased concentration do the eggs become activated
by periodate. This may mean that the reagent has penetrated through
the plasma membrane and acted upon the natural inhibitor below this
membrane so that an opening of the cortical particles ensues. Albumin
is able to facilitate the elevation of the vitelline membrane by combining
with sulfated polysaccharides but is not able to activate it. The albumin
molecule does not seem to penetrate through the plasma membrane. Its
action is, therefore, limited to the natural inhibitor present outside the
lipid layer of the plasma membrane.
JOHN RUNNSTRÖM
than COO~ groups to form hydrogen bonds with NH 2 groups. It is
obvious that the properties of this model are in keeping with many
results obtained in artificial activation of the sea urchin or starfish eggs,
for example, the activating effect of increased salinity. Sasaki and
Nogucki {loc. cit.) only used NaCl in their experiments; Ca
2+ may have
a stronger effect than Na
+ (see further below, Section III). The I0 4 " may
act by breaking up certain critical α-glycol groups and thus bring down
the molecular weight of a "natural" inhibitor that has the character
of a sulfated mucopolysaccharide. According to the model this decrease
in molecular weight would decrease the precipitation of the complex
between fibrinogen and sulfated polysaccharides. The conditions within
the natural complex in the egg must be more complicated than in the
model. The split processes may not involve a total separation of proteins
from an acid polysaccharide but release of a special protein of enzymatic
nature from a mucopolysaccharide. A complex between natural inhibitor
and protein may, for example, be present in the surface of the cytoplasmic membrane. It may be responsible for the intimate attachment
of the vitelline membrane to the egg surface but must be present also
below this membrane. The hydrogen bonds that must be broken up to
separate the vitelline membrane from the egg surface are perhaps mainly
the bonds between sulfate and amino groups.
The model is strictly valid only if the egg proteins involved behave
like fibrinogen. According to Partridge (1948), sulfated polysaccharides
form soluble complexes with albumin, even on the alkaline side of the
isoelectric point of this protein. Wicklund (1954b) found that addition
of albumin to the medium changed the egg so that an elevation of the
vitelline membrane easily occurred when the eggs were exposed to a
hypertonic solution. The presence of albumin also increased the rate of
fertilization (Hagström and Hagström, 1954). As mentioned previously,
treatment with periodate may bring about a preactivation, i.e., the
membrane elevation is facilitated when the egg becomes fertilized (see
Fig. 26). Preactivation means probably that the natural inhibitor has
been affected outside the cytoplasmic membrane. Only upon more prolonged treatment or increased concentration do the eggs become activated
by periodate. This may mean that the reagent has penetrated through
the plasma membrane and acted upon the natural inhibitor below this
membrane so that an opening of the cortical particles ensues. Albumin
is able to facilitate the elevation of the vitelline membrane by combining
with sulfated polysaccharides but is not able to activate it. The albumin
molecule does not seem to penetrate through the plasma membrane. Its
action is, therefore, limited to the natural inhibitor present outside the
lipid layer of the plasma membrane.