VITELLINE MEMBRANE AND CORTICAL PARTICLES 311
above for the formation and withdrawal of reception cones which represent fused villi (Section ΙΙ,Α).
Β. Mechanism and Effect of Ca
2+ Uptake
As already indicated, there is a considerable lag before the mechanism
for phosphate transport, first described by Brooks and Chambers (1948,
1954), becomes effective. The question arises as to whether some kind of
transport mechanism exists in the very first step of activation. By the
acid formation referred to above, H
+ ions are made available and tend
to diffuse into the medium; in this way a mechanism is provided for
ion exchange. Then Ca
2+ first comes into the focus of discussion. This
cation is an activator of an ATPase which seems to play a role in the
early activation process (Section II,D). Another Ca
2 +
-dependent enzyme
is the gelating enzyme corresponding to the proteolytic enzyme Ε 2,
according to the terminology of Lundblad (1954).
Heilbrunn (1937) suggested that Ca
2+ is released on fertilization from
complex binding within the cortex. According to the work of Mazia
(1937) the content of the Ca
2 +
-binding power of fertilized eggs is 15%
lower in the fertilized than in the unfertilized eggs of Arbacia
punctulata
—a result that supports Heilbrunn's suggestion. Mazia's data show that
the total calcium content is the same before and after fertilization. This
seems to indicate that an uptake of Ca
2+ from outside is not necessary.
In Mazia's experiment the eggs were frozen 5-12 min after fertilization;
at this time, changes relevant to the activation may have been already
equilibrated. Furthermore, the changes may very well lie within the errors
of the method. Evidence has been presented to show that after fertilization Ca
2+ is released from the egg so as to decrease its calcium content
(Â. Örström and M. Örström, 1942; Monroy-Oddo, 1946). Lindvall and
Carsjö (1951) found, however, that eggs deprived of their jelly coats
do not exhibit this phenomenon. Rudenberg (1953) using Ca
45 confirmed
the result of the last-mentioned authors and demonstrated that variations
in Ca
2+ content in the sea water surrounding eggs wholly depended on the
jelly coat, which according to circumstances takes up or releases Ca
2 +
.
It is known that calcium in the outer medium is necessary for a number of processes involved in the activation of the egg. After the activation the need for Ca
2+ in the medium is less pronounced. The egg in
activation cannot thus, rely on its own calcium content even if a shift
from bound to free calcium takes place. A mechanism for uptake of
Ca
2+ thus seems to be necessary for the duration of the cortical changes.
An active Ca
2+ transport has been demonstrated in rat liver mitochondria (Saris, 1963, with survey of literature). The splitting of ATP
by ATPase here gives rise to H
+ that exchanges with Ca
2 +
. A further
above for the formation and withdrawal of reception cones which represent fused villi (Section ΙΙ,Α).
Β. Mechanism and Effect of Ca
2+ Uptake
As already indicated, there is a considerable lag before the mechanism
for phosphate transport, first described by Brooks and Chambers (1948,
1954), becomes effective. The question arises as to whether some kind of
transport mechanism exists in the very first step of activation. By the
acid formation referred to above, H
+ ions are made available and tend
to diffuse into the medium; in this way a mechanism is provided for
ion exchange. Then Ca
2+ first comes into the focus of discussion. This
cation is an activator of an ATPase which seems to play a role in the
early activation process (Section II,D). Another Ca
2 +
-dependent enzyme
is the gelating enzyme corresponding to the proteolytic enzyme Ε 2,
according to the terminology of Lundblad (1954).
Heilbrunn (1937) suggested that Ca
2+ is released on fertilization from
complex binding within the cortex. According to the work of Mazia
(1937) the content of the Ca
2 +
-binding power of fertilized eggs is 15%
lower in the fertilized than in the unfertilized eggs of Arbacia
punctulata
—a result that supports Heilbrunn's suggestion. Mazia's data show that
the total calcium content is the same before and after fertilization. This
seems to indicate that an uptake of Ca
2+ from outside is not necessary.
In Mazia's experiment the eggs were frozen 5-12 min after fertilization;
at this time, changes relevant to the activation may have been already
equilibrated. Furthermore, the changes may very well lie within the errors
of the method. Evidence has been presented to show that after fertilization Ca
2+ is released from the egg so as to decrease its calcium content
(Â. Örström and M. Örström, 1942; Monroy-Oddo, 1946). Lindvall and
Carsjö (1951) found, however, that eggs deprived of their jelly coats
do not exhibit this phenomenon. Rudenberg (1953) using Ca
45 confirmed
the result of the last-mentioned authors and demonstrated that variations
in Ca
2+ content in the sea water surrounding eggs wholly depended on the
jelly coat, which according to circumstances takes up or releases Ca
2 +
.
It is known that calcium in the outer medium is necessary for a number of processes involved in the activation of the egg. After the activation the need for Ca
2+ in the medium is less pronounced. The egg in
activation cannot thus, rely on its own calcium content even if a shift
from bound to free calcium takes place. A mechanism for uptake of
Ca
2+ thus seems to be necessary for the duration of the cortical changes.
An active Ca
2+ transport has been demonstrated in rat liver mitochondria (Saris, 1963, with survey of literature). The splitting of ATP
by ATPase here gives rise to H
+ that exchanges with Ca
2 +
. A further