VITELLINE MEMBRANE AND CORTICAL PARTICLES 313
of different sea urchins (Hemicentrotus,
Anthocidans,
and
Pseudocentrotus).
A fibrous precipitate was obtained by squirting out the extract into cold acetone or water. This "thread model" contracts on exposure to di- or trivalent cations; relaxation occurs when EDTA is
added. The thread model contracts also after exposure to cystine or to a
water-soluble fraction from the egg, presumably an enzyme that oxidizes
the SH groups of the thread model (Sakai, 1962b). It is remarkable that
the Ε 2 enzyme acts in a parallel way. Its activity also depends on the
oxidation-reduction state of surrounding SH compounds. A shift from
gelating to hydrolyzing activity, or from Ε 2 to Ε 1 and Ε 3 activity
(see Section II,D) occurs when S—S compounds are reduced to SH
compounds. The spontaneous shifts occurring in aged eggs or subsequent to prolongation of the treatment of the eggs with trypsin appears
in much more rapid sequence in the activation process. The contraction
of the region around the effective spermatozoon is relatively soon relaxed.
This could be ascribed to the sequential activation of the enzymes Ε 1
and Ε 3. The following conception could give a possible clue to the
mechanism of the shift. Enzyme Ε 2, like thrombin, may act by splitting
its protein substrate into a still rather large protein which gelâtes and
splits off smaller peptide fragments. These latter may be activators of
Ε 1 ; at the same time a reductase is activated which reduces S—S groups
in proteins. The increase in concentration of free SH groups activates
finally also Ε 3 (Section II,D).
It seems possible that a mechanochemical system may be operating in
the egg. Uptake or release of Ca
2+ activates the gelating enzyme Ε 2,
which is followed by an activation of an enzyme or enzyme system
oxidizing SH groups. This brings about a contraction of the threadlike
particles of Sakai (1962a). A relatively low-molecular product of the
Ε 2 activity activates the more hydrolytic enzymes Ε 1 and Ε 3. Along
with these a reductase is activated which brings about an increase in
SH groups that stop the Ε 2 activity. As a consequence, a relaxation of
the threadlike particles occurs.
T. Hultin (1949, 1950a,b) has given an important piece of evidence
for the verification of at least the first link in the suggested scheme. He
prepared homogenates of Paracentrotus
eggs in Ca-free medium. Upon
addition of Ca
2+ to these homogenates, certain components of the homogenates gelate and may be regarded as identical with Sakai's (1962a)
fibrous elements. The light scattering increases also, indicating a formation of aggregates. In addition, there is an outburst of oxygen uptake,
which depends on an oxidation of SH groups and stops when these have
been removed by the oxidation process. Moreover, Hultin found that
Ca
2+ can be replaced by papain. This tends to show that Ca
2+ acts chiefly
of different sea urchins (Hemicentrotus,
Anthocidans,
and
Pseudocentrotus).
A fibrous precipitate was obtained by squirting out the extract into cold acetone or water. This "thread model" contracts on exposure to di- or trivalent cations; relaxation occurs when EDTA is
added. The thread model contracts also after exposure to cystine or to a
water-soluble fraction from the egg, presumably an enzyme that oxidizes
the SH groups of the thread model (Sakai, 1962b). It is remarkable that
the Ε 2 enzyme acts in a parallel way. Its activity also depends on the
oxidation-reduction state of surrounding SH compounds. A shift from
gelating to hydrolyzing activity, or from Ε 2 to Ε 1 and Ε 3 activity
(see Section II,D) occurs when S—S compounds are reduced to SH
compounds. The spontaneous shifts occurring in aged eggs or subsequent to prolongation of the treatment of the eggs with trypsin appears
in much more rapid sequence in the activation process. The contraction
of the region around the effective spermatozoon is relatively soon relaxed.
This could be ascribed to the sequential activation of the enzymes Ε 1
and Ε 3. The following conception could give a possible clue to the
mechanism of the shift. Enzyme Ε 2, like thrombin, may act by splitting
its protein substrate into a still rather large protein which gelâtes and
splits off smaller peptide fragments. These latter may be activators of
Ε 1 ; at the same time a reductase is activated which reduces S—S groups
in proteins. The increase in concentration of free SH groups activates
finally also Ε 3 (Section II,D).
It seems possible that a mechanochemical system may be operating in
the egg. Uptake or release of Ca
2+ activates the gelating enzyme Ε 2,
which is followed by an activation of an enzyme or enzyme system
oxidizing SH groups. This brings about a contraction of the threadlike
particles of Sakai (1962a). A relatively low-molecular product of the
Ε 2 activity activates the more hydrolytic enzymes Ε 1 and Ε 3. Along
with these a reductase is activated which brings about an increase in
SH groups that stop the Ε 2 activity. As a consequence, a relaxation of
the threadlike particles occurs.
T. Hultin (1949, 1950a,b) has given an important piece of evidence
for the verification of at least the first link in the suggested scheme. He
prepared homogenates of Paracentrotus
eggs in Ca-free medium. Upon
addition of Ca
2+ to these homogenates, certain components of the homogenates gelate and may be regarded as identical with Sakai's (1962a)
fibrous elements. The light scattering increases also, indicating a formation of aggregates. In addition, there is an outburst of oxygen uptake,
which depends on an oxidation of SH groups and stops when these have
been removed by the oxidation process. Moreover, Hultin found that
Ca
2+ can be replaced by papain. This tends to show that Ca
2+ acts chiefly