182
R. LALLIER
which may play a role in the action of oxidizing agents, is not so
significant in the action of the mercaptide-forming agents such as
mercury derivatives. Two of those derivatives, p-chloromercuribenzoic
acid and phenylmercuric chloride are devoid of animalizing effects
(Lallier, 1956a, 1960a). In contrast, Salyrgan, another mercury derivative, is a very active animalizing agent (Lallier, 1960a). Its effects on
determination are characterized by a high reversibility. Like iodosobenzoic acid, stabilization of the animalizing effects is obtained when the
treatment is extended beyond the blastula stage.
Some heavy metals animalize whole eggs. This is the case with zinc
and cadmium (Lallier, 1955a). The animalizing effects of zinc ions are
remarkably strong and constant. According to Lindahl (1936), mercury
also animalizes. The animalizing activity of these metals decreases in
the following order : Zn>Cd>Hg and their affinity for the —SH groups
decreases in the opposite order: Hg>Cd>Zn. These observations do
not favour the idea of a relationship between the animalizing activity of
these metals and their affinity for the —SH groups.
Thiomalic acid (COOH—CH 2 —CH 2 SH COOH), a sulphydryl substance, is a very active animalizing agent in whole eggs (Lallier, 1952).
The oxidation of the —SH groups of thiomalic acid suppresses its
animalizing properties (Lallier, 1958a). Basing his assumption on the
similarity between the formulae of thiomalic acid and the cysteine
moiety of glutathione, Bäckström (1958a) suggested that thiomalic acid
might act as an antimetabolite of glutathione. This author in fact
showed that glutathione inhibits the animalizing effects of thiomalic
acid on the eggs of the sea urchin Psammechinus
miliaris. Opposite
results have been obtained by Lallier (1959d) with the eggs of Paracentrotus lividus. In these eggs glutathione enhances the animalizing
effects of thiomalic acid. Further, Lallier has examined the effects on
development of several analogues of glutathione : #-methylglutathione,
/S^iV-ethylsuccinimido glutathione (Kermack and Matheson, 1957), and
ophthalmic acid, an analogue of glutathione discovered by Waley (1958).
These three analogues inhibit the development of the eggs of Paracentrotus lividus, and these inhibitory effects are suppressed in the presence
of glutathione. But none of these analogues animalizes the sea urchin
egg. Finally, no antagonism can be observed between cysteine and
thiomalic acid. Indeed, cysteine is very toxic to sea urchin eggs, but its
toxicity is not reduced in the presence of thiomalic acid in a 250 times
higher concentration (Lallier, 1959d). These results are not indicative of
a competition between thiomalic acid and glutathione. No antagonism
has been observed between thiomalic acid and various substrates of
carbohydrate metabolism structurally related to thiomalic acid such as
succinic acid and malic acids (Lallier, unpublished observations).
R. LALLIER
which may play a role in the action of oxidizing agents, is not so
significant in the action of the mercaptide-forming agents such as
mercury derivatives. Two of those derivatives, p-chloromercuribenzoic
acid and phenylmercuric chloride are devoid of animalizing effects
(Lallier, 1956a, 1960a). In contrast, Salyrgan, another mercury derivative, is a very active animalizing agent (Lallier, 1960a). Its effects on
determination are characterized by a high reversibility. Like iodosobenzoic acid, stabilization of the animalizing effects is obtained when the
treatment is extended beyond the blastula stage.
Some heavy metals animalize whole eggs. This is the case with zinc
and cadmium (Lallier, 1955a). The animalizing effects of zinc ions are
remarkably strong and constant. According to Lindahl (1936), mercury
also animalizes. The animalizing activity of these metals decreases in
the following order : Zn>Cd>Hg and their affinity for the —SH groups
decreases in the opposite order: Hg>Cd>Zn. These observations do
not favour the idea of a relationship between the animalizing activity of
these metals and their affinity for the —SH groups.
Thiomalic acid (COOH—CH 2 —CH 2 SH COOH), a sulphydryl substance, is a very active animalizing agent in whole eggs (Lallier, 1952).
The oxidation of the —SH groups of thiomalic acid suppresses its
animalizing properties (Lallier, 1958a). Basing his assumption on the
similarity between the formulae of thiomalic acid and the cysteine
moiety of glutathione, Bäckström (1958a) suggested that thiomalic acid
might act as an antimetabolite of glutathione. This author in fact
showed that glutathione inhibits the animalizing effects of thiomalic
acid on the eggs of the sea urchin Psammechinus
miliaris. Opposite
results have been obtained by Lallier (1959d) with the eggs of Paracentrotus lividus. In these eggs glutathione enhances the animalizing
effects of thiomalic acid. Further, Lallier has examined the effects on
development of several analogues of glutathione : #-methylglutathione,
/S^iV-ethylsuccinimido glutathione (Kermack and Matheson, 1957), and
ophthalmic acid, an analogue of glutathione discovered by Waley (1958).
These three analogues inhibit the development of the eggs of Paracentrotus lividus, and these inhibitory effects are suppressed in the presence
of glutathione. But none of these analogues animalizes the sea urchin
egg. Finally, no antagonism can be observed between cysteine and
thiomalic acid. Indeed, cysteine is very toxic to sea urchin eggs, but its
toxicity is not reduced in the presence of thiomalic acid in a 250 times
higher concentration (Lallier, 1959d). These results are not indicative of
a competition between thiomalic acid and glutathione. No antagonism
has been observed between thiomalic acid and various substrates of
carbohydrate metabolism structurally related to thiomalic acid such as
succinic acid and malic acids (Lallier, unpublished observations).