ANIMALIZATION AND VEGETALIZATION
181
controls. This decrease specially affects the soluble —SH groups, chiefly
glutathione. A histochemical study of the distribution of—SH groups in
the normal embryos, or in embryos animalized by iodosobenzoic acid
did not show any gradient of distribution. Fenaux (1961) has studied
the distribution of the —SH groups by Bennett's histochemical method.
The —SH groups are distributed in an homogenous way in the gastrula
as well as in embryos animalized by zinc or vegetalized by lithium. No
gradient was observed. The embryos animalized by zinc ions stain more
strongly with Bennett's reagent than do the controls. This observation
is in good agreement with the observations of Bäckström concerning the
somewhat higher —SH content in larvae animalized by iodosobenzoic
acid. A higher —SH content after hatching seems to be connected with
animalization whatever animalizing agents are used.
The animalizing effects of several —SH blocking agents and of the
—SH compounds raises the problem of the relationship between embryonic determination and the —SH groups.
Iodosobenzoic acid animalizes whole eggs (Runnström and Kriszat,
1952). This acid is known to be an agent which oxidizes the —SH groups.
It does not appear to react to any significant extent with groups other
than —SH in proteins (Chinard and Hellerman, 1954). From the results
of Bäckström (1959a) in the larvae animalized by iodosobenzoic acid,
—SH oxidation, if it occurs, appears limited to a few groups at the
surface of the cells. Finally iodobenzoic acid formed by the reduction
of iodosobenzoic acid, and devoid of the oxidizing properties of this last,
is not animalizing (Lallier, unpublished observations). The effects of
several other agents able to oxidize or to block —SH groups have been
studied. Periodate, iodateandferricyanide, oxidize —SH groups, though
they are relatively non-specific in this. They do not exert animalizing
effects (Lallier, 1960a). Persulphate oxidizes —SH groups very slowly.
It strongly animalizes whole eggs (Lallier, 1956a). Persulphate has some
lyotropic properties like other animalizing agents, for example thiocyanate and Perchlorate (Lallier, 1957c). The activity of persulphate
seems to be related more to its lyotropic properties than to the oxidation
of —SH groups. The blocking of —SH groups may also be obtained by
means of alkylating agents such as iodoacetate. The specificity of this
reagent for —SH groups is doubtful. Iodoacetate has no animalizing
effects (Runnström, 1935b; Needham and Needham, 1940). iV-Ethylmaleimide reacts with —SH groups (Friedmann et al., 1949) but it does
not provoke animalization (Lallier, unpublished observations). Mercaptide-forming agents react with —SH groups. Only 1 mole of —SH
reacts per mole of mercury derivative, in contrast to the situation with
certain oxidizing agents which necessitate two nearby —SH groups to
allow the formation of an —S—S—bridge. This structural condition,
181
controls. This decrease specially affects the soluble —SH groups, chiefly
glutathione. A histochemical study of the distribution of—SH groups in
the normal embryos, or in embryos animalized by iodosobenzoic acid
did not show any gradient of distribution. Fenaux (1961) has studied
the distribution of the —SH groups by Bennett's histochemical method.
The —SH groups are distributed in an homogenous way in the gastrula
as well as in embryos animalized by zinc or vegetalized by lithium. No
gradient was observed. The embryos animalized by zinc ions stain more
strongly with Bennett's reagent than do the controls. This observation
is in good agreement with the observations of Bäckström concerning the
somewhat higher —SH content in larvae animalized by iodosobenzoic
acid. A higher —SH content after hatching seems to be connected with
animalization whatever animalizing agents are used.
The animalizing effects of several —SH blocking agents and of the
—SH compounds raises the problem of the relationship between embryonic determination and the —SH groups.
Iodosobenzoic acid animalizes whole eggs (Runnström and Kriszat,
1952). This acid is known to be an agent which oxidizes the —SH groups.
It does not appear to react to any significant extent with groups other
than —SH in proteins (Chinard and Hellerman, 1954). From the results
of Bäckström (1959a) in the larvae animalized by iodosobenzoic acid,
—SH oxidation, if it occurs, appears limited to a few groups at the
surface of the cells. Finally iodobenzoic acid formed by the reduction
of iodosobenzoic acid, and devoid of the oxidizing properties of this last,
is not animalizing (Lallier, unpublished observations). The effects of
several other agents able to oxidize or to block —SH groups have been
studied. Periodate, iodateandferricyanide, oxidize —SH groups, though
they are relatively non-specific in this. They do not exert animalizing
effects (Lallier, 1960a). Persulphate oxidizes —SH groups very slowly.
It strongly animalizes whole eggs (Lallier, 1956a). Persulphate has some
lyotropic properties like other animalizing agents, for example thiocyanate and Perchlorate (Lallier, 1957c). The activity of persulphate
seems to be related more to its lyotropic properties than to the oxidation
of —SH groups. The blocking of —SH groups may also be obtained by
means of alkylating agents such as iodoacetate. The specificity of this
reagent for —SH groups is doubtful. Iodoacetate has no animalizing
effects (Runnström, 1935b; Needham and Needham, 1940). iV-Ethylmaleimide reacts with —SH groups (Friedmann et al., 1949) but it does
not provoke animalization (Lallier, unpublished observations). Mercaptide-forming agents react with —SH groups. Only 1 mole of —SH
reacts per mole of mercury derivative, in contrast to the situation with
certain oxidizing agents which necessitate two nearby —SH groups to
allow the formation of an —S—S—bridge. This structural condition,