ANIMALIZATION AND VEGETALIZATION
183
Besides thiomalic acid, various —SH compounds have been studied.
They are glutathione, cysteine, thioglycolic and mercaptopropionic
acids, mercaptoethanol, thioglycerol, thiosorbitol, dimercaptopropanol
and j8-mercaptoethylamine. None of these substances exerts animalizing
effects (Lallier, 1958a, 1962d). Thiosorbitol and thiglycerol, like
mercaptoethanol, inhibit mitosis and disorganize the mitotic apparatus
(Mazia, 1958; Mazia and Zimmerman, 1958; Lallier, 1962a). In contrast,
thiomalic acid is devoid of antimitotic effects. This is probably due to
the lack of penetration of this agent into the eggs. This observation
suggests that the animalizing effects of thiomalic acid may result from
its action on structures localized at, or near, the cell surface.
Thus the observations made with —SH agents do not suggest a
definite conclusion concerning the role of —SH groups in the processes
of embryonic determination. The participation of —SH groups in
many cellular functions complicates the problem even more. Besides the
—S—S—bridges, the formation of hydrogen bonds between—SH and
—NH 2 groups has been postulated by a number of workers (Cecil, 1950;
Benesch and Benesch, 1953). Bârâny (1956) has suggested that some
bonds of this type play a role in the polymerization of actin. The
possibility of such bonds is interesting. Indeed, many very active
animalizing agents have an affinity for the —NH 2 groups of proteins.
They are various acidic organic compounds with sulphonic or carboxylic
groups. Their animalizing activity is a function of their affinity for
proteins (Fig. 13). It increases with the strength of their acid function
(Lallier, 1957a, b, d, 1958b). The absence of reactivity towards —SH
groups has been pointed out for one of these agents, the Suramin (Wilson
and Wormall, 1949; Wills and Wormall, 1950). Their afiinity for the
—NH 2 groups may interfere with the formation of bonds between
—NH 2 and —SH groups. According to these considerations, the high
animalizing activity of zinc ions may be explained by their double
affinity for the —SH and basic groups of proteins. Likewise, the
additivity of the animalizing effects of zinc ions and a polysulphonic
dye, Evans blue (Lallier, 1959b), may result in their fixation to —SH
and —NH 2 groups. These observations support the idea that the
inhibition of the formation of bonds between —SH and —NH 2 groups
by —SH agents and acidic organic compounds may play a role in the
process of animalization.
X. Structural Aspects of Embryonic Determination
and Differentiation
Experimental changes of embryonic determination are accompanied
by modifications in the cytological aspects of cells and in the physicochemical properties of proteins.
183
Besides thiomalic acid, various —SH compounds have been studied.
They are glutathione, cysteine, thioglycolic and mercaptopropionic
acids, mercaptoethanol, thioglycerol, thiosorbitol, dimercaptopropanol
and j8-mercaptoethylamine. None of these substances exerts animalizing
effects (Lallier, 1958a, 1962d). Thiosorbitol and thiglycerol, like
mercaptoethanol, inhibit mitosis and disorganize the mitotic apparatus
(Mazia, 1958; Mazia and Zimmerman, 1958; Lallier, 1962a). In contrast,
thiomalic acid is devoid of antimitotic effects. This is probably due to
the lack of penetration of this agent into the eggs. This observation
suggests that the animalizing effects of thiomalic acid may result from
its action on structures localized at, or near, the cell surface.
Thus the observations made with —SH agents do not suggest a
definite conclusion concerning the role of —SH groups in the processes
of embryonic determination. The participation of —SH groups in
many cellular functions complicates the problem even more. Besides the
—S—S—bridges, the formation of hydrogen bonds between—SH and
—NH 2 groups has been postulated by a number of workers (Cecil, 1950;
Benesch and Benesch, 1953). Bârâny (1956) has suggested that some
bonds of this type play a role in the polymerization of actin. The
possibility of such bonds is interesting. Indeed, many very active
animalizing agents have an affinity for the —NH 2 groups of proteins.
They are various acidic organic compounds with sulphonic or carboxylic
groups. Their animalizing activity is a function of their affinity for
proteins (Fig. 13). It increases with the strength of their acid function
(Lallier, 1957a, b, d, 1958b). The absence of reactivity towards —SH
groups has been pointed out for one of these agents, the Suramin (Wilson
and Wormall, 1949; Wills and Wormall, 1950). Their afiinity for the
—NH 2 groups may interfere with the formation of bonds between
—NH 2 and —SH groups. According to these considerations, the high
animalizing activity of zinc ions may be explained by their double
affinity for the —SH and basic groups of proteins. Likewise, the
additivity of the animalizing effects of zinc ions and a polysulphonic
dye, Evans blue (Lallier, 1959b), may result in their fixation to —SH
and —NH 2 groups. These observations support the idea that the
inhibition of the formation of bonds between —SH and —NH 2 groups
by —SH agents and acidic organic compounds may play a role in the
process of animalization.
X. Structural Aspects of Embryonic Determination
and Differentiation
Experimental changes of embryonic determination are accompanied
by modifications in the cytological aspects of cells and in the physicochemical properties of proteins.