PROTEINS IN DEVELOPMENT
249
to an equal volume of the egg suspension.) After a period of 15 to 180
minutes the cultures were washed and put into pure sea water. The mortality was very high in all these experiments; the maximum being
found in the SCN- or IBA-treated cultures and the minimum in the Litreated embryos.
A second series of experiments showed that IBA or NaSCN added
three hours after fertilization to a culture of Li-treated embryos, decreased the percentage of vegetalized embryos.
These two kinds of experiment make clear that in the living embryo
also Li has a stabilizing effect which opposes the breakdown of protein
structure by urea, proteolytic enzymes or other animalizing substances.
On the other hand, animalizing substances reduce the resistance of protein to breakdown by urea and proteolytic enzymes.
Masui (1961) obtained comparable results explanting presumptive
ectoderm of Triturus gastrula. After a 4-hour treatment in 0-06 M-LiCl
he observed endoderm formation in 3 1 % of the explants, whereas in the
control embryos (treated with NaCl) no endoderm appeared. The
endoderm formation in Li-treated explants is reduced by increasing p H
(at p H 9-6-9-8 the endoderm appeared in 1 1 % of the explants).
H. Embryonic Proteins and the Nature of the Denaturation Induced by
Animalizing Agents
Proteins extracted from embryos are globular, fibrillar, or folded
fibrillar proteins which, when denatured, show a decrease in viscosity
like fibrillar proteins but do not show flow birefringence. Recently, a
systematic study was made in our laboratory to obtain these proteins
in a pure monodisperse state. It is possible to extract from fresh egg
yolk the globular lipovitellin (Fujii, 1960), the folded fibrillar lipovitellenin after lipid extraction (research in progress) and a fibrillar
fraction of livetin (Gorini and Lanzavecchia, 1955). The reduced viscosity (77/c) of all the folded fibrillar proteins studied increases when
the solution is diluted (Fig. 39). We assume tentatively that a swelling
and an unfolding of the molecules occur, but Öhrn (1958), studying
solutions of high polymers, suggests that this curve is related to an
adsorption of the substance on the viscosimeter walls.
In previous papers, I emphasized that denaturation of the proteins
extracted as euglobulin a + b is related to the formation of subunits.
Ranzi and Citterio (1954) reached the conclusion that animalizing substances lead to a breakdown of the protein molecules, and the formation
of subunits appears as a step in this phenomenon. Recently we made a
study of this, using the ultracentrifuge.
We extracted lipovitellin, by the method of Fujii. This protein after
purification is monodisperse in 2 M-NaCl. LiCl was added to the solution
249
to an equal volume of the egg suspension.) After a period of 15 to 180
minutes the cultures were washed and put into pure sea water. The mortality was very high in all these experiments; the maximum being
found in the SCN- or IBA-treated cultures and the minimum in the Litreated embryos.
A second series of experiments showed that IBA or NaSCN added
three hours after fertilization to a culture of Li-treated embryos, decreased the percentage of vegetalized embryos.
These two kinds of experiment make clear that in the living embryo
also Li has a stabilizing effect which opposes the breakdown of protein
structure by urea, proteolytic enzymes or other animalizing substances.
On the other hand, animalizing substances reduce the resistance of protein to breakdown by urea and proteolytic enzymes.
Masui (1961) obtained comparable results explanting presumptive
ectoderm of Triturus gastrula. After a 4-hour treatment in 0-06 M-LiCl
he observed endoderm formation in 3 1 % of the explants, whereas in the
control embryos (treated with NaCl) no endoderm appeared. The
endoderm formation in Li-treated explants is reduced by increasing p H
(at p H 9-6-9-8 the endoderm appeared in 1 1 % of the explants).
H. Embryonic Proteins and the Nature of the Denaturation Induced by
Animalizing Agents
Proteins extracted from embryos are globular, fibrillar, or folded
fibrillar proteins which, when denatured, show a decrease in viscosity
like fibrillar proteins but do not show flow birefringence. Recently, a
systematic study was made in our laboratory to obtain these proteins
in a pure monodisperse state. It is possible to extract from fresh egg
yolk the globular lipovitellin (Fujii, 1960), the folded fibrillar lipovitellenin after lipid extraction (research in progress) and a fibrillar
fraction of livetin (Gorini and Lanzavecchia, 1955). The reduced viscosity (77/c) of all the folded fibrillar proteins studied increases when
the solution is diluted (Fig. 39). We assume tentatively that a swelling
and an unfolding of the molecules occur, but Öhrn (1958), studying
solutions of high polymers, suggests that this curve is related to an
adsorption of the substance on the viscosimeter walls.
In previous papers, I emphasized that denaturation of the proteins
extracted as euglobulin a + b is related to the formation of subunits.
Ranzi and Citterio (1954) reached the conclusion that animalizing substances lead to a breakdown of the protein molecules, and the formation
of subunits appears as a step in this phenomenon. Recently we made a
study of this, using the ultracentrifuge.
We extracted lipovitellin, by the method of Fujii. This protein after
purification is monodisperse in 2 M-NaCl. LiCl was added to the solution