166
R. LALLIER
seems weakest during the period of determination, that is, when the
sensitivity of the egg to the animalizing action of iodosobenzoic acid is
strongest. The participation of the hexosemonophosphate shunt in the
processes of determination, and, in particular, animalization, has been
suggested by Hultin (1953e). Iodosobenzoic acid induces animalization
in sea urchin larvae (Runnström and Kriszat, 1952). According to
Hultin, iodosobenzoic acid, a SH-reagent, blocks the glycolytic cycle,
resulting in stimulation of the activity of the hexosemonophosphate
shunt. In order to test Hultin's hypothesis, Bäckström (1959b) and
Bäckström et al. (1960) have studied the activity of the hexosemonophosphate shunt in embryos animalized by iodosobenzoic acid. Two
methods have been used. The first one is based on measurement of the
activity of glucose-6-phosphate dehydrogenase, an important enzyme in
the shunt which is responsible for the oxidation of glucose-6-phosphate
to phosphogluconate. The second one is based on the conversion of the
labelled carbon of glucose- 114
C, glucose-214
C and glucose-614
C into
radioactive
1 4
C0 2 . During the utilization of the glucose by the hexosemonophosphate shunt, only the glucose-114
C contributes to the
formation of radioactive C0 2 . Bäckström (1959b) has observed that
before hatching, that is during the period of determination, the activity
of the glucose-6-phosphate dehydrogenase evolves according to a similar
pattern in the normal larvae and in the animalized larvae. After
hatching, animalized larvae have a higher enzyme level than normal
larvae. The results obtained by means of labelled glucose show that the
activity of the shunt decreases less quickly in animalized blastulae than
in controls (Bäckström et al., 1960). It appears then that the embryos
animalized by iodosobenzoic acid have a very active hexosemonophosphate shunt. The animalizing effects of phosphogluconic acid, a
shunt metabolite, and the vegetalizing effects of shunt inhibitors such as
dinitrocresol and dinitrophenol support Hultin's suggestion that the
hexosemonophosphate shunt may be important in the determination of
animal structures. We must, however, point out that bromoacetate and
iodoacetate, which block glycolysis while leaving a residual respiration
corresponding to the activity of the shunt (Lipmann, 1936 ; Barker et al.,
1939), are not animalizing. Another inhibitor of glycolysis, 2-deoxyglucose, prevents the formation of fructose-6-phosphate from the
glucose-6-phosphate (Sols and Crane, 1954). In these conditions, it may
be conceived that the glucose-6-phosphate is degraded preferentially by
the pathway of the hexosemonophosphate shunt. 2-Deoxyglucose does
not exert animalizing effects (Lallier, 1960c). If the effects on development of various shunt inhibitors, such as p-chloromercuribenzoic acid
and iV-ethylmaleimide, which inhibit characteristic reactions of the
hexosemonophosphate shunt (Tabachnick et al., 1958), are examined, it
R. LALLIER
seems weakest during the period of determination, that is, when the
sensitivity of the egg to the animalizing action of iodosobenzoic acid is
strongest. The participation of the hexosemonophosphate shunt in the
processes of determination, and, in particular, animalization, has been
suggested by Hultin (1953e). Iodosobenzoic acid induces animalization
in sea urchin larvae (Runnström and Kriszat, 1952). According to
Hultin, iodosobenzoic acid, a SH-reagent, blocks the glycolytic cycle,
resulting in stimulation of the activity of the hexosemonophosphate
shunt. In order to test Hultin's hypothesis, Bäckström (1959b) and
Bäckström et al. (1960) have studied the activity of the hexosemonophosphate shunt in embryos animalized by iodosobenzoic acid. Two
methods have been used. The first one is based on measurement of the
activity of glucose-6-phosphate dehydrogenase, an important enzyme in
the shunt which is responsible for the oxidation of glucose-6-phosphate
to phosphogluconate. The second one is based on the conversion of the
labelled carbon of glucose- 114
C, glucose-214
C and glucose-614
C into
radioactive
1 4
C0 2 . During the utilization of the glucose by the hexosemonophosphate shunt, only the glucose-114
C contributes to the
formation of radioactive C0 2 . Bäckström (1959b) has observed that
before hatching, that is during the period of determination, the activity
of the glucose-6-phosphate dehydrogenase evolves according to a similar
pattern in the normal larvae and in the animalized larvae. After
hatching, animalized larvae have a higher enzyme level than normal
larvae. The results obtained by means of labelled glucose show that the
activity of the shunt decreases less quickly in animalized blastulae than
in controls (Bäckström et al., 1960). It appears then that the embryos
animalized by iodosobenzoic acid have a very active hexosemonophosphate shunt. The animalizing effects of phosphogluconic acid, a
shunt metabolite, and the vegetalizing effects of shunt inhibitors such as
dinitrocresol and dinitrophenol support Hultin's suggestion that the
hexosemonophosphate shunt may be important in the determination of
animal structures. We must, however, point out that bromoacetate and
iodoacetate, which block glycolysis while leaving a residual respiration
corresponding to the activity of the shunt (Lipmann, 1936 ; Barker et al.,
1939), are not animalizing. Another inhibitor of glycolysis, 2-deoxyglucose, prevents the formation of fructose-6-phosphate from the
glucose-6-phosphate (Sols and Crane, 1954). In these conditions, it may
be conceived that the glucose-6-phosphate is degraded preferentially by
the pathway of the hexosemonophosphate shunt. 2-Deoxyglucose does
not exert animalizing effects (Lallier, 1960c). If the effects on development of various shunt inhibitors, such as p-chloromercuribenzoic acid
and iV-ethylmaleimide, which inhibit characteristic reactions of the
hexosemonophosphate shunt (Tabachnick et al., 1958), are examined, it