ANIMALIZATION AND VEGETALIZATION
163
The activity of the hexosemonophosphate shunt in embryos vegetalized by lithium has been studied by Bäckström (1959b) and by
Bäckström et al. (1960). The activity of glucose-6-phosphate dehydrogenase, an important enzyme of the shunt, evolves in the same way in
the normal embryos and in vegetalized embryos before hatching, that is,
during the stage of embryonic determination. After hatching the
activity of this enzyme seems slightly diminished in the vegetalized
embryos. The activity of the shunt has also been determined by studying
the conversion in vivo of glucose labelled with
14
C in different positions
to
1 4
C0 2 . A similar pattern of glucose utilization is observed in the
vegetalized embryos and in normal embryos before hatching. However,
after hatching, the activity of the hexosemonophosphate shunt decreases
more quickly in the embryos treated with lithium than in normal
embryos. The activity of the hexosemonophosphate shunt seems then
comparable in normal embryos and in vegetalized embryos throughout
the phase of embryonic determination. It is only from the formation of
the entomesoderm and during the differentiation phase that a faster
decrease in the activity of the hexosemonophosphate shunt may be
observed in the vegetalized embryos.
Carbohydrate catabolism is closely bound to the metabolism of
phosphorus. The energy obtained during the degradation of the
glucides is used for the synthesis of adenosine triphosphate (ATP). ATP
can transfer its terminal phosphate group, rich in energy, to acceptors
and can thus participate in the synthesis of numerous substances. The
action of lithium on carbohydrate catabolism can thus have effects
either on the synthesis of ATP, or indirectly on the syntheses in which
ATP is engaged. The first indications in favour of an action of lithium on
synthesis involving ATP have been given by Lindahl and Kiessling
(1951). Indeed these authors have observed that lithium causes an
accumulation of inorganic pyrophosphate in the sea urchin egg treated
during cleavage, that is, during the period of determination. Pyrophosphate is implicated in numerous and important enzymatic reactions.
It is formed during the synthesis of acetyl CoA (Jones et al., 1953) and
during the activation of the carboxyl groups of the fatty acids and of the
amino-acids. Pyrophosphate also intervenes in the synthesis of the
nucleotide pyrophosphates (Kornberg et al., 1955). The study of these
enzymatic reactions can give useful indications as to the origin of the
pyrophosphate which is accumulated in the sea urchin eggs treated
with lithium. The formation of ATP can also be hindered by lithium.
Inhibition of the degradation of glucides already causes a decrease in
the quantity of ATP which is formed. A decoupling action of lithium
upon oxidizing phosphorylations may also be envisaged. It is interesting
to point out that Hörstadius (1953) has obtained vegetalization with
163
The activity of the hexosemonophosphate shunt in embryos vegetalized by lithium has been studied by Bäckström (1959b) and by
Bäckström et al. (1960). The activity of glucose-6-phosphate dehydrogenase, an important enzyme of the shunt, evolves in the same way in
the normal embryos and in vegetalized embryos before hatching, that is,
during the stage of embryonic determination. After hatching the
activity of this enzyme seems slightly diminished in the vegetalized
embryos. The activity of the shunt has also been determined by studying
the conversion in vivo of glucose labelled with
14
C in different positions
to
1 4
C0 2 . A similar pattern of glucose utilization is observed in the
vegetalized embryos and in normal embryos before hatching. However,
after hatching, the activity of the hexosemonophosphate shunt decreases
more quickly in the embryos treated with lithium than in normal
embryos. The activity of the hexosemonophosphate shunt seems then
comparable in normal embryos and in vegetalized embryos throughout
the phase of embryonic determination. It is only from the formation of
the entomesoderm and during the differentiation phase that a faster
decrease in the activity of the hexosemonophosphate shunt may be
observed in the vegetalized embryos.
Carbohydrate catabolism is closely bound to the metabolism of
phosphorus. The energy obtained during the degradation of the
glucides is used for the synthesis of adenosine triphosphate (ATP). ATP
can transfer its terminal phosphate group, rich in energy, to acceptors
and can thus participate in the synthesis of numerous substances. The
action of lithium on carbohydrate catabolism can thus have effects
either on the synthesis of ATP, or indirectly on the syntheses in which
ATP is engaged. The first indications in favour of an action of lithium on
synthesis involving ATP have been given by Lindahl and Kiessling
(1951). Indeed these authors have observed that lithium causes an
accumulation of inorganic pyrophosphate in the sea urchin egg treated
during cleavage, that is, during the period of determination. Pyrophosphate is implicated in numerous and important enzymatic reactions.
It is formed during the synthesis of acetyl CoA (Jones et al., 1953) and
during the activation of the carboxyl groups of the fatty acids and of the
amino-acids. Pyrophosphate also intervenes in the synthesis of the
nucleotide pyrophosphates (Kornberg et al., 1955). The study of these
enzymatic reactions can give useful indications as to the origin of the
pyrophosphate which is accumulated in the sea urchin eggs treated
with lithium. The formation of ATP can also be hindered by lithium.
Inhibition of the degradation of glucides already causes a decrease in
the quantity of ATP which is formed. A decoupling action of lithium
upon oxidizing phosphorylations may also be envisaged. It is interesting
to point out that Hörstadius (1953) has obtained vegetalization with