570
ETIENNE WOLFF
inhibition is overcome and the reaction becomes reversible. Similarly,
hydrogen peroxide blocks the differentiation of somites. Cysteine
removes this inhibition too, and development starts up again.
These facts appear to support the idea of a reducing action by the
SH groups of cysteine. But, after treatment with either mercuric
chloride or hydrogen peroxide, the dialysate of egg-white is capable of
overcoming the inhibitory effect of these substances even though it does
not contain any SH groups. The author concluded from these results
that cysteine must have a specific action other than its reducing
activity and that such an action must be incorporated in cellular proteins where there may exist sulphur compounds (perhaps as disulphide)
in combinations still unknown.
4. Metabolic Activity Observed with the Aid of Isotopes
Research done by Herrmann and his colleagues by the method of
labelled markers has thrown light on the intensity of certain metabolic
processes in blastoderms explanted in vitro.
Thus, it was found that the incorporation of
1 4
C glycine into proteins
varies from organ to organ in an embryo of eleven to thirteen somites
explanted for 4 h. Maximum activity occurs at the level ofthe primitive
node and decreases as follows: primitive node (7-02*), neural tube
(6-2), somites (4-99), lateral plates (4-14), brain (3-62), heart (1-97),
notochord (1 • 18) (Schultz and Herrmann, 1958).
On the other hand, it was noted that a whole embryo of four to
seven somites, explanted for 8 h in the presence of labelled glycine, did
not significantly increase its total quantity of protein glycine, whereas
a considerable accumulation of labelled glycine did occur in the pool
of free amino acids; after 1 h, the level of
1 4
C glycine rose to 51-71
(^g x 10
3 ), and after 8 h to 314-93, whereas the level of protein glycine
remained constant around the 4 ^ g x l O
3 mark. The incorporation of
labelled glycine was weaker after the stage of eleven somites (Herrmann
and Schultz, 1958).
Under different conditions of explantation (blastoderms with or
without extra-embryonic area; in natural or synthetic media) it was
noted that the intensity of growth varied: growth was greater when the
extra-embryonic area was present and when the blastoderm was
cultivated in natural medium. According to whether its growth was
slow or rapid the blastoderm incorporated more or less
1 4
C glycine into
its proteins. It seems as if, when growth was rapid, larger molecules
aided in the formation of proteins. These are presented to the blastoderm in the complex proteins of natural culture media and not in
simple peptides like glycine. In cases where growth is either slow or
*The ratio of labelled protein glycine to total protein glycine X 10
3
.
ETIENNE WOLFF
inhibition is overcome and the reaction becomes reversible. Similarly,
hydrogen peroxide blocks the differentiation of somites. Cysteine
removes this inhibition too, and development starts up again.
These facts appear to support the idea of a reducing action by the
SH groups of cysteine. But, after treatment with either mercuric
chloride or hydrogen peroxide, the dialysate of egg-white is capable of
overcoming the inhibitory effect of these substances even though it does
not contain any SH groups. The author concluded from these results
that cysteine must have a specific action other than its reducing
activity and that such an action must be incorporated in cellular proteins where there may exist sulphur compounds (perhaps as disulphide)
in combinations still unknown.
4. Metabolic Activity Observed with the Aid of Isotopes
Research done by Herrmann and his colleagues by the method of
labelled markers has thrown light on the intensity of certain metabolic
processes in blastoderms explanted in vitro.
Thus, it was found that the incorporation of
1 4
C glycine into proteins
varies from organ to organ in an embryo of eleven to thirteen somites
explanted for 4 h. Maximum activity occurs at the level ofthe primitive
node and decreases as follows: primitive node (7-02*), neural tube
(6-2), somites (4-99), lateral plates (4-14), brain (3-62), heart (1-97),
notochord (1 • 18) (Schultz and Herrmann, 1958).
On the other hand, it was noted that a whole embryo of four to
seven somites, explanted for 8 h in the presence of labelled glycine, did
not significantly increase its total quantity of protein glycine, whereas
a considerable accumulation of labelled glycine did occur in the pool
of free amino acids; after 1 h, the level of
1 4
C glycine rose to 51-71
(^g x 10
3 ), and after 8 h to 314-93, whereas the level of protein glycine
remained constant around the 4 ^ g x l O
3 mark. The incorporation of
labelled glycine was weaker after the stage of eleven somites (Herrmann
and Schultz, 1958).
Under different conditions of explantation (blastoderms with or
without extra-embryonic area; in natural or synthetic media) it was
noted that the intensity of growth varied: growth was greater when the
extra-embryonic area was present and when the blastoderm was
cultivated in natural medium. According to whether its growth was
slow or rapid the blastoderm incorporated more or less
1 4
C glycine into
its proteins. It seems as if, when growth was rapid, larger molecules
aided in the formation of proteins. These are presented to the blastoderm in the complex proteins of natural culture media and not in
simple peptides like glycine. In cases where growth is either slow or
*The ratio of labelled protein glycine to total protein glycine X 10
3
.