ANIMALIZATION AND VEGETALIZATION
173
whole eggs in the presence of lithium (Gustafson and Hörstadius, 1955).
A moderate animalizing effect has been obtained in whole eggs with
2-thio-5-methyl-cytosine, an analogue of cytosine (Gustafson and
Hörstadius, 1956). Karnofsky and Bevelander (1958) have studied the
effects of DON (6-diazo-5-oxo-L-norleucine) and azaserine (O-diazoacetyl-L-serine) on the development of sand-dollar embryos. These
glutamine antagonists interfere with the synthesis of purines. They
interrupt the development of embryos at the mid-blastula and early
gastrula stages. 5-Pluorodeoxyuridine and related halogenated pyrimidines, which specifically interfere with pyrimidine metabolism, block
development at the early blastula stage (Karnofsky and Bäsch, 1960).
Lallier (1962c) has observed the inhibition of development of eggs by
various analogues of purines and pyrimidines, such as 6-mercaptopurine,
benzimidazole, 6-azauridine, 2-thiouracil and 5-azathymine. A few
radialized larvae are obtained with 6-azauracil and 8-azaguanine. The
radializing effect of these analogues are not reversed by the natural
metabolite. Further, of several analogues of uracil, only 6-azauracil
exerts radializing effects. These results suggest that the radializing effect
of these two analogues is not connected with their antimetabolic
properties.
In conclusion, it may be seen that the changes in the determination
induced by antimetabolites of purines and pyrimidines are weak and
frequently lacking in consistency. The irregularities observed in the
action of some antimetabolites raise doubt about the idea that they act
by virtue of their antimetabolite properties. Thus the analogues may
act by virtue of other properties such as surface activity or chelating
activity. Antimetabolite activity may be verified by studying the
simultaneous effects of the antimetabolite and of the corresponding
normal metabolite. In the event of a purely antimetabolic action of the
analogue, its action could then be either suppressed or reduced in the
presence of the normal metabolite.
VIII. Enzymes, Mitochondria and Embryonic Development
The activity of a great number of enzymes has been measured in
normal embryos and in embryos vegetalized by lithium ions (Gustafson
and Hasselberg, 1951). The activity of the enzymes studied may be
classed in two groups.
The enzymes of the first group have a fairly constant activity throughout development. Lithium ions do not inhibit the activity of these
enzymes. In this group are aldolase, phenylsulphatase, a proteolytic
enzyme, pyrophosphatase, hexosemonophosphate and an acid phosphatase (Fig. 11).
173
whole eggs in the presence of lithium (Gustafson and Hörstadius, 1955).
A moderate animalizing effect has been obtained in whole eggs with
2-thio-5-methyl-cytosine, an analogue of cytosine (Gustafson and
Hörstadius, 1956). Karnofsky and Bevelander (1958) have studied the
effects of DON (6-diazo-5-oxo-L-norleucine) and azaserine (O-diazoacetyl-L-serine) on the development of sand-dollar embryos. These
glutamine antagonists interfere with the synthesis of purines. They
interrupt the development of embryos at the mid-blastula and early
gastrula stages. 5-Pluorodeoxyuridine and related halogenated pyrimidines, which specifically interfere with pyrimidine metabolism, block
development at the early blastula stage (Karnofsky and Bäsch, 1960).
Lallier (1962c) has observed the inhibition of development of eggs by
various analogues of purines and pyrimidines, such as 6-mercaptopurine,
benzimidazole, 6-azauridine, 2-thiouracil and 5-azathymine. A few
radialized larvae are obtained with 6-azauracil and 8-azaguanine. The
radializing effect of these analogues are not reversed by the natural
metabolite. Further, of several analogues of uracil, only 6-azauracil
exerts radializing effects. These results suggest that the radializing effect
of these two analogues is not connected with their antimetabolic
properties.
In conclusion, it may be seen that the changes in the determination
induced by antimetabolites of purines and pyrimidines are weak and
frequently lacking in consistency. The irregularities observed in the
action of some antimetabolites raise doubt about the idea that they act
by virtue of their antimetabolite properties. Thus the analogues may
act by virtue of other properties such as surface activity or chelating
activity. Antimetabolite activity may be verified by studying the
simultaneous effects of the antimetabolite and of the corresponding
normal metabolite. In the event of a purely antimetabolic action of the
analogue, its action could then be either suppressed or reduced in the
presence of the normal metabolite.
VIII. Enzymes, Mitochondria and Embryonic Development
The activity of a great number of enzymes has been measured in
normal embryos and in embryos vegetalized by lithium ions (Gustafson
and Hasselberg, 1951). The activity of the enzymes studied may be
classed in two groups.
The enzymes of the first group have a fairly constant activity throughout development. Lithium ions do not inhibit the activity of these
enzymes. In this group are aldolase, phenylsulphatase, a proteolytic
enzyme, pyrophosphatase, hexosemonophosphate and an acid phosphatase (Fig. 11).