100
ENRICO URBANI
connection, of de Duve's (1959) critical essay, in which a whole paragraph is devoted to the question of hydrolase activity as a possible
artifact.
The idea of a possible dependence of enzymatic activity on molecular
orientation is certainly interesting from the point of view of the problems under consideration. In fact, during embryonic development
organic materials, which in the yolk present a given molecular arrangement, are continuously converted into protoplasmic structures of
molecular arrangment, according to cell differentiation.
In the experiments of Spiegelman and Steinbach (1945) the tail bud
stage represents a critical point; this is confirmed by our data on the
activity of several hydrolases. In the specific case of oxygen uptake, our
co-worker Caglioti (1951) has shown that phenanthrenquinone stimulates oxygen consumption in the embryos of Bufo vulgaris only during
the early stages of development; it no longer produces this effect at the
tail bud stage.
Runnstrom (1930) and Korr (1937) put forward the view that the
sudden activation of the Warburg and Keilin system in the Arbacia egg
at fertilization is due to the related position of the enzyme and its substrate; a similar suggestion is made by Ballentine (1940) in respect of
the dehydrogenase activity of the Arbacia egg. An alternative explanation of the same phenomena has been presented by Maggio et al. (1960)
who found an inhibitor of cytochrome oxidase in the unfertilized sea
urchin egg. Increases in enzymatic activities might thus be due not to
actual synthesis, but to the elimination of an inhibitor.
Shen (1955), in tackling the problem of enzymatic preformation and
epigenesis, also states that the appearance of an enzyme at a given stage
of development does not necessarily imply that the formation of the
enzymatic molecule coincides with the beginning of its activity, which
perhaps became apparent through a change of state; in other words,
the enzyme may be preformed and then activated at a given developmental stage. These observations and considerations in support of
structural preformation and functional epigenesis caused by the interplay of activators or inhibitors (metal ions, orientation, water content,
etc.) do not exclude true epigenesis not only of enzymatic activity, but
also of enzymatic molecules (Spiegelman et al., 1955).
Flickinger and Nace (1952), Perlmann and Gustafson (1948), Ranzi
and co-workers (1955, 1956), Spiegel (1960) and others demonstrated
that new proteins are synthesized during embryonic development, most
of which display enzymatic activity. This means that new enzymatic
molecules can be formed at given developmental stages.
Studies on adaptive enzymes have shown that enzymes can be
formed to meet the functional requirements of the organisms. The
ENRICO URBANI
connection, of de Duve's (1959) critical essay, in which a whole paragraph is devoted to the question of hydrolase activity as a possible
artifact.
The idea of a possible dependence of enzymatic activity on molecular
orientation is certainly interesting from the point of view of the problems under consideration. In fact, during embryonic development
organic materials, which in the yolk present a given molecular arrangement, are continuously converted into protoplasmic structures of
molecular arrangment, according to cell differentiation.
In the experiments of Spiegelman and Steinbach (1945) the tail bud
stage represents a critical point; this is confirmed by our data on the
activity of several hydrolases. In the specific case of oxygen uptake, our
co-worker Caglioti (1951) has shown that phenanthrenquinone stimulates oxygen consumption in the embryos of Bufo vulgaris only during
the early stages of development; it no longer produces this effect at the
tail bud stage.
Runnstrom (1930) and Korr (1937) put forward the view that the
sudden activation of the Warburg and Keilin system in the Arbacia egg
at fertilization is due to the related position of the enzyme and its substrate; a similar suggestion is made by Ballentine (1940) in respect of
the dehydrogenase activity of the Arbacia egg. An alternative explanation of the same phenomena has been presented by Maggio et al. (1960)
who found an inhibitor of cytochrome oxidase in the unfertilized sea
urchin egg. Increases in enzymatic activities might thus be due not to
actual synthesis, but to the elimination of an inhibitor.
Shen (1955), in tackling the problem of enzymatic preformation and
epigenesis, also states that the appearance of an enzyme at a given stage
of development does not necessarily imply that the formation of the
enzymatic molecule coincides with the beginning of its activity, which
perhaps became apparent through a change of state; in other words,
the enzyme may be preformed and then activated at a given developmental stage. These observations and considerations in support of
structural preformation and functional epigenesis caused by the interplay of activators or inhibitors (metal ions, orientation, water content,
etc.) do not exclude true epigenesis not only of enzymatic activity, but
also of enzymatic molecules (Spiegelman et al., 1955).
Flickinger and Nace (1952), Perlmann and Gustafson (1948), Ranzi
and co-workers (1955, 1956), Spiegel (1960) and others demonstrated
that new proteins are synthesized during embryonic development, most
of which display enzymatic activity. This means that new enzymatic
molecules can be formed at given developmental stages.
Studies on adaptive enzymes have shown that enzymes can be
formed to meet the functional requirements of the organisms. The