98
ENRICO URBANI
showed that the same enzyme can vary in activity in the embryonic
phase of different Anura.
In this connection, reference should be made to the work of Boell
(1945). This author found that cytochrome oxidase activity in the embryo of Ambystoma punctatum increases in parallel with the respiratory
rate. On the contrary, Spiegelman and Steinbach (1945) observed that
the embryo of Rana pipiens, as the respiratory rate increases, cytochrome oxidase activity remains constant. Reference should also be made
to the work of L0vtrup (1955) and De Cesaris Coromaldi (1957) on the
variation in activity of tripeptidases at the same developmental stages
of different Anura and Urodeles.
These studies, when extended to the invertebrates Artemia salina and
Bombyx mori, gave some evidence of metabolic convergence. For instance, during developmental stages of the same functional value (e.g.
at the end of yolk resorption) given enzymes show an identical pattern
of activity. Proteolytic enzymes show similar activity in Ilyanassa
obsoleta and Nassarius festivus (Collier, 1957a, b), as they do during the
development of the species mentioned in this chapter; their activity
decreases at the end of embryogenesis in relation to the exhaustion of
deutoplasm.
The comparison between enzymatic activities in vertebrates and
invertebrates is therefore quite helpful in determining through metabolic behaviour, morphological and functional stages.
The role of proteolytic enzymes during embryonic and larval development has already been discussed at length. In closing, however, we must
stress that they are mostly active during the period of greatest growth,
i.e. during transformation of yolk proteins into cellular proteins. It is
therefore reasonable to assume that their activity is closely linked with
the release of the amino acids necessary to build up the new protein
molecules. This hypothesis is substantiated by the fact that, while the
activity of the other hydrolases is associated with a gradual disappearance of carbohydrates and lipids, the total nitrogen content decreases
only slightly. This indicates a close correlation between the rate of
utilization of the energy sources during development and metamorphosis and our enzymological problems. Our attention is also drawn to
the amino acids released at the various stages of development: an intensive mobilization of these compounds is actually observed just at the
time when protease activity is at a peak.
This applies also to amphibians and insects during metamorphosis,
as shown by our results.
The well-known question of 'preformation' or 'epigenesis' arises in
trying to solve the problem of the origin of the enzymes. It is still to be
proved whether the egg contains all the necessary enzymes or whether
ENRICO URBANI
showed that the same enzyme can vary in activity in the embryonic
phase of different Anura.
In this connection, reference should be made to the work of Boell
(1945). This author found that cytochrome oxidase activity in the embryo of Ambystoma punctatum increases in parallel with the respiratory
rate. On the contrary, Spiegelman and Steinbach (1945) observed that
the embryo of Rana pipiens, as the respiratory rate increases, cytochrome oxidase activity remains constant. Reference should also be made
to the work of L0vtrup (1955) and De Cesaris Coromaldi (1957) on the
variation in activity of tripeptidases at the same developmental stages
of different Anura and Urodeles.
These studies, when extended to the invertebrates Artemia salina and
Bombyx mori, gave some evidence of metabolic convergence. For instance, during developmental stages of the same functional value (e.g.
at the end of yolk resorption) given enzymes show an identical pattern
of activity. Proteolytic enzymes show similar activity in Ilyanassa
obsoleta and Nassarius festivus (Collier, 1957a, b), as they do during the
development of the species mentioned in this chapter; their activity
decreases at the end of embryogenesis in relation to the exhaustion of
deutoplasm.
The comparison between enzymatic activities in vertebrates and
invertebrates is therefore quite helpful in determining through metabolic behaviour, morphological and functional stages.
The role of proteolytic enzymes during embryonic and larval development has already been discussed at length. In closing, however, we must
stress that they are mostly active during the period of greatest growth,
i.e. during transformation of yolk proteins into cellular proteins. It is
therefore reasonable to assume that their activity is closely linked with
the release of the amino acids necessary to build up the new protein
molecules. This hypothesis is substantiated by the fact that, while the
activity of the other hydrolases is associated with a gradual disappearance of carbohydrates and lipids, the total nitrogen content decreases
only slightly. This indicates a close correlation between the rate of
utilization of the energy sources during development and metamorphosis and our enzymological problems. Our attention is also drawn to
the amino acids released at the various stages of development: an intensive mobilization of these compounds is actually observed just at the
time when protease activity is at a peak.
This applies also to amphibians and insects during metamorphosis,
as shown by our results.
The well-known question of 'preformation' or 'epigenesis' arises in
trying to solve the problem of the origin of the enzymes. It is still to be
proved whether the egg contains all the necessary enzymes or whether