62
ENRICO URBANI
peptidases and from the proteolytic enzymes capable of hydrolysing
proteins of high molecular weight (proteinases) in an acid or alkaline
medium. Our interest in this aspect was stimulated by the fact that proteases can be shown to behave differently from the autolytic enzymes
grouped under the general name of 'cathepsins'.
In consideration of the suggested and probable relationships between
intracellular proteolytic enzymes and protein synthesis during embryonic development, these data were integrated with an analysis of the
pentose-nucleic acids: dipeptidase activity and ribonucleic acid content
were shown to follow a similar pattern in change, a fact which was not
found to be peculiar to amphibian embryogenesis, but could be applied
generally to a number of different animals, both normally and under
experimental conditions. Our studies were extended to include several
phosphatases in relation to protein metabolism in the embryo and to
metamorphosis.
In addition to proteolytic enzymes and phosphatases, our investigations included work on lipases and amylases to determine the extent of
their activity in the most significant stages of ontogenesis.
Since the amphibian egg is to be considered as a 'closed system' from
the viewpoint of energy requirements, we felt that it would be interesting to establish, both quantitatively and qualitatively, the rate of yolk
utilization by determining total nitrogen, carbohydrate and lipid content from fertilization until early feeding of the young larva and again
during metamorphosis: at this stage, in the absence of nourishment from
the outside, the young animal once more behaves as a closed system and
draws the necessary supplies for energy and growth from its own tissues.
The utilization of proteins, carbohydrates and lipids at different stages
of the biological cycle yields interesting results when compared with
the activity of their three respective hydrolysing enzymes.
The methods applied in our research on amphibians were also used to
study the embryonic and post-embryonic development of a few invertebrates, such as Artemia salina Leach, Bombyx mori L., and Musca
domestica L. This last material was used mostly for studies on metamorphosis and for a comparison of the biochemical phenomena occurring in the metamorphosis of amphibians and insects. From this
body of research, it appears that the same enzyme at times shows a
different degree of activity in closely related species; in contrast, some
developmental stages of corresponding functional value, in animals
of different phyla, are characterized by a similar pattern of enzyme
activity.
This is a further confirmation of our view that zoologists and embryologists can derive definite value from biochemical and particularly
enzymological researches only at comparative levels, and only if their
ENRICO URBANI
peptidases and from the proteolytic enzymes capable of hydrolysing
proteins of high molecular weight (proteinases) in an acid or alkaline
medium. Our interest in this aspect was stimulated by the fact that proteases can be shown to behave differently from the autolytic enzymes
grouped under the general name of 'cathepsins'.
In consideration of the suggested and probable relationships between
intracellular proteolytic enzymes and protein synthesis during embryonic development, these data were integrated with an analysis of the
pentose-nucleic acids: dipeptidase activity and ribonucleic acid content
were shown to follow a similar pattern in change, a fact which was not
found to be peculiar to amphibian embryogenesis, but could be applied
generally to a number of different animals, both normally and under
experimental conditions. Our studies were extended to include several
phosphatases in relation to protein metabolism in the embryo and to
metamorphosis.
In addition to proteolytic enzymes and phosphatases, our investigations included work on lipases and amylases to determine the extent of
their activity in the most significant stages of ontogenesis.
Since the amphibian egg is to be considered as a 'closed system' from
the viewpoint of energy requirements, we felt that it would be interesting to establish, both quantitatively and qualitatively, the rate of yolk
utilization by determining total nitrogen, carbohydrate and lipid content from fertilization until early feeding of the young larva and again
during metamorphosis: at this stage, in the absence of nourishment from
the outside, the young animal once more behaves as a closed system and
draws the necessary supplies for energy and growth from its own tissues.
The utilization of proteins, carbohydrates and lipids at different stages
of the biological cycle yields interesting results when compared with
the activity of their three respective hydrolysing enzymes.
The methods applied in our research on amphibians were also used to
study the embryonic and post-embryonic development of a few invertebrates, such as Artemia salina Leach, Bombyx mori L., and Musca
domestica L. This last material was used mostly for studies on metamorphosis and for a comparison of the biochemical phenomena occurring in the metamorphosis of amphibians and insects. From this
body of research, it appears that the same enzyme at times shows a
different degree of activity in closely related species; in contrast, some
developmental stages of corresponding functional value, in animals
of different phyla, are characterized by a similar pattern of enzyme
activity.
This is a further confirmation of our view that zoologists and embryologists can derive definite value from biochemical and particularly
enzymological researches only at comparative levels, and only if their