74
E N R I C O U R B A N I
high metabolic activity, as confirmed by oxygen uptake. The activity
increases gradually during development and decreases sharply in nonfeeding larvae. In addition, they exhibit specific characteristics which
differentiate them from the previously mentioned peptidases (Urbani,
1957). Alkaline proteinase shows an almost constant degree of activity
during metamorphosis, while the activity of acid proteinase increases
markedly from the first to the fifth stage (Fig. 6). Thus at this developmental stage, as in embryogenesis, the two proteinases show a different
pattern of activity, which is proof of the different roles they are called
upon to play.
As already mentioned, tail resorption is the most striking phenomenon in the metamorphosis of the anura. Lindeman (1929) considers
that at least two factors participate in this process, one being present
in the tail itself, while the other is transported in the blood stream and
induces, at a given moment, histolysis. I t has also been suggested that
the development of the urostyle is responsible for tail necrosis and
regression (Barfurth, 1887; Helff, 1930). I t should be mentioned that
Morse (1918) was the first to demonstrate that the homogenate of a
regressive tail shows more intense proteolytic activity than the homogenate of normal tails: a finding which was later confirmed by other
authors who used different techniques and procedures (Benz, 1957;
Weber, 1957; Zacchei, 1954).
During resorption, the p H value of the caudal tissues drops from 7-5
to 6-6: this acidosis might be responsible for the activation of acid
proteinases, but not of alkaline proteinase and dipeptidase. It has been
observed that amino nitrogen released in the regressive tail tissues increases by 82%, indicating considerable protein metabolism (Needham,
1942).
These data prompted us to analyse normal and regressive tail tissues
for enzyme content; we will briefly summarize the results, referring the
reader to the original studies for the full details (Bellini, 1958; De
Cesaris Coromaldi, 1958; Urbani, 1957; Zacchei, 1954).
Dipeptidases, tripeptidases and acid and alkaline proteinases are less
active in the tail at the first stage than at the third and fourth stages.
The increase varies proportionally for the different proteolytic enzymes,
but can always be determined. Amy läse activity also increases slightly,
while lipase activity remains relatively constant. These results will be
dealt with more fully later. They confirm that intensive protein metabolism is taking place.
As already stated, Frieden and Naile (1955) recognized the important
role played by glycocorticoids in protein mobilization; thyroxin is also
markedly active in this sense (Withe, 1949). Although an apparent
correlation exists between thyroid activity and metamorphosis, it is
E N R I C O U R B A N I
high metabolic activity, as confirmed by oxygen uptake. The activity
increases gradually during development and decreases sharply in nonfeeding larvae. In addition, they exhibit specific characteristics which
differentiate them from the previously mentioned peptidases (Urbani,
1957). Alkaline proteinase shows an almost constant degree of activity
during metamorphosis, while the activity of acid proteinase increases
markedly from the first to the fifth stage (Fig. 6). Thus at this developmental stage, as in embryogenesis, the two proteinases show a different
pattern of activity, which is proof of the different roles they are called
upon to play.
As already mentioned, tail resorption is the most striking phenomenon in the metamorphosis of the anura. Lindeman (1929) considers
that at least two factors participate in this process, one being present
in the tail itself, while the other is transported in the blood stream and
induces, at a given moment, histolysis. I t has also been suggested that
the development of the urostyle is responsible for tail necrosis and
regression (Barfurth, 1887; Helff, 1930). I t should be mentioned that
Morse (1918) was the first to demonstrate that the homogenate of a
regressive tail shows more intense proteolytic activity than the homogenate of normal tails: a finding which was later confirmed by other
authors who used different techniques and procedures (Benz, 1957;
Weber, 1957; Zacchei, 1954).
During resorption, the p H value of the caudal tissues drops from 7-5
to 6-6: this acidosis might be responsible for the activation of acid
proteinases, but not of alkaline proteinase and dipeptidase. It has been
observed that amino nitrogen released in the regressive tail tissues increases by 82%, indicating considerable protein metabolism (Needham,
1942).
These data prompted us to analyse normal and regressive tail tissues
for enzyme content; we will briefly summarize the results, referring the
reader to the original studies for the full details (Bellini, 1958; De
Cesaris Coromaldi, 1958; Urbani, 1957; Zacchei, 1954).
Dipeptidases, tripeptidases and acid and alkaline proteinases are less
active in the tail at the first stage than at the third and fourth stages.
The increase varies proportionally for the different proteolytic enzymes,
but can always be determined. Amy läse activity also increases slightly,
while lipase activity remains relatively constant. These results will be
dealt with more fully later. They confirm that intensive protein metabolism is taking place.
As already stated, Frieden and Naile (1955) recognized the important
role played by glycocorticoids in protein mobilization; thyroxin is also
markedly active in this sense (Withe, 1949). Although an apparent
correlation exists between thyroid activity and metamorphosis, it is