AMPHIBIAN AND INVERTEBRATE DEVELOPMENT 69
Wasteneys and Borsook, 1924, 1925). The hypothesis of a peptidebinding ability of intracellular proteolytic enzymes does not contradict
the theoretical principles of enzymology. As is known, one and the same
enzyme, depending on the energetic conditions of the system, can produce destructive or synthesizing effects, for enzymatic catalysis is
theoretically reversible. In addition to Danilewski's work, which is
unquestionably valuable from an experimental and historical viewpoint,
and omitting other data available in the literature and cited by us in
previous papers, we must mention the recent observations made by
Mycek and Fruton (1957) on papain as a catalyst in transamination
reactions; their positive evidence fits the original view of Fruton
(1941, 1950) that protein synthesis is conditioned by transpeptization
reactions, in which glutamine, glutathione and y-glutamylpeptide
participate.
In contradiction of this de Duve (1959), surveying the functions of
intracellular hydrolases, reached the conclusion that these enzymes
very seldom participate in synthetic or transfer reactions and that their
general role chiefly concerns hydrolytic processes. He dwells especially
on autolytic phenomena due to the liberation of enzymes localized in the
lysosomes (Brächet et ah, 1958; Brächet, 1960a): this interesting subject
warrants further research.
It has already been mentioned that in the metamorphosis of amphibians and insects, there is substantial destruction of tissues and organs
of an autolytic nature (Ägrell, 1947, 1949, 1953; Braus, 1906; Etkin,
1955; Helff, 1926, 1930, 1932; Morse, 1918; Needham, 1942; Urbani,
1957; van der Jagt, 1929). Proteolytic enzymes undoubtedly play a
primary role in these phenomena, but we are as yet unable to establish
their share of activity in the destructive and reconstructive processes
(Benz, 1957; Helff, 1926, 1932; Morse, 1918; Weber, 1957).
Significant in this respect is the increased activity of these enzymes,
and of dipeptidases, in regenerative blastema (Deuchar et ah, 1957;
Jensen et ah, 1956; Orechowitsch et ah, 1935; Urbani, 1955b; Urbani,
Bellini and Zappanico, 1958; Urbani, 1962). Sylven and co-workers
(1959), observed cyclic dipeptidase and cathepsin activity in yeast multiplication, and expressed their belief that intracellular proteases play a
definite role in the intracellular reactions in which the metabolic amino
acid pool necessary for protein synthesis is replenished.
On the basis of published data, the only statement that can be made
at the moment is that intracellular proteolytic enzymes definitely participate in protein metabolism, and presumably participate in the mobilization of yolk proteins during ontogenesis to build up the new organism.
The results of our studies on dipeptidases, tripeptidases and proteinases
in the embryonic development of both vertebrates and invertebrates
Wasteneys and Borsook, 1924, 1925). The hypothesis of a peptidebinding ability of intracellular proteolytic enzymes does not contradict
the theoretical principles of enzymology. As is known, one and the same
enzyme, depending on the energetic conditions of the system, can produce destructive or synthesizing effects, for enzymatic catalysis is
theoretically reversible. In addition to Danilewski's work, which is
unquestionably valuable from an experimental and historical viewpoint,
and omitting other data available in the literature and cited by us in
previous papers, we must mention the recent observations made by
Mycek and Fruton (1957) on papain as a catalyst in transamination
reactions; their positive evidence fits the original view of Fruton
(1941, 1950) that protein synthesis is conditioned by transpeptization
reactions, in which glutamine, glutathione and y-glutamylpeptide
participate.
In contradiction of this de Duve (1959), surveying the functions of
intracellular hydrolases, reached the conclusion that these enzymes
very seldom participate in synthetic or transfer reactions and that their
general role chiefly concerns hydrolytic processes. He dwells especially
on autolytic phenomena due to the liberation of enzymes localized in the
lysosomes (Brächet et ah, 1958; Brächet, 1960a): this interesting subject
warrants further research.
It has already been mentioned that in the metamorphosis of amphibians and insects, there is substantial destruction of tissues and organs
of an autolytic nature (Ägrell, 1947, 1949, 1953; Braus, 1906; Etkin,
1955; Helff, 1926, 1930, 1932; Morse, 1918; Needham, 1942; Urbani,
1957; van der Jagt, 1929). Proteolytic enzymes undoubtedly play a
primary role in these phenomena, but we are as yet unable to establish
their share of activity in the destructive and reconstructive processes
(Benz, 1957; Helff, 1926, 1932; Morse, 1918; Weber, 1957).
Significant in this respect is the increased activity of these enzymes,
and of dipeptidases, in regenerative blastema (Deuchar et ah, 1957;
Jensen et ah, 1956; Orechowitsch et ah, 1935; Urbani, 1955b; Urbani,
Bellini and Zappanico, 1958; Urbani, 1962). Sylven and co-workers
(1959), observed cyclic dipeptidase and cathepsin activity in yeast multiplication, and expressed their belief that intracellular proteases play a
definite role in the intracellular reactions in which the metabolic amino
acid pool necessary for protein synthesis is replenished.
On the basis of published data, the only statement that can be made
at the moment is that intracellular proteolytic enzymes definitely participate in protein metabolism, and presumably participate in the mobilization of yolk proteins during ontogenesis to build up the new organism.
The results of our studies on dipeptidases, tripeptidases and proteinases
in the embryonic development of both vertebrates and invertebrates