AMPHIBIAN AND INVERTEBRATE DEVELOPMENT 67
obtained for embryonic development and larval growth in both
amphibians and insects.
A. Proteolytic Enzymes
Proteolytic enzymes are responsible for the hydrolysis of proteins of
high and low molecular weight, as well as natural and synthetic dipeptides (Smith, E. L., 1952; Sumner and Somers, 1953). According to
their localization, they can be distinguished as extracellular, participating in the digestive phenomena of Metazoa and of carnivorous plants,
and intracellular, present in the protoplasm of animal and vegetal cells.
Intracellular proteolytic enzymes have been given the name of 'cathepsins' (Willstätter and Bamann, 1929), and they have been held responsible for autolysis of dead tissue in aseptic conditions (Looss, 1889): in
other words, they are inactive in the living cells and are set free only
after death, causing digestion of protoplasm and tissue collapse (de
Duve, 1959).
This interpretation of the autolytic mechanism definitely supersedes
the suggestion of Metchnikoff (1883) that autolysis is due to phagocytes;
however, this does not exclude intracellular proteolytic enzymes from
developing some activity during cell life.
For the purposes of our survey, proteolytic enzymes will be divided
into two categories: peptidases (dipeptidases and tripeptidases) and
proteinases, acting on proteins of high molecular weight, such as
haemoglobin, casein, gelatin, etc.
Peptidases with optimum pH values between 7 and 8 are generally
localized in the cell cytoplasm, and possibly in the microsomes (Brächet,
1947; Duspiva, 1942; Holter and Lovtrup, 1949). From observations on
enucleated Amoeba proteus, it seems that alanylglycine dipeptidase is
under nuclear control, while acid proteinase activity is independent of
the nucleus (Urbani, 1952). This applies also to alanylglycine dipeptidase in the cytoplasm of erythrocytes in vertebrates: in fact, the red
blood cells of the mammals, which lose their nuclei during differentiation,
display lower enzymatic activity (Salvidio and Urbani, 1954; Urbani,
1960).
Analyses of diploid and tetraploid biotypes of Artemia salina have
shown that the alanylglycine dipeptidase content is distinctly higher in
the tetraploid individuals (De Cesaris Coromaldi and Urbani, 1959,
1960). I t should be added that these enzymes are particularly abundant
in the tissues of organisms showing marked phenomena of morphogenesis, growth, and protein synthesis, and that their activity is
definitely higher in regenerative blastema (Needham, A. E., 1952;
Orechowitsch, 1936; Urbani, 1955b; Urbani, Bellini, and Zappanico,
1958; Urbani, 1962).
obtained for embryonic development and larval growth in both
amphibians and insects.
A. Proteolytic Enzymes
Proteolytic enzymes are responsible for the hydrolysis of proteins of
high and low molecular weight, as well as natural and synthetic dipeptides (Smith, E. L., 1952; Sumner and Somers, 1953). According to
their localization, they can be distinguished as extracellular, participating in the digestive phenomena of Metazoa and of carnivorous plants,
and intracellular, present in the protoplasm of animal and vegetal cells.
Intracellular proteolytic enzymes have been given the name of 'cathepsins' (Willstätter and Bamann, 1929), and they have been held responsible for autolysis of dead tissue in aseptic conditions (Looss, 1889): in
other words, they are inactive in the living cells and are set free only
after death, causing digestion of protoplasm and tissue collapse (de
Duve, 1959).
This interpretation of the autolytic mechanism definitely supersedes
the suggestion of Metchnikoff (1883) that autolysis is due to phagocytes;
however, this does not exclude intracellular proteolytic enzymes from
developing some activity during cell life.
For the purposes of our survey, proteolytic enzymes will be divided
into two categories: peptidases (dipeptidases and tripeptidases) and
proteinases, acting on proteins of high molecular weight, such as
haemoglobin, casein, gelatin, etc.
Peptidases with optimum pH values between 7 and 8 are generally
localized in the cell cytoplasm, and possibly in the microsomes (Brächet,
1947; Duspiva, 1942; Holter and Lovtrup, 1949). From observations on
enucleated Amoeba proteus, it seems that alanylglycine dipeptidase is
under nuclear control, while acid proteinase activity is independent of
the nucleus (Urbani, 1952). This applies also to alanylglycine dipeptidase in the cytoplasm of erythrocytes in vertebrates: in fact, the red
blood cells of the mammals, which lose their nuclei during differentiation,
display lower enzymatic activity (Salvidio and Urbani, 1954; Urbani,
1960).
Analyses of diploid and tetraploid biotypes of Artemia salina have
shown that the alanylglycine dipeptidase content is distinctly higher in
the tetraploid individuals (De Cesaris Coromaldi and Urbani, 1959,
1960). I t should be added that these enzymes are particularly abundant
in the tissues of organisms showing marked phenomena of morphogenesis, growth, and protein synthesis, and that their activity is
definitely higher in regenerative blastema (Needham, A. E., 1952;
Orechowitsch, 1936; Urbani, 1955b; Urbani, Bellini, and Zappanico,
1958; Urbani, 1962).