70
ENRICO URBANI
give clear evidence of a marked activity of these hydrolases during
morphogenesis and differentiation.
In closing this section on the significance of intracellular proteases, it
is important to stress, with reference to the problems under review, that
during embryonic development and metamorphosis of the amphibians,
dipeptidases and proteinases act differently from strictly autolytic enzymes (Baldisserotto and Ugurgieri, 1958; De Cesaris Coromaldi, 1959).
1. Dipeptidases and Tripeptidases
In our studies on dipeptidases, we used several substrates, such as
alanylglycine (AG), leucylglycine (LG), glycylglycine (GG), and glycylglycylglycine (GGG).
AG dipeptidase in the growing oocyte of Rana fusca and Rana
esculenta is found mainly in the cytoplasm; but some activity is shown
also in the germinal vesicle (Brächet, 1947; Duspiva, 1942).
Activity increases at fertilization: this may be due to the presence
of enzymes in the spermatozoon or to activation of preformed AG
μ\
HCI
400
200
PEPTIDASES
μ\
HCI
1400
Embryonic development
1200
1000
800
600
400
^ ^ ^
A
C
200
"
:
^=^r-*V^^^
L
9·
-
-
^ - » ·
^^letamorphosis
^ V
AC
^
^ J _ G .
Stages
B TB
300 L
hours
I
II
HI
IV
V
T
W
/TV m
Λ .
FIG. 3. Alanylglycine (AG) and leucylglycine (LG) dipeptidase in the embryonic
development and metamorphosis of Bufo vulgaris. B : blastula; T B : tail bud; L: larva.
For the stages of metamorphosis, see p. 65 (Urbani and De Cesaris Coromaldi, 1954a, b ;
Gaeta, 1957; Urbani, 1957).
dipeptidase in the egg. Changes in activity during embryonic development of Bufo vulgaris are shown in Fig. 3; at the tail bud stage, when
activity is lowest (Urbani, 1957), the highest enzyme content per
unit of reduced weight is found in the cephalic and caudal regions