82
ENRICO URBANI
this would explain the very low enzymatic activity observed shortly
before the larval stage, as a result of the reduced availability of carbohydrate substrates at this stage.
Changes in amylase activity during metamorphosis follow a similar
pattern to that of the embryonic stage: the high initial activity markedly
decreases up to stage IV of metamorphosis. As during embryonic development, this coincides with a high degree of carbohydrate utilization.
D. Lipases
The enzymes known as lipases are rather difficult to classify: the term
generally includes esterases responsible for the hydrolysis of esters
formed from glycerol and natural fatty acids with long carbon atoms
chains. For this reason, a clear-cut distinction between lipases and other
esterases is hardly possible, and we refer our reader to the work of
Sumner and Somers (1953) for a clear and exhaustive treatment of these
problems.
To avoid misunderstandings, for the purposes of this survey, lipase is
regarded as that enzyme or those enzymes which hydrolyse, at approximately p H 9, tributyrin into its two constituents, glycerol and butyric
acid.
Lipases show negligible activity in the egg of Rana esculenta) the
values obtained for the initial stages of development can be considered
as being within the limits of experimental error of the titrimetric procedure used. More appreciable activity is shown at the tail bud stage
and as the embryo develops there is a steady increase in enzymatic
activity, which persists for a short period in the non-feeding larva, and
then activity falls rapidly (Fig. 11).
The shape of the curve closely resembles that of acid proteinase
activity, the only difference being that lipase activity does not decrease
until yolk resorption is complete, whereas proteinase activity falls
rapidly at the end of the embryonic stage (Urbani and Scollo Lavizzari,
1955b; Urbani, 1957). Our co-worker Russo-Caia (1956) studied lipase
activity in Bufo vulgaris, and unexpectedly obtained a different activity
curve from that for Rana esculenta. In the case of B. vulgaris activity
increased from the blastular to tail bud stage, then decreased rapidly
for a short period, and subsequently increased again steadily, reaching
a maximum in the non-feeding larva. Lipase activity in Rana dalmatina
and Bufo viridis followed the same pattern as in R. esculenta (Urbani
et al., 1957). In other words, among the species so far considered, only
Bufo vulgaris shows a peculiar pattern of activity (Fig. 12). These
findings are interesting not only with respect of the activity of these
enzymes during embryonic development, but also to their different
behaviour in various species.
ENRICO URBANI
this would explain the very low enzymatic activity observed shortly
before the larval stage, as a result of the reduced availability of carbohydrate substrates at this stage.
Changes in amylase activity during metamorphosis follow a similar
pattern to that of the embryonic stage: the high initial activity markedly
decreases up to stage IV of metamorphosis. As during embryonic development, this coincides with a high degree of carbohydrate utilization.
D. Lipases
The enzymes known as lipases are rather difficult to classify: the term
generally includes esterases responsible for the hydrolysis of esters
formed from glycerol and natural fatty acids with long carbon atoms
chains. For this reason, a clear-cut distinction between lipases and other
esterases is hardly possible, and we refer our reader to the work of
Sumner and Somers (1953) for a clear and exhaustive treatment of these
problems.
To avoid misunderstandings, for the purposes of this survey, lipase is
regarded as that enzyme or those enzymes which hydrolyse, at approximately p H 9, tributyrin into its two constituents, glycerol and butyric
acid.
Lipases show negligible activity in the egg of Rana esculenta) the
values obtained for the initial stages of development can be considered
as being within the limits of experimental error of the titrimetric procedure used. More appreciable activity is shown at the tail bud stage
and as the embryo develops there is a steady increase in enzymatic
activity, which persists for a short period in the non-feeding larva, and
then activity falls rapidly (Fig. 11).
The shape of the curve closely resembles that of acid proteinase
activity, the only difference being that lipase activity does not decrease
until yolk resorption is complete, whereas proteinase activity falls
rapidly at the end of the embryonic stage (Urbani and Scollo Lavizzari,
1955b; Urbani, 1957). Our co-worker Russo-Caia (1956) studied lipase
activity in Bufo vulgaris, and unexpectedly obtained a different activity
curve from that for Rana esculenta. In the case of B. vulgaris activity
increased from the blastular to tail bud stage, then decreased rapidly
for a short period, and subsequently increased again steadily, reaching
a maximum in the non-feeding larva. Lipase activity in Rana dalmatina
and Bufo viridis followed the same pattern as in R. esculenta (Urbani
et al., 1957). In other words, among the species so far considered, only
Bufo vulgaris shows a peculiar pattern of activity (Fig. 12). These
findings are interesting not only with respect of the activity of these
enzymes during embryonic development, but also to their different
behaviour in various species.