122
ALBERTO MONROY AND RACHELE MAGGIO
Although the exact function of the amino-pyrimide-deoxynucleotide
deaminase is not yet clearly understood, it does not seem too far-fetched
to suggest that the dCMP and MedCMP deaminase reactions catalyzed
by Scarano's enzyme, may represent two steps of a cycle of the interconversion of pyrimidine-deoxynucleotides (Scarano and Maggio,
1959b). This cycle would thus involve at least three enzymes : deaminase,
j
ι
Unfertilized Blastula H
Gastrula Ε
Prism
Pluteus
eggs
FIG. 13. Deaminase activity of extracts of eggs and embryos of Sphaerechinus granularis using dCMP (full circles) and MedCMP (empty circles) as substrates. The values on
the ordinate are /XM of substrate deaminated per mg Ν in the extract per 10 minutes.
(From Scarano and Maggio, 1959b.)
reaminase and methylase. These enzymes may regulate the relative concentration of the pyrimidine-deoxynucleotides for optimal DNA synthesis.
In the unfertilized eggs the deaminase is more active than the
enzyme or enzyme systems re-aminating the dUMP (Scarano and
Caserta, unpublished, quoted in Scarano and Maggio, 1959b). This
might bring about an accumulation of dUMP which not only upsets the
deoxynucleotide equilibrium of the pool, but as we know from the
experiments of Nemer, is poorly utilized for the synthesis of thymidylic
acid. This might be one of the factors, if not the factor, responsible for
the blocking of DNA synthesis in the unfertilized egg. At fertilization
the dUMP reaminating system might be activated, thus overcoming the
effect of dCMP deaminase and resulting in the formation of an optimal
amount of dCMP for DNA synthesis.
4h
35
21h
ALBERTO MONROY AND RACHELE MAGGIO
Although the exact function of the amino-pyrimide-deoxynucleotide
deaminase is not yet clearly understood, it does not seem too far-fetched
to suggest that the dCMP and MedCMP deaminase reactions catalyzed
by Scarano's enzyme, may represent two steps of a cycle of the interconversion of pyrimidine-deoxynucleotides (Scarano and Maggio,
1959b). This cycle would thus involve at least three enzymes : deaminase,
j
ι
Unfertilized Blastula H
Gastrula Ε
Prism
Pluteus
eggs
FIG. 13. Deaminase activity of extracts of eggs and embryos of Sphaerechinus granularis using dCMP (full circles) and MedCMP (empty circles) as substrates. The values on
the ordinate are /XM of substrate deaminated per mg Ν in the extract per 10 minutes.
(From Scarano and Maggio, 1959b.)
reaminase and methylase. These enzymes may regulate the relative concentration of the pyrimidine-deoxynucleotides for optimal DNA synthesis.
In the unfertilized eggs the deaminase is more active than the
enzyme or enzyme systems re-aminating the dUMP (Scarano and
Caserta, unpublished, quoted in Scarano and Maggio, 1959b). This
might bring about an accumulation of dUMP which not only upsets the
deoxynucleotide equilibrium of the pool, but as we know from the
experiments of Nemer, is poorly utilized for the synthesis of thymidylic
acid. This might be one of the factors, if not the factor, responsible for
the blocking of DNA synthesis in the unfertilized egg. At fertilization
the dUMP reaminating system might be activated, thus overcoming the
effect of dCMP deaminase and resulting in the formation of an optimal
amount of dCMP for DNA synthesis.
4h
35
21h