After experiments carried out on the unicellular green alga
Scenedesmus acutus (Nicolov, 1973 a—c, 1975) it was established that for
the extremely high mutagenic effect of N-nitrosocontaining supermutagens,
except an alkyl radical, is necessary also the presence of a highly polarized
and unbroken
bond in combination with the radical.
Figure 2–81. The structural formula of ethyl-N-nitrososarcosine
A reason for such a conclusion is the absence of mutagenic effect in ethyl-
N-nitrososarcosine. As it is seen from its chemical formula (Fig. 2–81), this
compound differs from N-nitroso N methylurethane and N-nitroso N ethylurethane
(see Table 9) in that the ─ N ─ C ⎯ bond is interrupted by one methylene group (⎯CH₂⎯).
For that reason the mutagenic effect of ethyl-N-nitrososarcosine is 0.02—0.25%, i.e. within
the borders of spontaneous mutations, compared to 38.59% for N-nitroso N-ethylurethane
and 57.10—100% for N-nitroso N-methylurethane (Table 10).
Weak mutagenic effect was manifested by N-nitrosodialkylamines
which doubted their belonging to the group of supermutagens. By
comparing their chemical formulas with those of N-nitrosoalkylurethanes,
N-nitrosoalkylureas and N-nitroso-N′-nitroalkylguanidines (see Table 9) it is
obvious that, though possessing not one but two alkyl radicals, N-
nitrosodialkylamines represent peculiar fragments of the hypothetic
monopeptide units, which are the basic skeleton in the other three groups.
That was the reason to accept that breaking the integrity of
monopeptide ion, which is the basic skeleton in the molecules of N-
nitroso-containing supermutagens, is the cause for the absence of
statistically reliable mutagenic effect of ethyl-N-nitrososarcosine and of the
homologous series of N-nitrosodialkylamine group (Nicolov, 1973 a, b).
Comparing the basic skeleton in the molecules of N-nitroso-containing
supermutagens with the radical, established by Gordy and coauthors
(Gordy, Schields, 1960; Patten, Gordy, 1960) after treating native proteins
with ionizing radiations and determined by EPR-spectroscopy, one is
impressed by the great similarity between their structures (Fig. 2-82). The
obtaining relatively stable radicals after irradiation of proteins having a
structure similar to that of the main skeleton of N-nitroso-containing
supermutagens suggests that it is possible to exist some community of the
mechanisms connected with the initial stages of physical and chemical
mutagenesis, their further action being realized by genetically-active
structures of the cells (Nicolov, 1973 a).