136
A. M. PERKS
its oxytocic effect was potentiated twofold by the addition of magnesium
ions. The presence of a peak of similar mobility-although not necessarily
of the same chemical constitution-has been confirmed by a number of
other workers, and extended to include Squalus acanthim (Pacific variety
= Squalus suckleyi), Dasyatis sabina, Carcharinus leucm, Sphyrna mokurran, and Eulania milberti (Perks, 1966; W. H. Sawyer, 1967; Swiatkiewicz et ul., 1967). Perks (1966) has shown that the behavior of this
component is parallel to that of oxytocin in a large number of chromatography systems, and it would appear to be an oxytocinlike, neutral
principle, or principles. However, it is not the same as oxytocin, since it is
potentiated by magnesium ions, and it possesses other biological differences from the mammalian principle (Squalus acanthim, W. H. Sawyer:
1965b; Swiatkiewicz et al., 1967). In Squalus acanthias, this major component can be purified by column chromatography, and it appears to have
a relatively high potency (70 U/mg, W. H. Sawyer, 1967; 110 U/mg,
Heinicke and Perks, 1969a). Column partition chromatography of the
purified product, on a system which would separate oxytocin, 8 Ile oxytocin, and 4 Ser, 8 Ile oxytocin suggests that it is a homogenous peptidebut this has not yet been confirmed by amino acid analysis (Squulus acanthias, W. H. Sawyer, 1967).
The second oxytocic peak resolved by Heller and his group was
a slow-running component, which moved with the Rf of a basic
principle, similar to arginine vasotocin or the mammalian vasopressins.
It was designated ‘‘El.’’ It showed a distinctive spectrum of biological
activities, which included a remarkable sixfold potentiation of its oxytocic potency by the presence of magnesium ions. However, in Negaprion brevirostris the potentiation was closer to the twofold value
of the fast-running E, peak. This suggested that the properties of the
slow-running component could vary in different species. Moreover, there
was reason to suppose that it did not exist in all extracts. Acher and his
co-workers did not observe a peptide which combined the properties of
the El principle during their purification and analysis of skate extracts
(see below). Other groups, using the same paper chromatography methods as those of Heller and his co-workers, failed to detect a principle
with the properties of the El peptide. Perks (1966) and Swiatkiewicz
et al. (1967), working with Squalus acanthias and other species, could
only resolve a single fast-moving oxytocic peak with a uniform twofold
magnesium potentiation throughout its length. At first, overloading artifacts were avoided by the use of relatively low doses of crude extracts,
but later, extracts were subjected to gentle preliminary purification by gel
filtration on Sephadex columns, and it was found possible to chromatograph quantities as high as 7000 mU of oxytocic activity. Even at such
A. M. PERKS
its oxytocic effect was potentiated twofold by the addition of magnesium
ions. The presence of a peak of similar mobility-although not necessarily
of the same chemical constitution-has been confirmed by a number of
other workers, and extended to include Squalus acanthim (Pacific variety
= Squalus suckleyi), Dasyatis sabina, Carcharinus leucm, Sphyrna mokurran, and Eulania milberti (Perks, 1966; W. H. Sawyer, 1967; Swiatkiewicz et ul., 1967). Perks (1966) has shown that the behavior of this
component is parallel to that of oxytocin in a large number of chromatography systems, and it would appear to be an oxytocinlike, neutral
principle, or principles. However, it is not the same as oxytocin, since it is
potentiated by magnesium ions, and it possesses other biological differences from the mammalian principle (Squalus acanthim, W. H. Sawyer:
1965b; Swiatkiewicz et al., 1967). In Squalus acanthias, this major component can be purified by column chromatography, and it appears to have
a relatively high potency (70 U/mg, W. H. Sawyer, 1967; 110 U/mg,
Heinicke and Perks, 1969a). Column partition chromatography of the
purified product, on a system which would separate oxytocin, 8 Ile oxytocin, and 4 Ser, 8 Ile oxytocin suggests that it is a homogenous peptidebut this has not yet been confirmed by amino acid analysis (Squulus acanthias, W. H. Sawyer, 1967).
The second oxytocic peak resolved by Heller and his group was
a slow-running component, which moved with the Rf of a basic
principle, similar to arginine vasotocin or the mammalian vasopressins.
It was designated ‘‘El.’’ It showed a distinctive spectrum of biological
activities, which included a remarkable sixfold potentiation of its oxytocic potency by the presence of magnesium ions. However, in Negaprion brevirostris the potentiation was closer to the twofold value
of the fast-running E, peak. This suggested that the properties of the
slow-running component could vary in different species. Moreover, there
was reason to suppose that it did not exist in all extracts. Acher and his
co-workers did not observe a peptide which combined the properties of
the El principle during their purification and analysis of skate extracts
(see below). Other groups, using the same paper chromatography methods as those of Heller and his co-workers, failed to detect a principle
with the properties of the El peptide. Perks (1966) and Swiatkiewicz
et al. (1967), working with Squalus acanthias and other species, could
only resolve a single fast-moving oxytocic peak with a uniform twofold
magnesium potentiation throughout its length. At first, overloading artifacts were avoided by the use of relatively low doses of crude extracts,
but later, extracts were subjected to gentle preliminary purification by gel
filtration on Sephadex columns, and it was found possible to chromatograph quantities as high as 7000 mU of oxytocic activity. Even at such