side chain of three amino acids . The amino acid composition and sequence of the
peptides varies slightly in different species, but this results in considerable changes
in their biological activity. So far eight such polypeptides have been chemically
characterized in the vertebrates ; usually two per species (though one or three ma y
sometimes be present in a single gland). The structures of these hormones are
shown in Fig. 2.4; arginine-vasopressin (ADH) and oxytocin which are present
in mammals, and arginine-vasotocin, which has been identified in species from all
the non-mammalian groups. Vasotocin has the ring sequence of ox ytocin with the
side chain of arginine-vasopressin, and when injected into mammals has some of
the properties of each hormone ; it contracts the uterus, brings about 'milk let down'
Amino acid sequences of the known active natural
neurohypophysial pr inciples':'
A . VASOPRESSOR-ANTIDIURETIC PEPTIDES
1. Arginine vasopressin
I
I
Cys- Tyr-Phe-Gln-Asn-C ys-Pro -Arg-Cly-Nl-l,
1 2
3
4
5
6
7 8 9
2. Lysine vasopressin
I
I
Cys-Tyr-Phe-Gln-Asn-Cys-Pro -Lys-Gly-NH z
3. Arginine vasotocin
I
I
Cys-Tyr- I1e-Gln-Asn-Cys-Pro-Arg-Gl y-NH z
B. NEUTRAL OXYTOCIN-LIKE PEPTIDES
1. Ox yto cin
I
Cys-Tyr- Ile-Cln-Asn-C ys-Pro- Leu-Gl y-NH z
2. Mesotocin (8-isoleucine oxytocin)
j
I
Cys-Tyr-Ile-Gln-Asn-C ys-Pro-Ile-Gly-Nl-I
-
_
z
3. Isotocin (4-serine, 8-isoleucine oxytocin)
t
I
Cys- Tyr-Ile -Ser-Asn-Cys-Pro-I1e-Gl y-NH
- _
_
z
4. Glumitocin (4-serine, 8-glutamine oxytocin)
I
I
Cys- Tyr-I1e-Ser-Asn-C ys-Pro -Gln-Gly-NH z
.:. Amino acids differing from those in the
corresponding positions in the arginine vasopressin
molecule are underlined.
Fig. 2.4 Amino acid sequence of the known active natural neurohypophysial principles
which are distributed in different groups of the vertebrates. (From SAWYER, 1967).
55