The effect of metals on the S-S polypeptide receptor in depolarized rat uterus

1. Metals potentiate the contractile effects of S-S polypeptides in depolarized rat uterus. Their order of potency is Co(++)>/=Co(+++)>/=Mn(++)>/=Ni(++)>/= Mn(+++)>Zn(++)>/=Mg(++)>Fe(++)>Fe(+++)>/= Ca(++)>Be(++)=Sr(++)=Ba(++)=Cu(++)=O.2. S-S polypeptides with relatively weak oxytocic activity such as lys-vasopressin, arg-vasopressin and orn-vasopressin are strongly potentiated by metals while highly active polypeptides such as oxytocin are weakly potentiated.3. Potentiation by metals was specific for S-S polypeptides; other polypeptides (bradykinin, hypertensin) as well as acetylcholine and isoprenaline were unaffected.4. Potentiation by metals occurs rapidly and is fully reversible. In all cases some activity was retained by S-S polypeptides even in the complete absence of metals.5. A scheme which could account for the observed effects has been formulated. This assumes the formation of a ternary complex between receptor, metal and polypeptide leading to improved alignment between polypeptide and receptor.6. Analogies are discussed between metal enzymes and the S-S polypeptide receptor for which the term metal receptor is proposed.