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

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Abstract
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.