Comparative study of binding of Scorpaena porcus scorpion fish insulin and pig insulin by specific muscle plasma membrane receptors

Insulin from the scorpion-fish and porcine insulin have been compared with respect to their capacity to interact with the specific receptors in plasma membrane of skeletal muscle fibers of rats. Both insulins inhibited membrane binding of insulin-125J; the dose of porcine insulin which inhibited binding by 50% was equal to 3.7 nM, that of fish insulin -- to 100 nM. These figures indicated lower affinity of fish insulin to mammalian receptors (4% of the porcine affinity), being in accordance with lower biological activity of fish insulin in diaphragmal test. Other peculiarity of fish insulin was revealed in studies on dissociation of insulin-125J, which was previously bound to isolated diaphragm muscle of the rat. In contrast to mammalian insulin, it was not capable of increasing the dissociation when being added to a solution in doses from 7.10(-11) to 7.10(-9) M. This fact is analysed in term of the "site--site" interactions concept.