INSULIN AND IGF-I RECEPTORS AND TYROSINE KINASE-ACTIVITY IN CARP OVARIES - CHANGES WITH REPRODUCTIVE-CYCLE

Insulin and insulin-like growth factor I (IGF-I) receptors from carp o varies were semipurified with wheat germ agglutinin at different momen ts of the reproductive cycle and their binding characteristics and tyr osine kinase activity were studied. Specific receptors for insulin and IGF-I were found. IGF-I receptors presented higher binding (23.8 +/- 1.5%), number of receptors (965 +/- 20fm/mg) and affinity (K(D) 0.24 /- 0.03nM) than those shown for insulin receptors (4.1 +/- 1%, 530 +/- 85fm/mg and 0.85 +/-0.1nM, respectively). Insulin and IGF-I receptors have a tyrosine kinase activity which is not different from that foun d in muscle of the same species. Seasonal changes were found in bindin g, with maximum values for insulin and IGF-I reached at the end of pre -spawning period (June). However, while IGF-I binding was observed in all stages, insulin binding decreased in autumn and disappeared in win ter, which suggests a different role for the two peptides in ovarian p hysiology.