ISOLATION AND PARTIAL CHARACTERIZATION OF THE INSULIN BINDING-SITES OF TETRAHYMENA-PYRIFORMIS

The free-living protozoan, Tetrahymena pyriformis, has been shown to s pecifically bind insulin. Insulin causes alterations in metabolic func tion and an increase in insulin binding capacity (hormonal imprinting) in this organism. Previously, an insulin-like material was found in b oth Tetrahymena cell isolates and in their growth media. The purpose o f this study was to isolate and partially characterize the ciliary mem brane binding sites for insulin. The methods employed, DEAE and affini ty chromatography, were published previously for the mammalian insulin receptor. Here we report, not the isolation of a mammalian-like recep tor protein, but a ciliary membrane protein (62-67 kDa) that is immuno logically similar to insulin. This insulin-like protein may function a s both precursor to a soluble form and membrane-bound binding site/rec eptor as has been suggested for Euplotes pheromones and mammalian grow th factors such as transforming growth factor a and epidermal growth f actor. (C) 1995 Academic Press, Inc.