Taurine binding to the purified insulin receptor

Taurine (2-aminoethanesulfonic acid) was shown to bind specifically and reversibly to the purified human insulin receptor. While insulin binding to the purified insulin receptor exhibited characteristic negative cooperativity and an apparent dissociation constant (Kd) of 1.2 X 10(-9) M, taurine binding was shown to exhibit positive cooperativity and had a lower affinity for the insulin receptor. The apparent Kd for taurine binding to the purified insulin receptor was calculated to be 130 X 10(-9) M and the maximum number of binding sites (Bmax) was 1.6 nmol/mg receptor protein. Chromatographic data demonstrated that taurine binds to the 138,000 molecular weight subunit of the insulin receptor. Taurine binding to the receptor protein was displaced by either taurine or insulin. Anti-human insulin receptor sera prevented insulin or taurine from binding to the receptor. Taurine binding to the protein was pH dependent, and sulfur-containing taurine analogues were able to displace taurine from the insulin receptor. These data supported our previous in vivo and in vitro observations that the hypoglycemic properties of taurine appear to be mediated through an interaction of taurine with the insulin receptor.