Marked ion dependence of 125I-angiotensin I binding to atypical sites on Mycoplasma hyorhinis

125I-Ang I binding to atypical sites on Mycoplasma hyorhinis-contaminated IEC-18 cell membranes increased with increasing pH and [NaCl] (ED50 at 500 mM; maximal 13-fold increase at 2 M NaCl). Alkali metal chlorides and sodium halides increased binding with rank orders of Na+ < K+ < Rb+ < Cs+ = Li+ and F- < Cl- < Br < I. Covalent cross-linking of 125I-Ang I labeled a discrete band of 97 kDa. These findings suggest that the site is not a G protein-coupled receptor, but may play a role in the sensing by Mycoplasma of the ionic composition and/or pH of its environment.