Acetylcholine receptors from Torpedo and Electrophorus have similar subunit structures

Previously, acetylcholine receptor purified from the electric organs of electric eels (Electrophorus electricus) and electric rays (Torpedo californica) (torpedo) had appeared to differ in subunit structure. Receptor from torpedo has the subunit structure alpha 2 beta gamma delta, but subunits corresponding only to alpha, beta, and gamma had been observed in receptor from eel. Here we report that if membrane fragments of eel electric organ are prepared and detergent extracted in the presence of iodoacetamide, then receptor purified from the extract contains a fourth subunit. Using monoclonal antibodies as well as conventional antisera, we show that the newly recognized subunit of receptor from eel corresponds to the delta subunit of torpedo. A monoclonal antibody to the delta subunit of torpedo cross-reacts with the gamma subunit and shows a similar cross-reaction between the delta' and gamma' subunits of receptor from eel, indicating the presence of an unexpected structural similarity. Although the function of the beta, gamma, and delta subunits remains unknown, these results support the concept that receptors from the electric organs of several species and probably also from muscle share a similarly complex subunit structure.