ANTIPEPTIDE ANTIBODIES AGAINST A TORPEDO CYSTEINE-STRING PROTEIN

An antipeptide antiserum was raised against the C-terminal undecapepti de of a Torpedo cysteine-string protein (csp), a putative subunit or m odulator of presynaptic calcium channels. This antiserum was shown to identify selectively the 27-kDa in vitro translation product of the cs p cRNA both by immunoprecipitation and on immunoblots. When affinity-p urified anti-csp antibodies were used to probe immunoblots of membrane proteins from Torpedo electric organ or liver, specific immunoreactiv ity was detected only in electric organ. This immunoreactivity was ass ociated principally with a single protein species of about 34 kDa. The se results indicate that csp immunoreactivity is detectably expressed in electroplax, a heavily innervated tissue, but not in liver, which s hould have an appreciably lower abundance of presynaptic calcium chann el proteins. Moreover, the increased relative molecular mass of csp in electric organ (compared with in vitro translated material) implies t hat csp is posttranslationally modified. Finally, immunoblot analysis of either intact, alkali-treated, or solubilized membrane fractions of electric organ reveals that csp is predominantly a membrane protein.