ADENYLATE-CYCLASE - THE MORE MEMBRANE-ASSOCIATED, THE LESS RADIOSENSITIVE

A dose dependent but not parallel decreases were observed both in SH c ontent and catalytic activity of ''free'' catalytic subunit after irra diation (0-3200 Gy), while SH groups of membrane-associated adenylate cyclase were insensitive (under 3200 Gy). An initial ''radioactivation '' of membrane-associated enzyme was found under 800 Gy, then an inhib ition above 1600 Gy. The SH alkylating agent, N-ethylmaleimide resulte d in a complete inactivation, both of membrane associated form of aden ylate cyclase and ''free'' catalytic subunit with similar inactivation profiles. These data indicate that in the radiosensitivity or ''radio protection'' of adenylate cyclase, its membrane association/integratio n might play a more important role than the SH groups themselves.