Adenylate Cyclase-the More Membrane Associated, the Less Radiosensitive.

Abstract

A dose dependent but not parallel decreases were observed both in SH content and catalytic activity of "free" catalytic subunit after irradiation (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 inhibition above 1600 Gy. The SH alkylating agent, N-ethylmaleimide resulted in a complete inactivation, both of membrane associated form of adenylate cyclase and "free" catalytic subunit with similar inactivation profiles. These data indicate that in the radiosensitivity or "radioprotection" of adenylate cyclase, its membrane association/integration might play a more important role than the SH groups themselves.

Distribution of Adenylyl Cyclase and Guanylyl Cyclase in Rat Tissues

“…It contained 0.1 mM adenine to decrease the specific radioactivity of nonphosphorylated of ATP generated during the reaction, 4 mM MgSO 4 , 2 mM cAMP, 0.1 mM GTP, 45 mM Tris-HCl buffer (pH 7.4) containing 10 mM theophylline and 6 mM 2-mercaptoethanol, 0.5 mM (1.0 µCi) [2-3 H] ATP. Finally, 2 µl ethanol were added to increase the membrane fluidity of the homogenate [12] . All components were mixed gently and the tubes were incubated at 37ºC for 10 min and the reaction was stopped with 20 µl of 2.2 M HCl.…”